Please recommend a charge controller for this system...

RegGuheert · January 2011

I am specifying an off-grid PV system for a new house that my sister is building. Here are some system details for parts which are already bought:

PV: 20-Sharp NU-U240F1 60-cell panels (Total 4800 Wp)
Batteries: 4-Rolls Surrette 12 CS 11P Batteries (12V, 357AH @ 20hr)
Inverter: Xantrex XW6048

I had been considering purchasing the new Xantrex XW MPPT 80 600 charge controller, but the recent recall on their GT inverters gives me pause. Also, the equipment has now moved from being ~150 feet away from the array to directly underneath the array. Therefore we now have many more options.

Under current consideration are the following, but I am open to ANY available MPPT charge controllers:

2-Xantrex XW MPPT 60 150
Xantrex XW MPPT 80 600
Outback Flexmax 80
Midnite Classic200

I really want to purchase a charge controller that will be very efficient and very reliable. As such, I'm not convinced the HV Xantrex unit is up to the task. We will be installing the XW system controller, so XW equipment is attractive, but not if they are unreliable.

The problem with the LV Xantrex and the Outback is the 150V limit, which effectively means we would have to wire the array in strings of three, which really doesn't work for this system. I'm leaning towards the Midnite Solar Classic 200 since I could go with strings with four panels each. (Plus you GOTTA LOVE that art deco case! 8))

So please tell me which controllers you like or dislike for this application and the reasons why. Please don't limit your response to the above list if there are others I should be considering. If you have any horror stories with any of these units, please let me hear them. Thanks in advance!

Edit: Actually, it looks like I can use the Midnite Classic 150. Does anyone think I will get into trouble with maximum voltage using that charge controller?

Cariboocoot · January 2011

Re: Please recommend a charge controller for this system...

Let's see if I'm reading this right:

It has a 375 Amp hour, 48 Volt battery bank?

That's roughly 37.5 Amps peak current @ 57 Volts charging = 2137 Watts, or about 2800 without the derating.

What's the other 2000 Watts of panel for?

A 4800 Watt array would give numbers like this:

4800 @ 77% = 3696/57 Volts = approximately 65 Amps peak current. Enough for double that size battery bank (750 Amp hours @ 8.5% charge rate).

The 375 Amp hour bank could give you about 9 kW hours maximum to work with.

If the first numbers are right, then you could use any MPPT controller over 40 Amps, including the Morningstar 45 Amp: http://www.solar-electric.com/motr45ampmps.html

If you need the full panel output you need to be able to handle 65+ Amps, and that means either multiple controllers or the Outback FM80.

Or maybe I've read it all wrong. Just wondering how you picked the equipment you have so far.

RegGuheert · January 2011

Re: Please recommend a charge controller for this system...

Are you saying that I cannot charge this battery faster than C/10? What is the problem with charging faster than that? Does the voltage get too high?

The system is designed to have most of the loads occur during the daytime, so the battery capacity needed at nighttime should be quite low, perhaps ~4 kWh or about 21% DOD. Daytime consumption may be quite a bit higher. Insolation in December and January should *average* 3 full-sun-hours with the 50 degree array tilt being used, giving ~11 kWh on an average day, which should be enough to keep the generator off for most days except those stretches when there is little to no sun. Time will tell.

Cariboocoot · January 2011

Re: Please recommend a charge controller for this system...

As a rule, the upper charge limit is 13% of the 20hr Amp hour capacity. For 375 Amp hours that would be 48.75 Amps. Unless the battery manufacturer specifically says they can take a higher rate. 65 Amps would be 17%, and would lead to excessive heating resulting in plate damage and premature battery death.

With your expected Winter insolation and intended load shifting (smart move) I can see why you want more panels. But to make use of them you'll have to limit the charge rate to prevent battery damage. As you know, net charge rate is what counts. An additional "30 Amps" capacity is like having 1400 Watts that needs to go somewhere. Over 3 hours sun time that's an additional 4 kW hours.

Personally, I'd increase the battery bank size and have the additional power available whenever needed, including an extra margin for cloudy days.

RegGuheert · January 2011

Re: Please recommend a charge controller for this system...

Thanks, Marc!

I will certainly take a closer look at this! Yeah, part of it is specification creep. Batteries started out at 25 kWh and array at 4 kW, but now we are where we are. Let me look more closely at what Surrette says and I may make some adjustments to the battery.

Thanks again!

BTW, if we go with the Midnite Solar Classic 150 charge controller, that can go up to 73 amps. In that case, we can get away with only one charge controller. Any one have an opinion on that unit, good or bad? Where can I find efficiency numbers for it?

BB. · January 2011

Re: Please recommend a charge controller for this system...

Typical lead acid storage batteries have a recommended limit around C/8 or 13% rate of charge (20 hour rate). If you want to charge faster than that, the battery may need physical cooling.

You can connect upwards of 20-30% worth of charging sources--But for the most part, once the battery reaches ~14.5 volts charging--the chargers will start dialing back on the current.

By the way, if you do charge >C/8 rates--You should use chargers that have remote battery temperature sensors. What happens is as the batteries get hot, their intrinsic voltage (charging/resting) voltage falls... It is possible for a "high performance charger" to overheat the battery, it sees charging voltage fall, and continues to pump current (or even increase current) because it mistakes the falling voltage for an undercharged battery and/or other DC loads being brought on-line. This is called "thermal runaway". How often it happens and how much of a risk it is--I am not the guy to guess at that (others know more than I).

Most "good quality" chargers have an internal temperature sensor--but that only measures the temperature of the charge controller--not of the battery bank.

With solar panels--going for over 13% rate of charge gets expensive to hav e all of those panel that you may not be able to fully use.

If you have heavy loads during the day (pumping, etc.) that you can power with the extra solar panels--go for it.

What we ask people, besides conservation, is what is solar power worth to them and how much they use summer and winter... For many people, designing the system to operate 9 months of the year without generator use, and then filling in stretches of cloudy winter with generator use, tends to be a good trade off...

Saves having to oversize the battery bank for more than 3 days of no sun and recognizes that for areas with dark and stormy weather, a system may produce only 10% or 5% or even less of rated power--So it is almost impossible to have enough solar panels to ride through a week or two of bad weather without having the generator backup anyway.

As a rough rule of thumb, in the US, solar power costs on the order of $1-$2+ per kWH (assuming 20 year life, replacement of battery bank every X years, replacement of electronics every Y years, and no cost of money), or about 10x as expensive as utility or even Grid Tied solar power.

We are not trying to make the decision for you--just give you the information so that you can make the best decisions for your needs.

-Bill

Cariboocoot · January 2011

Re: Please recommend a charge controller for this system...

Have you seen this thread on the Midnight Classic? http://forum.solar-electric.com/showthread.php?t=8808

Seems the production units are just now making their way to end users. Tallgirl has one, but too early to get any field evaluations yet! If I recall correctly, they continually adjust charge rate for optimum performance, like the Rogue (as opposed to the sporadic sampling sweeps done by most controllers).

RegGuheert · January 2011

Re: Please recommend a charge controller for this system...

Update: My sister called her battery vendor and asked about the possibility of changing the order from four 357AH 12V batteries to six 546AH 8V batteries. No issue with availability, as they will be arriving on the same truck. HOWEVER, six 8V batteries will cost 2.25X what four 12V batteries cost!

Anyway, we've decided to stick with the batteries she has coming.

Cariboocoot wrote: »

Have you seen this thread on the Midnight Classic? http://forum.solar-electric.com/showthread.php?t=8808

Seems the production units are just now making their way to end users. Tallgirl has one, but too early to get any field evaluations yet! If I recall correctly, they continually adjust charge rate for optimum performance, like the Rogue (as opposed to the sporadic sampling sweeps done by most controllers).

Thanks for this link! I have read it through and I've decided to go for the Classic 200 controller. It has what I'm looking for! Hopefully my sister can purchase one in the next couple of months...

It limits at 70A, so it should be able to take all the power from the array, except on the coldest days (like today), assuming the battery can handle it. Otherwise, it will limit the current. After all that IS one of the main functions of a charge controller, is it not? :roll:

In wintertime is when I really need the extra PV/batteries/everything, but since the installation is outside, the batteries will be cold whenever the PV is cold, so that works out. No way will we EVER see 4kW from this array in the summer. It will be too hot and the sun will never go through the boresight of the array. Daily loads may be rather high in summer due to the use of ceiling fans, though. Spring and fall the battery will likely be fully charged always anyway, so I figure it will be limiting regardless of what we do.

BB. wrote: »

Typical lead acid storage batteries have a recommended limit around C/8 or 13% rate of charge (20 hour rate). If you want to charge faster than that, the battery may need physical cooling.

Agreed, but perhaps not in wintertime when I think this will matter. We'll see.

BB. wrote: »

You can connect upwards of 20-30% worth of charging sources--But for the most part, once the battery reaches ~14.5 volts charging--the chargers will start dialing back on the current.

Agreed. If the battery is full enough not to take all of what the array can produce, then that's probably a good thing!

BB. wrote: »

You By the way, if you do charge >C/8 rates--You should use chargers that have remote battery temperature sensors. What happens is as the batteries get hot, their intrinsic voltage (charging/resting) voltage falls... It is possible for a "high performance charger" to overheat the battery, it sees charging voltage fall, and continues to pump current (or even increase current) because it mistakes the falling voltage for an undercharged battery and/or other DC loads being brought on-line. This is called "thermal runaway". How often it happens and how much of a risk it is--I am not the guy to guess at that (others know more than I).

Most "good quality" chargers have an internal temperature sensor--but that only measures the temperature of the charge controller--not of the battery bank.

Agreed on the need for a temperature sensor in this setup. That is one reason I have decided to go with the MidNite Solar Classic 200. Thanks for the recommendation!

BB. wrote: »

With solar panels--going for over 13% rate of charge gets expensive to hav e all of those panel that you may not be able to fully use.

If you have heavy loads during the day (pumping, etc.) that you can power with the extra solar panels--go for it.

What we ask people, besides conservation, is what is solar power worth to them and how much they use summer and winter... For many people, designing the system to operate 9 months of the year without generator use, and then filling in stretches of cloudy winter with generator use, tends to be a good trade off...

Saves having to oversize the battery bank for more than 3 days of no sun and recognizes that for areas with dark and stormy weather, a system may produce only 10% or 5% or even less of rated power--So it is almost impossible to have enough solar panels to ride through a week or two of bad weather without having the generator backup anyway.

As a rough rule of thumb, in the US, solar power costs on the order of $1-$2+ per kWH (assuming 20 year life, replacement of battery bank every X years, replacement of electronics every Y years, and no cost of money), or about 10x as expensive as utility or even Grid Tied solar power.

We are not trying to make the decision for you--just give you the information so that you can make the best decisions for your needs.

-Bill

Panels are already installed, actually, so that cost is done. The price was about $2.90/Wp installed, so not too bad. I don't understand why the batteries are geometrically more expensive per AH, but they appear to be in this case. Hopefully the charge controller will do what it needs to do to protect the batteries and get a good lifetime out of them.

We will have a propane-powered generator for backup, but that is not yet purchased. Look for another thread on that!

Who knows, perhaps we will use a diversion controller like the one Midnight offers to perform other functions when there is extra PV around. We'll see!

Thanks for all the help with this! Other thoughts?

Cariboocoot · January 2011

Re: Please recommend a charge controller for this system...

I'm not surprised the 8V batteries are more: less demand = lower production = higher cost per unit. In terms of $/Amp hour, the basic "golf cart" batteries turn out to be the best bargain because they're the ones that sell the most. But not always suitable for the application.

The thing about cold weather isn't the Amps, it's the Volts. Specifically the Voc which can run above the charge controller's input limits when the panels super conduct in very cold weather. I think the Midnight has a 150 Volt limit, which is pretty good. I had a "nominal" 72 Volt array shut down my MX60, which has the same input limit. Even though the Voc should have been approx 135 Volts, at the seriously minus numbers we achieve here in the Cariboo it went above that!

RegGuheert · January 2011

Re: Please recommend a charge controller for this system...

Cariboocoot wrote: »

The thing about cold weather isn't the Amps, it's the Volts. Specifically the Voc which can run above the charge controller's input limits when the panels super conduct in very cold weather. I think the Midnight has a 150 Volt limit, which is pretty good. I had a "nominal" 72 Volt array shut down my MX60, which has the same input limit. Even though the Voc should have been approx 135 Volts, at the seriously minus numbers we achieve here in the Cariboo it went above that!

Yeah, that's why I don't want to go with the Outback. The VOC for Midnight is supposed to be batteryV PLUS rating. So for the Classic 200 we are purchasing, I should be able to go up to 250V or so. I plan on using four panels in series, so nominal VOC will be 150. Hopefully that won't break it. If it does, I'll tell the manufacturer their specs are incorrect and request they swap me up to the Classic 250. We'll see how that goes.

niel · January 2011

Re: Please recommend a charge controller for this system...

coot,
they indicated a classic 200 which has a higher input voltage than the 150. there is another one with even higher voltage capability and is the 250 and one that even charges a 120vdc battery bank too.8)

regguheert,
the max current limit wasn't designed with the expressed purpose of holding back on the bulk current as many designers of controllers i'm sure would've loved that to be open ended. they had to add components to allow more max current to flow and as such they didn't have in mind to limit you, but component numbers and complexities adding to costs is more of the limiting factors on more current. with outputs as they are, one just needs to add another controller in parallel if the max limit is exceeded. the only time they really wanted to limit things is when it comes to absorb and float charges and as such the bulk current limit is not a feature because it limits, but just happens to be its max capability.

stephendv · January 2011

Re: Please recommend a charge controller for this system...

Regarding the Classic's voltage limits, the "hypervoc" function of adding battery voltage to the Voc rating is purely a safety feature - the controller will stop charging once the Voc passes the input limit. E.g. with a 150 controller, it will shut down above 150V, but with a 48V battery it won't burn out till 200V.

http://midnitesolar.com/smf_forum/index.php?topic=41.msg211#msg211

RegGuheert · January 2011

Re: Please recommend a charge controller for this system...

niel wrote: »

regguheert,
the max current limit wasn't designed with the expressed purpose of holding back on the bulk current as many designers of controllers i'm sure would've loved that to be open ended. they had to add components to allow more max current to flow and as such they didn't have in mind to limit you, but component numbers and complexities adding to costs is more of the limiting factors on more current. with outputs as they are, one just needs to add another controller in parallel if the max limit is exceeded. the only time they really wanted to limit things is when it comes to absorb and float charges and as such the bulk current limit is not a feature because it limits, but just happens to be its max capability.

Understood, and that is what I want. I have chosen this charge controller to try to ensure I can take advantage of the full charging current available from the array if it can be accepted by the batteries for the given SOC and charging condition. My reading of the Rolls Surrette technical bulletins tells me that as long as I keep the bulk charge voltage between 2.37 and 2.45 volts per cell (temperature compensated, I assume) the battery is designed to handle the current. I expect to *rarely* have currents above the C/8 rule-of-thumb available from the array, and then only for an hour or two at a time. IMO, if the state-of-charge of the battery is low then I want to take advantage of the array to return the charge quickly. All that said, we need to see how things go, since the load estimates are just that and could be somewhat different from expectations. We will need to observe operations through the first year and make adjustments as needed. The logging and monitoring features of the Classic controllers are an attractive feature in this regard.

stephendv wrote: »

Regarding the Classic's voltage limits, the "hypervoc" function of adding battery voltage to the Voc rating is purely a safety feature - the controller will stop charging once the Voc passes the input limit. E.g. with a 150 controller, it will shut down above 150V, but with a 48V battery it won't burn out till 200V.

http://midnitesolar.com/smf_forum/index.php?topic=41.msg211#msg211

Thanks, Stephen! This confirms that I need to go with at least the Classic 200, since I want to operate the array in strings of four panels in cold weather. The temperature around here rarely gets below 0F, but in my lifetime it may have gotten down to -20F or about -25C, which is 50C below where (I think) the Sharp NU-U240F1 is rated. VOC for one panel is given as 37.4V and the temperature coefficient is given as -0.351%/C, so here is what I come up with:

Worst-case VOC = 4 * ((1 + (50 * 0.00351)) * 37.4V) = 175.8V

That should give me about 25V worst-case headroom for operation and about 75V worst-case headroom for damage. Does that calculation look right to everyone? Does anyone think I need to move to the Classic 250?

BTW, it is annoying that MidNite solar requires registration to simply read their forum. Nowhere in their manual do they define the term "Hyper VOC", though they use it in the specification table. Since it appears that this is a term that MidNite solar has invented, it seems contingent upon them to define what it means somewhere. IMO, since these products are now shipping ALL necessary application information should be made publicly available.

RegGuheert · January 2011

Re: Please recommend a charge controller for this system...

stephendv wrote: »

Regarding the Classic's voltage limits, the "hypervoc" function of adding battery voltage to the Voc rating is purely a safety feature - the controller will stop charging once the Voc passes the input limit. E.g. with a 150 controller, it will shut down above 150V, but with a 48V battery it won't burn out till 200V.

http://midnitesolar.com/smf_forum/index.php?topic=41.msg211#msg211

Looking at this further, if that is REALLY how it works, then I think they need to change their manual. The specification in the manual is "Operating Volts in" and the values are 150, 200 or 250 depending on the unit. Since this is an MPPT controller, "Operating Volts in" implies the MPPT voltage, not VOC.

Cariboocoot · January 2011

Re: Please recommend a charge controller for this system...

RegGuheert wrote: »

Looking at this further, if that is REALLY how it works, then I think they need to change their manual. The specification in the manual is "Operating Volts in" and the values are 150, 200 or 250 depending on the unit. Since this is an MPPT controller, "Operating Volts in" implies the MPPT voltage, not VOC.

Actually you mean Vmp, not Voc. It is a bit confusing.

I would have written it as "Maximum Input Voltage = 150/200/250 + nominal system Voltage. Voc of panels should not exceed this level."

RegGuheert · January 2011

Re: Please recommend a charge controller for this system...

Cariboocoot wrote: »

Actually you mean Vmp, not Voc. It is a bit confusing.

I would have written it as "Maximum Input Voltage = 150/200/250 + nominal system Voltage. Voc of panels should not exceed this level."

Agreed Vmp is the standard way to say this for PV. I'm wondering if they are using other terminology for these controllers since they also work for windo and hydro. Dunno.

Until they provide more details, I will interpret the following terms in the manual this way:

"Operating Volts in" = Maximum Vmp at which this controller will operate. Vmp above this point will result in shutdown of the unit.

"Max Hyper VOC" = Absolute maximum VOC above which permanent damage to the unit may occur.

Cariboocoot · January 2011

Re: Please recommend a charge controller for this system...

Terminology can drive you nuts, can't it? In any conversation it always helps if at least one of the people actually is expressing himself correctly!

In terms of PV & controller, maximum Volts in should be the limit for Voc, as Vmp is always lower. It's throwing that word "operating" in that skews the meaning. Maybe their intent is that the maximum operating Voltage (150/200/250) is Vmp, and the "hyper" part (addition of the nominal system Voltage) gives the necessary "cushion" for Voc?

Mostly I think I've just explained why I'm confused about it.

RegGuheert · January 2011

Re: Please recommend a charge controller for this system...

Cariboocoot wrote: »

In terms of PV & controller, maximum Volts in should be the limit for Voc, as Vmp is always lower.

I disagree. Maximum applies to many other things besides damage limits.

Cariboocoot wrote: »

It's throwing that word "operating" in that skews the meaning. Maybe their intent is that the maximum operating Voltage (150/200/250) is Vmp, and the "hyper" part (addition of the nominal system Voltage) gives the necessary "cushion" for Voc?

That's my interpretation, but "Operating Volts in" says NOTHING to me. It MUST be a maximum. Otherwise, they are trying to say that is the ONLY operating voltage for the unit, which is highly unlikely.

Cariboocoot wrote: »

Mostly I think I've just explained why I'm confused about it.

Me, too!

RegGuheert · January 2011

Surrette confirms low limits for bulk current rates.

Cariboocoot wrote: »

As a rule, the upper charge limit is 13% of the 20hr Amp hour capacity.

I spoke with Surrette today and they informed me that their current recommendation for bulk charging is not to exceed 15% of the 6 hour rate. For the 12 CS 11P battery, that comes to only 38 A!

Here is the exact quote from their current manual:

Bulk Charge
The first part of the charging process is the bulk charge; this is when the maximum amount of current flows into the battery bank until a desired voltage is reached. The recommended maximum current is 15% of the AH Capacity of the battery bank based on the 6 hour rate. A lower current can be used, but this will prolong the charging time. Bulk charge voltage set points are outlined in Table 2.

It seems that Surrette has moved a LONG way from the bravado of some of their literature:

Rolls / Surrette Batteries are designed with thick plates, high density active material; for cycling service and to minimize the impact of heavy charging. These two design parameters, coupled with other design features, require more lead per unit which increases battery life in high cycle applications.

and

In most alternative energy applications, maximum charge application is only available for 6-8 hrs. Meaning, the majority of charging has to be completed during this time frame to avoid reliance on an auxiliary generator further reduction in the battery’s state of charge (SOC).

So instead of being able to size the battery and array around the application, you need to size the array for the application and then *oversize* the battery by a large margin because Surrette makes them too fragile to meet the application requirements, even though they call them "Solar Batteries".

I now have several different documents from Rolls, all with quite different recommendations for how to charge and discharge their batteries. Unfortunately, NONE of these documents have dates or revision numbers on them of any kind. As such, you cannot tell which is the most current or which may replace the others. This is compounded by the fact that they do not make their documents freely available without providing private information but other documents by them are available elsewhere on the internet. I complained to them about this lack of version/date information. It is unbelievable that they still do not have any kind of revision control on their customer-facing documents.

Given the price of these things, I'm inclined to tell my sister that Surrette batteries are just as fragile as the other alternatives out there, but that they can provide long warrantees because they make you buy twice the battery that is needed. Perhaps it is simply better to buy cheaper batteries and plan on replacing them more often.

niel · January 2011

Re: Please recommend a charge controller for this system...

very revealing development.

RegGuheert · January 2011

Re: Please recommend a charge controller for this system...

We've decided to switch to Sun Xtender PVX-4050HT batteries, which have a similar price and a similar 24-hour capacity, but much higher capacity at high discharge rates. They can handle much more bulk charge current than we will have available. In fact, the manufacturer requirements are somewhat *opposite* of the ones from Surrette:

The charging current during Bulk stage should be set as high as practical; higher current levels mean faster recharge time. For repetitive deep cycling, chargers should have an output current of at least 0.2C (20 Amps for a 100 Ah battery). If the output current is less than this value, the cycle life of the battery may be negatively affected. Due to the low impedance design, Sun Xtender batteries can tolerate in-rush current levels as high as 5C (500A for a 100Ah battery).

As such, we will now end up on the opposite end of the equation where we will be on the low end of the available charge current. I'll take that risk, since we will be spending less than half of what Surrette wants to handle this array. Yeah, these batteries may not last as long as the Surrettes, but given all the failure modes possible with flooded batteries, they may just last LONGER. We will have to decide if we were satisfied with them when it comes time to replace them.

niel · January 2011

Re: Please recommend a charge controller for this system...

you may be surprised at the performance of the agms. they charge more efficiently and you will find it will do just fine at various charge rates.

my original pvx1040t is 7+ years old and is still doing fine. it even had a few outgas moments when i was manually charging it with a standard automotive charger that had no regulation and i forgot to look in on it in a timely fashion. i'm sure it cost me a bit of capacity, but not much. due note that it is not one of the pvx1040t batteries i list in my sigline.

keep us updated on your observations.

Dave Angelini · January 2011

Re: Please recommend a charge controller for this system...

Wish I had time, I don't... I would check some of the numbers in this thread. Good Luck !

RegGuheert · January 2011

Re: Please recommend a charge controller for this system...

niel wrote: »

you may be surprised at the performance of the agms. they charge more efficiently and you will find it will do just fine at various charge rates.

my original pvx1040t is 7+ years old and is still doing fine. it even had a few outgas moments when i was manually charging it with a standard automotive charger that had no regulation and i forgot to look in on it in a timely fashion. i'm sure it cost me a bit of capacity, but not much. due note that it is not one of the pvx1040t batteries i list in my sigline.

keep us updated on your observations.

Thanks for that information, Niel! That is very encouraging! It is good to have some real experiences upon which to base a decision.

Currently it is between the Sun Xtender PVX-4050HT and the Surrette SG-460AGM. She needs to deal with a particular vendor since she has already paid for flooded batteries from them. The trade seems to be as follows:

- Surrette SG-460AGM has a lower price and a better warranty and is in stock.
- Sun Xtender PVX-4050HT has lower resistance so it has markedly higher capacity at higher discharge rates. As such, it will sustain a lower DOD for a given load current profile than will the Surrette. Given that their cycle-life curves look virtually identical, this would indicate the Sun Xtender should have a longer life in the same application.

niel · January 2011

Re: Please recommend a charge controller for this system...

that will be your decision to come to by weighing the pros and cons between the 2 different agms in question. i have never owned or are familiar with surrette's agms to say anything other than that they are agms so i can't compare them both for you through experience.

RegGuheert · February 2011

Re: Please recommend a charge controller for this system...

niel wrote: »

my original pvx1040t is 7+ years old and is still doing fine. it even had a few outgas moments when i was manually charging it with a standard automotive charger that had no regulation and i forgot to look in on it in a timely fashion. i'm sure it cost me a bit of capacity, but not much. due note that it is not one of the pvx1040t batteries i list in my sigline.

Since you have had good success with the SunXtender batteries and have even chosen them again for your newer system, I am hopeful that you will answer a few questions about your experiences with them for me.

1) You mentioned that you had "a few outgas moments" with the old battery. Can you tell me how you knew? Is it clearly audible? What was the voltage when it happened?

2) Can you tell me what type of charge regime you have used for the single PVX1040T that is over seven years old? Type of controller? Nightly DOD? 2-stage or 3-stage? Bulk stop voltage? How is absorb terminated if 3-stage? Float voltage?

3) With your new system I see you are using 4 PVX1040Ts with a Classic 150. Do you have a 24V system or a 48V system? How do you have the Classic set up to charge them? What has been your experience with that?

4) When you bought your 4 PVX1040Ts, did they have a very similar voltage on them or did you observe differences? We've seen a difference of about 0.1 V on the 6V batteries which we received, even though they are all consecutive serial numbers. Three batteries are lower than the rest and they clearly have a lower state-of-charge given that the others clearly reached full charge before these three. That seems a little odd given that these are supposed to have such a low self-discharge rate and I *think* they were manufactured very recently.

5) If you saw different voltages, were you able to bring them to the same voltage eventually, or did the differences remain? To avoid any damage, I'm planning on just running these on float for a while until they even out, but I'm wondering if there is a simpler way. We are not in a hurry, so any approach is fine for us.

6) Do you believe you will be able to get as much life out of a bank of four batteries as you did out of a single one?

Thanks in advance!

Reg

ETA: It looks like your inverter is 12V, so perhaps you didn't see any differences in the battery voltages. In the case of four batteries in parallel, do you have any way to know if they are getting fully charged occasionally?

RegGuheert · March 2011

Re: Please recommend a charge controller for this system...

RegGuheert wrote: »

4) When you bought your 4 PVX1040Ts, did they have a very similar voltage on them or did you observe differences? We've seen a difference of about 0.1 V on the 6V batteries which we received, even though they are all consecutive serial numbers. Three batteries are lower than the rest and they clearly have a lower state-of-charge given that the others clearly reached full charge before these three. That seems a little odd given that these are supposed to have such a low self-discharge rate and I *think* they were manufactured very recently.

I did some calculations based on manufacturer's data and came to the conclusion that a 0.1V difference in discharge voltage in these batteries corresponds to about 80 Ah! Since the Classic currently cannot properly perform any absorb period in this system, all we have right now is bulk and float. At a float current of about 0.5 A, this difference would require about 160 hours of sunlight to resolve itself.

As a result, we started to think about possible remedies and settled on the idea of shutting down the system and repurposing the Classic to charge just the three low batteries, knowing that it goes all the way down to 12V. Unfortunately, after we set this up we discovered that the Classic only charges lead-acid batteries in multiples of 6 cells: 12V, 24V, 36V, 48V, 60V and 72V. Given that, we could not see an obvious way to charge three batteries. and decided to put the system back together.

In the end, I'll need to get the firmware fixed on the Classic and let the batteries spend an hour or two each day in absorb until things are evened out.

Beyond that, I can't think of a simpler solution without transporting the batteries to another location, which is not an overly attractive thing to to given their size and weight.

RegGuheert · March 2011

Re: Please recommend a charge controller for this system...

With some guidance from Ryan at MidNite solar I learned that *any* voltage between the range needed by 12V to 72V batteries can be programmed into the Classic 200, so I headed back over to set it up to charge the three batteries that are low. When I first tried I was frustrated because I again hit the limits of working within ranges around multiples of 12V, which would NOT get me to the 21.6V I needed to charge three batteries. So I completed setup in the wizard for a 12V battery and then went into Charge->Volts and I was able to set any voltage for Absorb and Float that I wanted. Success!

I also set the absorb time above zero since MidNite says the bug I had only applied at 48V. I'll have the homeowner watch these three batteries closely tomorrow to make sure none of them get too high in voltage.

My calculations tell me that it will only take one sunny day to bring these three batteries up to full charge, so tomorrow I will go back out to rejoin them with the others.

I must say I'm impressed that I can do this with a charger I bought to charge a 48V battery. The Classic is proving to be very flexible!

niel · March 2011

Re: Please recommend a charge controller for this system...

sorry for not answering your questions sooner as i had pressing personal business for nearly a week.

1> yes, i heard it bubbling and a small hiss and it wasn't very loud. this was when i was at the absorb stage and if memory serves i was at 14.4v or so. this most likely happened a few other times too so i backed down the voltage to about 14.3v.

2> i have used various charge controllers and even some automotive chargers that i watched while it charged. i have had the simple pwm sunsavers and had one blow out while charging from an ac charger that failed and sent 120vac down the line and one i wired backwards and that blew it out. i have a rv power products (blue sky now) sb50 mppt controller and this operated most of the years. i tweaked the wrong pot inside and couldn't bring it back into line properly, but i didn't try too hard as i now have a c40 on it. this waivers in its voltage, but suffices i guess. this is only for my older pvx1040t that i have been using primarily for operating my ham radios with. the newer 4 battery arrangement is to be used with the classic, but i lack the proper pv power at this time to utilize it right now. i have 2 64w pvs and one is on the older pvx1040t leaving one for the classic and the 4 paralleled pvx1040ts. btw, it works well with the single pv, but i disconnect it manually when there's insufficient sun. there is a charger built into the mms1012 so i don't need to worry too much about the batteries not being charged.

3> i am presently using a pv for 12v going through the classic to 12v batteries paralleled for the newer system and the other 12v pv going to the c40 and to the 1 12v battery for my radios.

4 and 5> when you buy them the voltage can vary. it depends on when the last boost charge was given to them. if they are off you can set them up for 12v and charge 2 at a time in series for 6v batteries to bring them equal in the beginning. afterward they can be as you wish and given a small boost as a whole battery system..

6> sure, why not?

as to paralleled batteries being measured for equal voltage, the only way to do that is to disconnect them from each other and measure their voltage. this is probably a good thing to do once in awhile to be sure there aren't any failures occurring such as a failed wire, connector, or even a cell in one of the batteries. batteries in series can easily be measured. if you find a battery that is lower then switch it with the highest voltage battery. that is physically eqing.

hope this helps.

RegGuheert · March 2011

Re: Please recommend a charge controller for this system...

niel wrote: »

sorry for not answering your questions sooner as i had pressing personal business for nearly a week.

Thanks for answering! I only PMed because I thought perhaps you had missed it. I hope all is well...

niel wrote: »

1> yes, i heard it bubbling and a small hiss and it wasn't very loud. this was when i was at the absorb stage and if memory serves i was at 14.4v or so. this most likely happened a few other times too so i backed down the voltage to about 14.3v.

O.K. That's a little scary! I had two batteries at close to 7.5V the other day when the Classic failed to terminate absorb. I didn't notice any bubbling, heating or hissing, though.

niel wrote: »

2> i have used various charge controllers and even some automotive chargers that i watched while it charged. i have had the simple pwm sunsavers and had one blow out while charging from an ac charger that failed and sent 120vac down the line and one i wired backwards and that blew it out. i have a rv power products (blue sky now) sb50 mppt controller and this operated most of the years. i tweaked the wrong pot inside and couldn't bring it back into line properly, but i didn't try too hard as i now have a c40 on it. this waivers in its voltage, but suffices i guess. this is only for my older pvx1040t that i have been using primarily for operating my ham radios with. the newer 4 battery arrangement is to be used with the classic, but i lack the proper pv power at this time to utilize it right now. i have 2 64w pvs and one is on the older pvx1040t leaving one for the classic and the 4 paralleled pvx1040ts. btw, it works well with the single pv, but i disconnect it manually when there's insufficient sun. there is a charger built into the mms1012 so i don't need to worry too much about the batteries not being charged.

Wow! You been around the block with charge controllers, haven't you!

I have a few RVPP SB3048s here. They were great controllers when they came out. It appears the Classic may be the new king for a while. What a versatile product!

niel wrote: »

3> i am presently using a pv for 12v going through the classic to 12v batteries paralleled for the newer system and the other 12v pv going to the c40 and to the 1 12v battery for my radios.

It's cool that you can do what you need with a 12V system! You must be pretty fond of that inverter! (I'm a little afraid to ask which inverters you have used, given your charge controller history and the large number of 12V inverters I have lying around here!

)

niel wrote: »

4 and 5> when you buy them the voltage can vary. it depends on when the last boost charge was given to them.

This is what I don't get. These are AGMs and the leak rate should be about 1%/MONTH, so I don't see how I can have three batteries down by 20%. Plus, if I'm reading the consecutive serial numbers correctly, it appears they were all made in January. It's almost like the manufacturer just failed to charge those three properly.

niel wrote: »

if they are off you can set them up for 12v and charge 2 at a time in series for 6v batteries to bring them equal in the beginning. afterward they can be as you wish and given a small boost as a whole battery system..

Thanks, Ryan helped me figure out how to charge the three low ones. It is forecast to be sunny all day, so I'm expecting they will be get caught up and I will be able to put the system back together this evening.

niel wrote: »

6> sure, why not?

Well, for reasons like the issue I am having with three of the batteries. Ignoring the issue I had with the Classic, if I had just put them together a string and turned them on (as I SHOULD have been able to do), it's clear that a couple of the fully-charged batteries would have been well-cooked, shortening their life. The thing about separate batteries is that they are never *exactly* the same in terms of chemistry, temperature environment and history. When you put them in a large string those small differences can turn into large problem is one battery gets fully charged or fully discharged before the rest. In a single battery, the cells tend to have better matching in terms of chemistry, environment and history.

We'll see how it goes. I'd be thrilled if we get seven years out of these things!

niel wrote: »

as to paralleled batteries being measured for equal voltage, the only way to do that is to disconnect them from each other and measure their voltage. this is probably a good thing to do once in awhile to be sure there aren't any failures occurring such as a failed wire, connector, or even a cell in one of the batteries. batteries in series can easily be measured. if you find a battery that is lower then switch it with the highest voltage battery. that is physically eqing.

It seems like a trade off: While you can more easily *measure* batteries in series, I think it is much easier to have them get into damaging conditions than in parallel, but that may just be my bias. Certainly having one battery with lower or higher capacity in either arrangement can be quite hard on it.

niel wrote: »

hope this helps.

It really does! It's nice to have someone else here with a Classic/AGM combination with whom I can compare notes. Thanks again for taking the time to answer me!

Reg

RegGuheert · March 2011

Re: Please recommend a charge controller for this system...

niel wrote: »

1> yes, i heard it bubbling and a small hiss and it wasn't very loud. this was when i was at the absorb stage and if memory serves i was at 14.4v or so. this most likely happened a few other times too so i backed down the voltage to about 14.3v.

RegGuheert wrote: »

O.K. That's a little scary! I had two batteries at close to 7.5V the other day when the Classic failed to terminate absorb. I didn't notice any bubbling, heating or hissing, though.

Unfortunately, I got to learn what venting sounds and smells like first hand today. While the Classic set points ARE adjustable over a very wide range, I learned that it is fully capable of ignoring your settings and charging at other voltages instead. When I programmed three 6-V batteries to charge at 21.6 volts the Classic promptly pushed them up over 25.6V and they were bubbling and hissing furiously. Fortunately I was right there and this only continued for about two minutes. One thing I will say about the venting I saw today: there was NO heat involved. Somehow I had always imagined heat.

After a frantic call to MidNite they were able to duplicate the problem. After some head scratching on their part they were able to determine the cause of the problem. It turns out that if you are doing temperature compensation on your batteries, there are upper and lower limits which are separately enforced, so if you set absorb or float outside those limits, your settings are COMPLETELY IGNORED. So be careful if you are charging an odd number of 6V batteries with a Classic controller and be sure to adjust your temperature-compensation limits to include the operating voltages you are using. I had no idea there even were limits on the temperature compensation! MidNite says they will work to change the firmware to try to prevent this problem in the future.

Thanks for your assistance with this Ryan and boB!

Please recommend a charge controller for this system...

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