48 volts in 12 volts out...where's teh rest of it going????

Off-grid Texan

I live off-grid east of Dallas. I have two 240 watt panels producing 480 watts very consitantly. I have them wired in parallel giving my Xantrex C40 charge controller 48 volts and about 21 amps to distribute to my 8 battery bank of Interstate 232 amp-hour golf cart batteries wired to a 2000w inverter. When I test with my voltmeter it shows a little more than 12 volts and just under 5 amps going to the battery bank. Where is all the rest of that power going?? I'm a bit befuddled.

I don't know if this is relevant but I'll include it. My batteries won't take more than a 60% charge when charged with a 10-20 amp battery charger hooked to a generator on cloudy days. After researching I learned I need about 60 amps to adequately charge my entire bank.

Thanks

BB.

Re: 48 volts in 12 volts out...where's teh rest of it going????

Welcome to the forum OG Texan.

I am not sure I understand your battery bank... It is 8x 6 volt 232 AH batteries in series (one string) of 48 volts? Or two parallel strings of 4 batteries each for 24 volts @ 464 AH battery bank?

And regarding the solar panels, can we have the exact specifications for them (Vmp/Imp) and if they are two in series or two in parallel.

Your numbers are not quite lining up from what I can see. It would appear that you have a 24 volt battery bank--But I am not sure. And it matters that you match the "optimum" array voltage + PWM controller to the right battery bank voltage or you can have quite a problem (low charging current, or low charging voltages).

Regarding charging your battery bank, we usually recommend 5% to 13% or so for solar charging current... If you have an AC charger (utility or genset), you can go 10-20-25% or so rate of charge.

Anyway, before I confuse you more, I would like to see some more details on your system.

-Bill

bill von novak

Re: 48 volts in 12 volts out...where's teh rest of it going????

Off-grid Texan wrote: »

I live off-grid east of Dallas. I have two 240 watt panels producing 480 watts very consitantly. I have them wired in parallel giving my Xantrex C40 charge controller 48 volts and about 21 amps to distribute

OK problems 1 and 2:
First of, 480 watts divided by 48 (actually about 56 volts during charge) is about 8 amps, not 21 amps.
Secondly, there are very few 48 volt (which means a Voc of about 72 volts) panels out there. So you probably don't have the voltage available to charge that battery bank at all. Did you mean "wired in series?"

to my 8 battery bank of Interstate 232 amp-hour golf cart batteries wired to a 2000w inverter. When I test with my voltmeter it shows a little more than 12 volts and just under 5 amps going to the battery bank. Where is all the rest of that power going?? I'm a bit befuddled.

If your voltmeter is showing 12 volts across a 48 volt battery bank something is very, very wrong. Either the bank is completely and utterly dead, or you are measuring the wrong location, or your bank isn't connected as a 48 volt bank. Most likely the latter two.

I don't know if this is relevant but I'll include it. My batteries won't take more than a 60% charge when charged with a 10-20 amp battery charger hooked to a generator on cloudy days. After researching I learned I need about 60 amps to adequately charge my entire bank.

How are you arriving at the 60% number? (That's too low a charge rate anyway.)

icarus

Re: 48 volts in 12 volts out...where's teh rest of it going????

Do you have the C40 wired/configed for 48 vdc?

Tony

westbranch

Re: 48 volts in 12 volts out...where's teh rest of it going????

I am thinking he has the C40 set for 12 V and he is losing the rest of the power as that is a PWM CC...

Off-grid Texan

Re: 48 volts in 12 volts out...where's teh rest of it going????

I'm sorry I was unclear. Let me clarify. My panels are 240 watts each with an output of 48v and 5'ish amps a piece. They are wired in parallel giving me 48v and about 20-22'ish amps to my charge controller. I know the numbers don't add up in the amp department (5 amps individually but 20 amps when paralleled) but my Fluke voltmeter shows about 20 amps coming in. The battery bank is made up of eight 6v batts wired in series and parallell to give me a 12v bank which the C40 charge controller is set for. The battery charger I spoke of that I use (Schumacher 10A/20A) to charge from my gen never reads higher than a 60-63% charge...ever.

It just seems there is something not right. If I'm bringing in (optimally) 48 volts and 20'ish amps (between the two paralleled 240 watt panels) and only 12.3-12.4v / 4 amps (according to my Fluke) is going to my batt bank it would seem my panels are over kill. I know that's not the case so can someone tell me...am I overlooking something stupidly obvious here?

By the way...my reasoning behind a 12v system is convenience. I have a 12v batt charger and a 12v 2000w inverter. Do I need to go 24v or 48v perhaps? I'm open to all input guys. Thanks!!

Cariboocoot

Re: 48 volts in 12 volts out...where's teh rest of it going????

The C40 is a PWM type charge controller: it can not down-convert the higher panel Voltage into additional charge current for your 12 Volt system. With the set-up the way it is now all you will get is the current rating of the panels passed through to the batteries; an enormous waste of power potential.

Your 240 Watt panels are unlikely to be 48 Volts either, as that would be quite unusual. Panels of that size are typically 30 Vmp.

However that does not change the fact that the C40 cannot do what you are asking it to. For this operation you need an MPPT type charge controller.

jcheil

Re: 48 volts in 12 volts out...where's teh rest of it going????

Off-grid Texan wrote: »

I'm sorry I was unclear. Let me clarify. My panels are 240 watts each with an output of 48v and 10'ish amps a piece. They are wired in parallel giving me 48v and about 20-22'ish amps to my charge controller. The battery bank is made up of eight 6v batts wired in series and parallell to give me a 12v bank which the C40 charge controller is set for. The battery charger I spoke of that I use to charge from my gen never reads higher than a 60-63% charge...ever.

It just seems there is something not right. If I'm bringing in (optimally) 48 volts and 20'ish amps and only 12.3-12.4v / 4 amps is going to my batt bank it would seem my panels are over kill. I know that's not the case so can someone tell me...am I way overlooking something stupidly obvious here? Thanks.

Get (all) the specs from the back of the panels and post them here.
Unless we are missing something, your setup is not going to produce what you are expecting it to produce.
The panels and controller are mismatched and will not give you anywhere near the full output of the panels the way it is now so I am not sure where you are getting those number from. Certainly not the display on the controller (do you have the display?).

If you are using a PWM (c40) controller, it is designed only for "true" 12v, 24v and 48v panels (although I know of no true 48v panels that exist - you would series 4 12v or 2 24v panels).

Off-grid Texan

Re: 48 volts in 12 volts out...where's teh rest of it going????

No, it's wired for 12v. I know I wasn't all that clear in my first post, I apologize, so I reposted for clarification up top.

Off-grid Texan

Re: 48 volts in 12 volts out...where's teh rest of it going????

I don't have a display for my C40, but it is coming soon. All readings I have are solid and obtained from my digital Fluke voltmeter. As for panel specs there are none. I think they're B grade panels. They both produce the same amount of power and are in great shape.

Off-grid Texan

Re: 48 volts in 12 volts out...where's teh rest of it going????

Uhg...ok. So to use my C40 what panels do I need? I can use this in another buidling I have so it's not a waste. What "econimical" MPPT controller would you recommend for my current set up?

Cariboocoot

Re: 48 volts in 12 volts out...where's teh rest of it going????

Off-grid Texan wrote: »

Uhg...ok. So to use my C40 what panels do I need? I can use this in another buidling I have so it's not a waste. What "econimical" MPPT controller would you recommend for my current set up?

Don't change your panels, change your controller.
The panels that would work with a 12 Volt system cost about $2 per Watt so you'd spend like $960 to get the same 480 Watt array. Any top-of-the-line MPPT controller costs about half that!

With 480 Watts feeding a 12 Volt system you'd expect around 30 Amps output so you could use a Rogue 3048 or a MidNite Kid or the Mornignstar TriStar 30 MPPT. All are new 30 Amp MPPT controllers. The MidNite the top quality, and least expensive. You're looking at <$300 for that: http://www.solar-electric.com/midnite-solar-kid-controller-accessories.html

Off-grid Texan

Re: 48 volts in 12 volts out...where's teh rest of it going????

Cariboocoot wrote: »

Don't change your panels, change your controller.
The panels that would work with a 12 Volt system cost about $2 per Watt so you'd spend like $960 to get the same 480 Watt array. Any top-of-the-line MPPT controller costs about half that!

With 480 Watts feeding a 12 Volt system you'd expect around 30 Amps output so you could use a Rogue 3048 or a MidNite Kid or the Mornignstar TriStar 30 MPPT. All are new 30 Amp MPPT controllers. The MidNite the top quality, and least expensive. You're looking at <$300 for that: http://www.solar-electric.com/midnite-solar-kid-controller-accessories.html

So let's say I want to expand my panel array. I can get more of these panels for $100 a piece! I really can't turn that down. Will the 30 amp charge controller wind up being too small later on and at what point does the 30 become too small? How many panels later will I "be too big for it" per se?

Since I have this C40 controller now that I won't be able to use with these current panels and I can't return it what panels can I get to use with it?

Cariboocoot

Re: 48 volts in 12 volts out...where's teh rest of it going????

Off-grid Texan wrote: »

So let's say I want to expand my panel array. I can get more of these panels for $100 a piece! I really can't turn that down. Will the 30 amp charge controller wind up being too small later on and at what point does the 30 become too small? How many panels later will I "be too big for it" per se?

Since I have this C40 controller now that I won't be able to use with these current panels and I can't return it what panels can I get to use with it?

If you are expanding the 30 Amp controller is going to be too small right away as 30 Amps * 12 Volts is 360 Watts and you've got 480 already which when derated will supply maximum current.

In another thread I have suggested you go to 24 Volts. That improves things considerably in the current department, as you'd be able to double the array size on account of the current handling of the Kid controller being the same for all system Voltages. However, given the battery capacity you have you should be thinking of:

Two parallel strings of the 232 Amp hour batteries to give 464 Amp hours @ 24 Volts.
One 60 Amp MPPT controller to provide 46 Amps peak charge current.
1433 Watts of array or more to produce that current.

Your C40 controller will only work properly with panels that have the 'correct' Vmp for the system Voltage. That is 17-18 Vmp for a 12 Volt system, or 35-36 for a 24 Volt system. These panels are becoming difficult to find and more expensive per Watt than the mass-produced 'GT style' panels which usually have a Vmp around 30.

Off-grid Texan

Re: 48 volts in 12 volts out...where's teh rest of it going????

Cariboocoot wrote: »

If you are expanding the 30 Amp controller is going to be too small right away as 30 Amps * 12 Volts is 360 Watts and you've got 480 already which when derated will supply maximum current.

In another thread I have suggested you go to 24 Volts. That improves things considerably in the current department, as you'd be able to double the array size on account of the current handling of the Kid controller being the same for all system Voltages. However, given the battery capacity you have you should be thinking of:

Two parallel strings of the 232 Amp hour batteries to give 464 Amp hours @ 24 Volts.
One 60 Amp MPPT controller to provide 46 Amps peak charge current.
1433 Watts of array or more to produce that current.

Your C40 controller will only work properly with panels that have the 'correct' Vmp for the system Voltage. That is 17-18 Vmp for a 12 Volt system, or 35-36 for a 24 Volt system. These panels are becoming difficult to find and more expensive per Watt than the mass-produced 'GT style' panels which usually have a Vmp around 30.

Thanks a million for all your insight. I really appreciate it.

vtmaps

Re: 48 volts in 12 volts out...where's teh rest of it going????

Off-grid Texan wrote: »

My panels are 240 watts each with an output of 48v and 5'ish amps a piece. They are wired in parallel giving me 48v and about 20-22'ish amps to my charge controller. I know the numbers don't add up in the amp department (5 amps individually but 20 amps when paralleled) but my Fluke voltmeter shows about 20 amps coming in.

Before you buy a new controller or more panels or anything else, you better figure out what's going on here. Do you have a DC clamp ammeter? How are you measuring current? Also, as mentioned, the Vmp is unlikely to be 48 volts.

--vtMaps

Off-grid Texan

Re: 48 volts in 12 volts out...where's teh rest of it going????

vtmaps wrote: »

Before you buy a new controller or more panels or anything else, you better figure out what's going on here. Do you have a DC clamp ammeter? How are you measuring current? Also, as mentioned, the Vmp is unlikely to be 48 volts.

--vtMaps

I'm using my Fluke digital voltmeter touching pos and neg from panels in full sun. DC volts reads 48v +/- and DC amps reads 5'ish. You think the clamp is the best way? I've been wanting a reason to buy one.....

vtmaps

Re: 48 volts in 12 volts out...where's teh rest of it going????

Off-grid Texan wrote: »

I'm using my Fluke digital voltmeter touching pos and neg from panels in full sun. DC volts reads 48v +/- and DC amps reads 5'ish. You think the clamp is the best way? I've been wanting a reason to buy one.....

A shunt is the best way, but not necessarily practical. The clamp meter is good enough. I still don't understand how you are measuring the current with a voltmeter... I'm not suggesting that it can't be done, I'm just curious to know exactly how you are measuring it.

--vtMaps

Cariboocoot

Re: 48 volts in 12 volts out...where's teh rest of it going????

Off-grid Texan wrote: »

I'm using my Fluke digital voltmeter touching pos and neg from panels in full sun. DC volts reads 48v +/- and DC amps reads 5'ish. You think the clamp is the best way? I've been wanting a reason to buy one.....

Reading 48 Volts on the panel output with no load on is the Voc of the panel, and not relevant to the system design. You only see Vmp with the panels loaded. Using the controller you've got the readings wouldn't be accurate even then.

As for the current, you can measure the Isc of one panel with a multimeter by using it as the circuit between the positive and negative leads providing the panel isn't meant to put out more current than the meter can handle (usually 10 Amps). Any other way will not be accurate. The clamp-on meter allows you to read actual current going through a wire in a circuit. In that respect you can see how much current is coming from the panel(s) under the load available, but when that load is a battery the current will not be the maximum the panels are capable of.

Off-grid Texan

Re: 48 volts in 12 volts out...where's teh rest of it going????

Cariboocoot wrote: »

Reading 48 Volts on the panel output with no load on is the Voc of the panel, and not relevant to the system design. You only see Vmp with the panels loaded. Using the controller you've got the readings wouldn't be accurate even then.

As for the current, you can measure the Isc of one panel with a multimeter by using it as the circuit between the positive and negative leads providing the panel isn't meant to put out more current than the meter can handle (usually 10 Amps). Any other way will not be accurate. The clamp-on meter allows you to read actual current going through a wire in a circuit. In that respect you can see how much current is coming from the panel(s) under the load available, but when that load is a battery the current will not be the maximum the panels are capable of.

Alrighty...that clarified a few things. I was testing it wrong...or at least not as acccurately as I could have.

Off-grid Texan

Re: 48 volts in 12 volts out...where's teh rest of it going????

vtmaps wrote: »

A shunt is the best way, but not necessarily practical. The clamp meter is good enough. I still don't understand how you are measuring the current with a voltmeter... I'm not suggesting that it can't be done, I'm just curious to know exactly how you are measuring it.

--vtMaps

I was measuring it the way we did when I installed mobile electronics...just intercept the wire. I have shunts coming from the panel's wires that I can just touch ( (+) and (-) ) to get my readings

Off-grid Texan

Re: 48 volts in 12 volts out...where's teh rest of it going????

Off-grid Texan wrote: »

So let's say I want to expand my panel array. I can get more of these panels for $100 a piece! I really can't turn that down. Will the 30 amp charge controller wind up being too small later on and at what point does the 30 become too small? How many panels later will I "be too big for it" per se?

Since I have this C40 controller now that I won't be able to use with these current panels and I can't return it what panels can I get to use with it?

Since I'm going to expand my array is there any reason not to get the control charger I really want, the Outback 60? Is that one what it states or is it just hype?

Cariboocoot

Re: 48 volts in 12 volts out...where's teh rest of it going????

Off-grid Texan wrote: »

Since I'm going to expand my array is there any reason not to get the control charger I really want, the Outback 60? Is that one what it states or is it just hype?

If you're going to expand, buy the big controller now and get it over with. The MidNite Classic 150 is an 80 Amp controller and will certainly handle 30 Amps now and allow increasing system Voltage. It is a somewhat better controller than the Outback FM60.

I bought an Outback MX60 when I put the first 'big' system in at the cabin. $900 then. Went from 12 Volt to 24 Volt and increased the array size by 50%. Still working, still room to expand. No regrets about buying that big controller!

Off-grid Texan

Re: 48 volts in 12 volts out...where's teh rest of it going????

Cariboocoot wrote: »

If you're going to expand, buy the big controller now and get it over with. The MidNite Classic 150 is an 80 Amp controller and will certainly handle 30 Amps now and allow increasing system Voltage. It is a somewhat better controller than the Outback FM60.

I bought an Outback MX60 when I put the first 'big' system in at the cabin. $900 then. Went from 12 Volt to 24 Volt and increased the array size by 50%. Still working, still room to expand. No regrets about buying that big controller!

Excellent info! Thanks again good Sir!