New system 24 or 48 volt?

yeahgofigure · March 2013

Am in the process of ordering system parts for my cabin in a small off grid community in the mountains near Las Vegas. My installer has me going with a 24 volt setup with a Xantrex XW4024 inverter, Xantrex XW MPPT charge controller, six 235 watt panels, and 24 6V flooded batteries. Am a novice at power but asked why not do 48 volt system since should be more efficient and 48 volt inverter is same price, however my installer said it wouldn't work as it wouldn't charge the batteries properly. He would have to tie the panels together halving the amps which he said meant I'd have to double my array size to 12 panels to get it to charge properly. After a very long talk he said he could do it as 48 volts if I insisted but he insists it wouldn't work. He's done most of the systems in the local community of 70 off grid homes.

My rudimentary understanding is twice the volts means half the amps but same watts/power, so why would the batteries not charge properly? He referred to a gas tank analogy where I'm effectively doubling the size of my gas tank while feeding it half as much gas (amps). Does it have to do with 48V battery arrangement of 3 strings of 8 each versus 24V of 6 strings of 4 each means each string needs 2x the amps? I don't get it as figured power / watt hours should be same no matter if 48V at half the amps and the efficiency of 48V should yield better. I'm not getting it, can anyone shed more light on this?

vtmaps · March 2013

Re: New system 24 or 48 volt?

yeahgofigure wrote: »

and 24 6V flooded batteries.

Welcome to the forum,

In a 24 volt system, 24 6 volt batteries means 6 parallel strings. Multiple parallel strings is a bad idea. You could take those same 24 batteries and configure them in three parallel strings in a 48 volt system.
Your installer is wrong! read: http://forum.solar-electric.com/showthread.php?14674

Next issue is do you have enough panels to charge those batteries (at either 24 or 48 volts)? That depends on the batteries... more info please, brand and model, or at least tell us the capacity of the batteries.

--vtMaps

Photowhit · March 2013

Re: New system 24 or 48 volt?

Either your not understanding something or your installer is an idiot and you need to pass along the experience with the others there and fine some one else to work with you.

Perhaps he or you... Thinks you'll charge at 48 volts and use as 24 volts? This doesn't work. I couldn't come up with anyother senerio that any sensible experienced installer wouldn't want you to move to a 48 volt system. Indeed, I would hope they would have discussed using a forklift taction battery, which, while hard to move around might cost about the same price and would have an expected life of 15 years rather than 5 years.

I guess I'm assuming 6 volt Flooded Lead acid (FLA) golf cart batteries? at 220 amp hours each 6 strings would be 1320 Amphours at 24 volts or 660 Amphours at 48volts (31.68 Kwhours at a 20hr rate for either) Batteries like to be charged at 5-13% of capacity. Your 6 - 235 watt panels or 1410 watt array has a Normal Operating Cell Temprature(NOCT) value of @1150 watts so your max charging rate is around 3.6 percent if everything else had no losses. So you will need to have other means of charging the battery on a regular basis.

In comparison I have a 24volt system with a 800 Amp Hour battery and a 4000 watt array. I would have gone 48 volt but already had the battery, a forklift/traction battery.

While it's nice to keep the componets in the same family, I don't think there is a better charge controller than the Midnite Classic. It's a has several nice features for someone who wants to get their hands dirty and be more involved with their system and some for people who just want their system to work. Later this year they intend to have a battery monitor which will measure the charge current across a shunt. This will allow for the most accurate charging while the system is under load. it also has a feature that allows the charge controller to start loads dependent on the batteries state of charge. so as the batteries near being fully charged you can start a water heating element, or perhaps an airconditioner (if you had a larger array)

mikeo · March 2013

Re: New system 24 or 48 volt?

So you have about 1500 watts worth of solar panels, if you never expect to expand the system, then a 24 volt system is about right. If you ever want to expand over about 2000 watts, then I would suggest going 48 volts now. You have way too many cells on your battery bank for both maintenance purposes and wiring concerns. I would suggest starting with higher capacity batteries for both easier maintenance and longer battery life. Eight L16 400 amp hour batteries would be a much better choice for this system. You only have two parallel strings of 4 batteries and 24 cells to check and keep water in. This would give you around 800 amp/hours capacity and a 5% charge rate under full sun. Even better would be a 800 amp hour 24 volt fork lift style battery, with only 12 cells to maintain. These can be found refurbished from larger industrial battery suppliers at 50% of new price. We have spoken nothing about your intended use (loads) as to whether this is a properly balanced system or not for you.

niel · March 2013

Re: New system 24 or 48 volt?

off hand i don't see a problem in going to 48v and that many battery strings for 24v operation is not a good idea. you have 6 pvs and most likely the installer is going with 2 pvs in series (assuming 60 cell variety of pv) at a minimum per string to feed the controller. this is the smallest number of pvs in a string to charge at the 24v battery voltage. 3 in series works as well as the voc should not exceed the controller's max operational voltage for most 60 cell pvs. in going with the 48v battery voltage you will have to go with 3 pvs in series per string to insure enough voltage to charge the batteries and with 6 pvs this is 2 strings of 3 in series which works out well for you.

in my opinion you will most likely want to expand on the pvs anyway with the large capacity battery bank as i believe it will be marginally acceptable with 6 pvs and this is irregardless of the battery voltage configuration. i would recommend another string of pvs be used regardless of your battery bank config choice.

although an xw cc should work they have some problems in their reliability due to software glitches. the 140v max operating voltage should not be a concern with the xw either for most pvs up to 3 in series, but if in doubt the classic 150 does have the higher operating voltage of 150v and a safety feature on going overvoltage called hypervoc. you will have more bells and whistles with a classic as well as expandability, but more importantly you'll have better service with midnite should you ever require it. same issues appear on the xw inverters as they have good hardware, but are lacking some with software errors if memory serves correctly. getting help from xantrex has been problematic for many. midnite does not have any inverters available at this time as they are still in development.

Cariboocoot · March 2013

Re: New system 24 or 48 volt?

The question is really: do you need a 48 Volt system?
They are somewhat more efficient than 24, but there are problems with handling the higher Voltage.

On the other hand so far he's picked a Xantrex XW inverter (more money spent than is necessary) and a Xantrex XW charge controller (not the best choice) and he doesn't seem to be able to explain things to you in a satisfactory manner.

A few threads worth looking at:
http://forum.solar-electric.com/showthread.php?6136-Glossary
http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power
http://forum.solar-electric.com/showthread.php?16241-Different-Panel-Configurations-on-an-MPPT-Controller

My advice is to familiarize yourself with the system and terminology in general; if you're going to use it, you'd better understand it.

yeahgofigure · March 2013

Re: New system 24 or 48 volt?

Cariboocoot wrote: »

On the other hand so far he's picked a Xantrex XW inverter (more money spent than is necessary) and a Xantrex XW charge controller (not the best choice)

The guys in the local community swear by Xantrex as they've used them almost exclusively with good reliability whereas said anyone that's tried other brands there failed after a few years. Went with 240 volt AC inverter for various reasons and after pricing around only seems to be about $300 more than a couple other comparable 240V similar watt inverters. What other 240V inverters and MPPT controller options should I look at?

vtmaps wrote: »

Next issue is do you have enough panels to charge those batteries (at either 24 or 48 volts)? That depends on the batteries... more info please, brand and model, or at least tell us the capacity of the batteries.

24 Trojan T-105 6V 225ah batteries. I know some guys might not like the choice so please let's not go off topic, the locals have good experience with them for the price and say many have over 10 years on theirs as long as maintain them properly.

Cariboocoot · March 2013

Re: New system 24 or 48 volt?

Were it me, I'd have picked a MidNite Classic controller and Magnum inverter.

Nothing wrong with Trojan batteries, really, providing you pick the right ones for an RE application and don't mind paying the price.

Here's the thing about the array size vs. system Voltage: with battery capacity of equivalent power, the same size array is needed to recharge it. Only the ratios change.

Example, using theoretical batteries and leaving out losses because we're only explaining the principal here:

Take four 12 Volt 100 Amp hour batteries. Connect in series/parallel for 200 Amp hours @ 24 Volts = 4800 Watt hours.
Connect all four in series for 100 Amp hours @ 48 Volts = 4800 Watt hours.
Same batteries, same power.

Now to recharge them we can use the 10% capacity rule-of-thumb shortcut (and leave out the derating as we only need to compare delivered Watts).

20 Amps @ 24 Volts = 480 Watts
10 Amps @ 48 Volts = 480 Watts

Same power in both battery banks = same size array to recharge. You only configure the array differently, so that the Voltage is higher and can meet the charging level. The higher Voltage is more efficient and has less line loss. Since the controller is an MPPT type it would have no difficulty with either configuration.

If your installer doesn't understand this, he shouldn't be doing the job.

yeahgofigure · March 2013

Re: New system 24 or 48 volt?

Originally had 8 panels with 2 non-MPPT controllers but when decided to pony up for MPPT we thought dropping to 6 panels to keep under controller max amps and voltage can do with just one controller. Later if need would expand to 8 panels and 2nd controller. But looking at specs it says 140V and 60amp max, so if I go 48V DC does that mean I can go 8 panels on single MPPT controller?

Photowhit · March 2013

Re: New system 24 or 48 volt?

yeahgofigure wrote: »

The guys in the local community swear by Xantrex as they've used them almost exclusively with good reliability whereas said anyone that's tried other brands there failed after a few years. Went with 240 volt AC inverter for various reasons and after pricing around only seems to be about $300 more than a couple other comparable 240V similar watt inverters. What other 240V inverters and MPPT controller options should I look at?

I use a xantrex/Prosine inverter and am happy with it, Magnum make a 4024 that is a 4000 watt 120/240 inverter and they make a 4448 that is a 4400watt 48Volt inverter. They start start around $2000. I've read that there are some added equipment/tools needed for the xantrex at least for trouble shooting. This is a forum, so it's likely that the Xantrex is a good product and we have just heard about the problems.

I think there is no other choice at this point in the charge controller maker than the Midnite classic. The people there started with Xantrex, then developed products at Outback, and now own and run Midnite. They have a long history in the renewable field. The "Waste Not" feature starting loads when the charge controller reaches a point in it's charging cycle (cobbled together by others using voltage sensors) and allows for less waste in an off grid system. This combined with the charge controller knowing the true charge going into the battery bank via the shunt rather than trusting what information it can gather at the charge controller, will make for better charging while loads are present.

yeahgofigure wrote: »

24 Trojan T-105 6V 225ah batteries. I know some guys might not like the choice so please let's not go off topic, the locals have good experience with them for the price and say many have over 10 years on theirs as long as maintain them properly.

I have no problem with Trojan batteries, they are fine products and from reports I've heard they are likely to last longer than generic batteries. I would think that expecting more than 7 years out of any Golf cart sized batteries would be foolish, and with that many cells you might fine a laarger traction battery an advantage in maintanance and longevity as well as cost.

Blackcherry04 · March 2013

Re: New system 24 or 48 volt?

The problem with Xantrex is that they are not setup to handle service at the Consumer level. The Dealer / Installer and Distributor / Service Center level has no issues with them. They have all the direct phone numbers and will have the right people give you the answer right away. This becomes a issue for Internet buyers where the products come out of the normal Xantrex Distribution channels and they want service. NAWS may be a exception and a few others, but with e-bay and others, your on your own or get into the call line. Another consideration is their " all on one board inverters" are throw aways, when the warranty runs out, throw it in the trash if you have a problem.

Photowhit · March 2013

Re: New system 24 or 48 volt?

In a 24 volt system the Midnite classic can handle up to 96 Amps, I think that makes up to a 2500-2600 watt array practical, remember that the array will produce roughly 80% in most situations, other than cold sunny days.

They have a sizing tool here.

The classic 150 will handle up to 150 volts in coming and has the added ability to shut down if above the 150 volts but less than 174 volt (hyper VOC?) with out harming the charge controller. VOC can rise on cold days and their sizing tool will take into account the coldest temp in your area. This protects panel on those cold mornings and the sun warms the panels the VOC will drop and the charge controller will start functioning properly.

Charge controllers work on amperage, so if you double the voltage to 48 volts you can double the wattage of the array it will handle, though the classic has slightly different paramiters for 48 volt use I think the max is 84 amps so figure about 4000 watt array as max. the sizing tool will help with this.

Cariboocoot · March 2013

Re: New system 24 or 48 volt?

yeahgofigure wrote: »

Originally had 8 panels with 2 non-MPPT controllers but when decided to pony up for MPPT we thought dropping to 6 panels to keep under controller max amps and voltage can do with just one controller. Later if need would expand to 8 panels and 2nd controller. But looking at specs it says 140V and 60amp max, so if I go 48V DC does that mean I can go 8 panels on single MPPT controller?

Those numbers are on two different sides of the controller. The 140 Volt maximum is on the input: the Voc (not Vmp) of the array can not exceed 140 Volts. The 60 Amps is on the output and applies to any system Voltage level. So 60 Amps @ 12 Volts is approximately 720 Watts of array, but on 24 Volts it is 1440 Watts and on 48 it is 2880. What's more, if you were to "over panel" an MPPT controller it will simply "clip" (lose) the additional power and limit output to its maximum current capacity. Six 235 Watt panels is 1410 Watts, eight is 1880 so yes you probably would not put eight on a 60 Amp controller @ 24 Volts. A MidNite Classic would handle all of them, btw, as it is an 80 Amp controller (1920 Watts @ 24 Volts).

mikeo · March 2013

Re: New system 24 or 48 volt?

The reply to your previous question is that YES you can run twice the watts in panels at 48 volts through a 60 amp controller vs 24 volts through a 60 amp controller, which is why I said before if you aren't going to expand with what you are starting, then 24 volts will be fine, otherwise go to a 48 volt system now. 8 x 235 watt panels would be 1880 watts and 67 amps at 24 volts. So you would need an 80 amp controller, either Outback FM80 or Midnight MPPT controllers. But with a 48 volt system, 1880 watts is at 1/2 the amps or 34 amps which would work with the 60 amp Xantrex MPPT controller or Outback FM60 controllers. If you look at my system in my Sig below, you will see I have a 24 volt system working at its upper limit. I have zero room to expand except to add another array and another controller, ore replace my FM60 with an 80 amp would give me just a little expansion. ON the other hand had I started at 48 volts, I could have just doubled the array.

Photowhit · March 2013

Re: New system 24 or 48 volt?

I admit to being a fan of the Midnite Classic, since it has so many features that we forget some of them...

If you have to have a second charge controller, the Classic allows the charge controllers to work together and comunicate with each other with it's "Follow Me" feature making things a little simpler, one Battery Temperature sensor, one link to the shunt...

Here's a link to the Midnite site info on the 150.

Don't let the $850 price scare you the Classic 150 at Northern Arizona Wind and Sun runs $610 and the Classic Lite without the LCD display runs $500

ChrisOlson · March 2013

Re: New system 24 or 48 volt?

Cariboocoot wrote: »

Those numbers are on two different sides of the controller. The 140 Volt maximum is on the input: the Voc (not Vmp) of the array can not exceed 140 Volts.
........A MidNite Classic would handle all of them, btw, as it is an 80 Amp controller (1920 Watts @ 24 Volts).

The XW MPPT60-150 can actually handle 150 Voc and 140 maximum operating voltage. I just bought one a few days ago and hooked it up to our new 1 kW array. I actually like the controller - it was easy to set up, interfaces nicely with our XW Power System and SCP and seems to work fine.

The Classic can put out 94 amps on 24V. But if it's above 70 degrees in your utility room it will quickly heat up and de-rate itself to in the 80's. I used to have no problems getting 2,600-2,700 watts out of the Classic 150 on our 24V system with 3 kW installed capacity on it.

I also see nothing wrong with the 24V system vs 48. There's no real advantage to going to 48V on a system at 4 kW size when you got MPPT controllers on the power sources. However, the XW4024 is a brute of an inverter for a cabin, for pete's sake. You could probably put in a lighter duty one like a Magnum and save a little money if the only thing you need 240V split phase for is a well pump. The Magnum inverters use a high temp rated transformer so they're smaller and lighter. But they're also less efficient than the XW. And if you're intent on getting the XW MPPT controller, then the XW would probably be a better choice because it integrates with the system.

But as far as the idea of going to 48V on this system? I'd say forget it and stick with the 24V.
--
Chris

yeahgofigure · March 2013

Re: New system 24 or 48 volt?

Maybe cabin is a misnomer as is 1300 sqft, one bed, loft, 2 bath, no well pump (hoa provided water), 16 cuft energy star fridge, microwave, dishwasher, washer, propane dryer, 2 tvs, accessories, 2 adults, 3 kids. After running #s came up with about 6 to 8kwh per day and probably visit 30 to 60 days per year. Community is completely off-grid no public power, gas, etc. Winter is typically 10 low to 40 high and summer 60 lows to 90 high maxing around 100 on really hot days. Figure the equipment shed could run even warmer inside during summer.

My main concern seems that a lot of peeps are saying I don't have enough panels to charge the batteries properly, no matter is 24 or 48 volt system. Sort of understanding this more now, just wondering if 8 panels would do me better and if did that sounds like I'd need to go 48 volts so don't have to get another charge controller plus 3 strings of 8 batteries each versus 6 strings of 4 each sounds like would give less equalization issues.

ChrisOlson · March 2013

Re: New system 24 or 48 volt?

yeahgofigure wrote: »

Maybe cabin is a misnomer as is 1300 sqft, one bed, loft, 2 bath, no well pump (hoa provided water), 16 cuft energy star fridge, microwave, dishwasher, washer, propane dryer, 2 tvs, accessories, 2 adults, 3 kids.

Yeah, Go Figure

That would actually probably be a good match for a 4024.

sounds like I'd need to go 48 volts so don't have to get another charge controller plus 3 strings of 8 batteries each versus 6 strings of 4 each sounds like would give less equalization issues.

I doubt you'll have much problems with parallel'd strings. We run 6 parallel strings here and not a single issue with it. And in fact, if you want to get the Big Amps to your inverter to run it at full load without huge voltage sag from the bank, you'll need parallel strings anyway. Total amps to the inverter divided by number of parallel strings equals the amps each string has to deliver to the load. Take a single series string and try to pull 180 amps from it - then get back to me and let me know what happens (I already know). Then put six of those strings in parallel and pull that same 180 amps from the bank and watch how the voltage to the inverter barely sags at full load with each string only delivering 30 amps.

After completing the above exercise you will gain a better understanding of what it takes to power a big inverter at full load from batteries.

I'd say the 24/48V issue is a non-issue either way. You can easily fix having to buy another charge controller for more panels on 24V by just buying a Classic 150 instead of the XW-MPPT60-150.
--
Chris

Cariboocoot · March 2013

Re: New system 24 or 48 volt?

Let's run the numbers the right way: from the loads.

8kW hours a day? Quite a lot of power by off grid standards. My place uses about 1/3 that. With water pump and microwave.

Anyway: 8000 Watt hours on 24 Volts = 334 Amp hours = 668 Amp hour minimum battery size.
Yes, this is in the power area where you could benefit from a 48 Volt system. Although I'd start by trying to get that consumption number down. Teach people about 'OFF' would probably do to begin with.

668 Amp hours could just squeak through on 60 Amps charging and the previously mentioned 1880 Watt array (all eight 235 Watt panels to deliver a real 60 Amps maximum current after derating).

It's kind of a close-run thing. If you've already got the 24 Volt inverter it can be made to work.

ChrisOlson · March 2013

Re: New system 24 or 48 volt?

Cariboocoot wrote: »

8kW hours a day? Quite a lot of power by off grid standards. My place uses about 1/3 that. With water pump and microwave.

Yeah but 'coot - that's only an average load of 350 watts. I can understand that. When you have a place like that you go there to enjoy yourself and that means having some conveniences like one TV for the kids and another one for mom and dad. Me and Kristin here used to have dual 4024's with 2,400 amp-hours and 25-30 kWh/day consumption. And not a single issue with it other than having a little more inverter capacity than we actually needed, and the generator was too big.

After we got all MPPT stuff the only difference I could tell between 24 and 48V is how many amps go to the inverter(s) for a given load. And that's just two pieces of wire.

There is no inherent advantage with 48V over 24V with a given battery bank either. Every battery in that bank, regardless of how it's wired, has to deliver the same amps for the same load, regardless of the system voltage. You put eight 6V golf cart batteries in series for 48V and pull 100 amps from it and every battery has to deliver the full 100 amps. Rewire the same batteries series/parallel for 24V and now you got two series strings with four batteries in each string. Pull 200 amps from it (same load on 24V). Each battery still has to deliver 100 amps. Only difference is in the total current going to the inverter.

So I dunno. Once you go to 48V everything gets more expensive. You can't even find relays with 48V coils to turn things on automatically. Or if you want to wire in something that's DC on 24V you can use cheap and readily available SquareD QO boxes and breakers. On 48V you can't. For a part time home? Yeah, I dunno. If it was me I'd go 24V and I guarantee it would work fine because already BTDT with one heck of a lot bigger system than what's being proposed.

The one and ONLY reason we ended up going to 48V here was because we wanted to switch to a single larger inverter. And bigger than 4 kVA is just not available for 24V.
--
Chris

Cariboocoot · March 2013

Re: New system 24 or 48 volt?

Yes 48 Volts can present problems as well as advantages. Most of them to do with handling the higher Voltage. Ironic, isn't it? You go up in Voltage to get away from the troubles of high current and ... different troubles.

I personally like 24 as a nice "compromise" Voltage; eliminates the current troubles of 12 without getting into the Voltage troubles of 48. But sometimes you do have to pick one of the other system Voltages. I don't think this is one of those times. Heck you could make an 800 Amp hour battery bank out of a single string of 2 Volt cells or parallel up some larger 6 Volts et cetera. Even use a forklift battery if you need lots of Amp hours on hand.

Incidentally, the parallel battery problems are not so noticeable with high system Voltages as the minute changes in resistance between strings has less effect.

Have I mentioned this in this thread yet: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power

ChrisOlson · March 2013

Re: New system 24 or 48 volt?

Cariboocoot wrote: »

Incidentally, the parallel battery problems are not so noticeable with high system Voltages as the minute changes in resistance between strings has less effect.

Yessir. That is true.

In this case, I believe the XW4024 would be a good choice over a Magnum. If the system ever needs to be expanded capacity-wise the generator can increase the capacity for the intermittent big load that exceeds the inverter capacity by using Gen Support. A Magnum can't do that

Plus I looked at the price on NAWS of the two inverters and they got a REALLY good price on the XW4024 there! $2,376? For only 200 bucks more than a MS4024PAE, definitely get the big one. Sure, the shipping will be quite a bit more, but IMHO the XW is more inverter, and it's more efficient.

But then I see the XW4548 is the same price. Hmmmm..... That throws in an interesting twist.
--
Chris

Photowhit · March 2013

Re: New system 24 or 48 volt?

ChrisOlson wrote: »

Yeah, Go Figure ... you'll need parallel strings anyway. Total amps to the inverter divided by number of parallel strings equals the amps each string has to deliver to the load. Take a single series string and try to pull 180 amps from it - then get back to me and let me know what happens (I already know). ....

While I can't draw that kind of amperage from my fork lift battery, It is designed to discharge over a 6 -8 hour period, don't think it would have a huge problem, though a continuous load of 4400 watts is unlikely for long periods of time. If you plan to run 4400 watts for long periods of time you'll need a much larger system all around.

I wanted to ask about the problems with derating of the Classic at 70 degrees... is this in use with you wind generators?

ChrisOlson · March 2013

Re: New system 24 or 48 volt?

Photowhit wrote: »

I wanted to ask about the problems with derating of the Classic at 70 degrees... is this in use with you wind generators?

No, it's with solar panels. The turbines only put out about 50 amps (3 kW) peak and 40-45A continuous on a good day from each one.

For awhile we had more panels on the Classic than it could handle when we had our 24V system. So it got pushed to it's maximum output every single day and I had the input amps limited to keep it from going over about 2.7 kW. It would get hot and de-rate itself to ~84-86 amps based on its internal temperature.
--
Chris

Photowhit · March 2013

Re: New system 24 or 48 volt?

ChrisOlson wrote: »

There is no inherent advantage with 48V over 24V with a given battery bank either. Every battery in that bank, regardless of how it's wired, has to deliver the same amps for the same load, regardless of the system voltage. You put eight 6V golf cart batteries in series for 48V and pull 100 amps from it and every battery has to deliver the full 100 amps. Rewire the same batteries series/parallel for 24V and now you got two series strings with four batteries in each string. Pull 200 amps from it (same load on 24V). Each battery still has to deliver 100 amps. Only difference is in the total current going to the inverter.

OK Chris, I have a 800 Amp hour 24 v battery, I need a 4Kw array to charg it, so I need 2 Charge controllers, if I had a 400 Amp hour 48 v battery I would need 1 charge controller... would that be an advantage?

ChrisOlson · March 2013

Re: New system 24 or 48 volt?

Photowhit wrote: »

OK Chris, I have a 800 Amp hour 24 v battery, I need a 4Kw array to charg it, so I need 2 Charge controllers, if I had a 400 Amp hour 48 v battery I would need 1 charge controller... would that be an advantage?

Not to my way of thinking. An 800 amp hour bank only needs 80 amps for bulk. You can put 4 kW on a Classic 150 with no problem and it just won't use the maximum capacity on a good day. But it will probably easily put out 80 amps on a more marginal day. So it still works fine and you still only need one charge controller on 24V. We did it that way for over a year, and there was very, very few days that we could've gotten more power out of the array than what the Classic could handle, even though the array was over-sized for it.
--
Chris

Photowhit · March 2013

Re: New system 24 or 48 volt?

ChrisOlson wrote: »

For awhile we had more panels on the Classic than it could handle when we had our 24V system. So it got pushed to it's maximum output every single day and I had the input amps limited to keep it from going over about 2.7 kW. It would get hot and de-rate itself to ~84-86 amps based on its internal temperature.

Thanks, I have 2 with 2kw on each, and they will live outside, in the shade in an box with fan venting, but likely see 100 degree temps, but with increased temps likely to only see 60 amps or so. You didn't seal your classics? I'll likely have 3 by the end of summer with 2 inverters in a 20 cubic foot box. 12" square filtered air intake and a 4" fan out.

Photowhit · March 2013

Re: New system 24 or 48 volt?

ChrisOlson wrote: »

Not to my way of thinking. An 800 amp hour bank only needs 80 amps for bulk. You can put 4 kW on a Classic 150 with no problem and it just won't use the maximum capacity on a good day. But it will probably easily put out 80 amps on a more marginal day. So it still works fine and you still only need one charge controller on 24V. We did it that way for over a year, and there was very, very few days that we could've gotten more power out of the array than what the Classic could handle, even though the array was over-sized for it.

I wouldn't risk it, particularly with them living outside, bank will act larger and I will be drawing lots of wattage as well running a couple A/C units, reason I'm so excited about the battery module, so the battery charging is reasonable well monitored with all the output.

We haven't asked the OP about any A/C usage...
...there was an OP, somewhere near Las Vegas...lol

For the OP, I would have gone with a 48V system, but had already purchased the large traction battery for my cabin, before finding a deal on a Mobile Home and 2+ acres... I figure to use 13-15Kw hours in the summer time, much of it direct. Lucky our heat comes with sun. an 800 Ah 24V battery only represents about a 9Kw of usable storage to 50% this is a tiny amount but I hope it will be fine with the lessened over night demands and heat w/ sun day time usage. The part about the battery module has to do with fully charging a battery while your drawing 1+Kw an hour. For normal charge controller this can be confusing.

mtdoc · March 2013

Re: New system 24 or 48 volt?

Just FWIW - an observation:

I've seen plenty of posters on this and other forums who say "I wish I had gone with a 48 volt system at the start but now it's too late because of all I've invested in my 24V (or 12V) system...."

I've never once heard of someone who went with a 48 Volt system and later regretted it.

vtmaps · March 2013

Re: New system 24 or 48 volt?

ChrisOlson wrote: »

For awhile we had more panels on the Classic than it could handle when we had our 24V system.
<snip>
It would get hot and de-rate itself to ~84-86 amps based on its internal temperature.

Chris, what Vmp were you sending to the Classic? It runs cooler with lower Vmp. --vtMaps

Rngr275 · March 2013

Re: New system 24 or 48 volt?

I am a real "Cherry" to living off grid but I will tell you right now that maintaining 24 batteries is going to suck! These are the heart of your system and you WILL have to watch them very closely to keep them happy. Which equals lots of time spent babysitting or chance ruining them. Just my opinion.

New system 24 or 48 volt?

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