solar battery problem: will not charge from solar when in series (24v) they do in parallel (12v)

I live in a remote part of Tanzania with no mains electricity. We have had solar power for some time, but on purchasing a new inverter, battery and extra solar panels have run into problems. The problem can be simply stated. We have two N200 lead acid batteries both yielding 12-13V each. Connected in series we get 25v from the system.

The inverter (Shiv Solar Comercial UPS 2000-24V) requires that the batteries be connected in series. If they are connected in parallel the inverter quickly triggers a ‘low battery warning’.

But the batteries will not charge when connected in series. Each will charge on its own. So there does not appear to be a problem with any of the connections. Moreover both will charge together when connected in parallel. Nor does it make any difference which way around we connect the batteries in series.

When I say that they do not charge I mean that the charging sign on the controller indicates that the batteries are not charging. Also the Amp level reads ‘0’ for both the solar panels and the batteries. The volts show a positive reading (batteries on 25, solar panels vary according to the sunlight).

We know that single batteries charge on their own because the charging sign on the charge controller indicates that they are and the ampage is positive both for the panels and the battery (varying according to the sunlight).

What would cause this problem?

The only thing I can think of may be that the solar charge controller (ViewStar series 4048) has limits set in it, that prevent charging when the batteries are connected in series. But its internal limits seem to be fine for the batteries needed. When we connect them in parallel it detects a 12V system and sets parameters accordingly. When we connect them in series it detects a 24V system and doubles the parameters

I'm guessing you didn't rewire your solar array for 24V (nominal).

Your charge controller will support 24V battery banks, but it needs to have the panels wired to work with the higher voltage.  You can't charge a 24V battery bank from a 12V PV array.

I.e. if you only have 1 panel, then you'll need to get a second panel that matches your first and wire them in series.  If you already have 2, then wire them in series instead of parallel.
If you have more than 2 (4 or 8, etc.) wire them in series/parallel.  I.e. wire them in groups of two in series, and then wire all the groups in parallel.  If you have an odd number of panels, then either leave one out, or get another one that matches.  Ideally you want to use all panels that are the same brand and type.  If you need another panel and can't get the exact same type, then make sure the new one has similar specs.

Peter, thanks so much for a super quick reply that could indeed solve the problem. We have 6 panels. So I'm guessing we need to put them in three pairs - each pair in series and then the three pairs in parallel. Please could you confirm / corrent?
Would you mind if I sent you a diagram of what we end up doing? thanks again.

Yes that's correct.  

I'd be happy to review your diagrams.

Basically what you want is something like this:

Thanks Peter, you are quicker at drawing than I am, that looks like what we will attempt. I've just been up on the roof to check how things are wired. We currently have 2 sets of 3 panels. So 3 panels in series. And then the two sets of three meeting in the charge controller. Each panel is 100 watts. We originally had 4 panels (in two sets of two) which sufficed for the 12v system. So I'm guessing that in not going 3*2 that was our mistake. Does this sound reasonable?

Apologies, please ignore my last while I double check the wiring, I may have got that wrong.

Hello Dan. Is that Viewstsr 404 a older Renogy charge controller? I don't see it on their website. I hope your charge controller didn't go bad.  They sometimes go bad when a system is worked on. Some charge controllers only like to be connected to the battery before the solar. I always turn the battery on first but gave forgotten a couple times.
Some charge controllers have auto detect for the battery voltage. I was trying to look yours up. Some have dip switches inside to adjust voltage settings.
If you do indeed have three 12 volt panels in series then you should not need to change them for a 24 volt system. 2 in series is the minimum for a 24 volt system.
I'm assuming you upgraded to a 24 volt inverter and battery from a 12 volt inverter and battery. If the 404 charge controller will auto adjust to 24 volts then it should work unless something else is incorrect. Such as a dip switch inside the charge controller needs to be changed from 12 to 24.  
If that doesn't fix it check the input voltage to the charge controller and let us know. Check fuses or breakers.

Agreed do you have a link to the charger's manual? It's obviously in the controller. I would also look into how those strings of 3 are wired. We are assuming they are wired for 36 volts going into an mppt charger but I've seen a lot of older systems with smaller panels that had the 12 volt panels wired in parallel into a pwm charger. Then they upgraded to an mppt and never re did the strings. I would take a volt meter to each string where it enters the charge controller and get more detail on the controller.
Cheers,  David Baillie

I am not a super expert on solar systems, but I consider myself to be beyond novice at batteries in general- especially lead acid sealed and unsealed types.  (Glass mat, standard car battery, etc.)

I run a program here in North Dakota where I give away refurbished Uninterruptible Power Supplies to police, fire, medical and county\city governments.  I take old emergency lighting, alarm batteries, etc that are being tossed by companies here about along with UPSs that "no longer work."  I take batteries from elevator companies, alarm companies, that sort of thing.  Many can be salvaged to at least 80%, most 90% or better of original capacity, simply by popping their supposed "sealed" status and adding in distilled water to each cell.  Then doing a light charge, topping off again and repeat until you are sure it's ready for a full charge.  It usually takes two light charges to make them "settle in" and absorb enough water back into the mat to return to normal capacity.  

My point to that is, that I have learned a few tricks about batteries in series or parallel.  And it sounds like to me that I know what's happening here.  Or at least might suggest a way to determine what might be happening.

So anytime you have more than one battery in a system, an odd thing can happen.  Let's say you have two old batteries wired up like I do.  You take the first one and let's say it's at 95% of original capacity.  Certainly still useable, nearly brand new.  And you place that in partnership with a battery that's running at 80% efficiency.  In a "dumb" system, the machine does not care.  But in a smart system, it can cause trouble.  Here's how.

The charge controller is always busy monitoring these batteries, trying to keep them at peak.  That is of course what you want.  But with unequal batteries, the machine can get confused.  

Now I am not an expert, but I know from a practical sense this happens and I have seen it with my own eyes.  A charger works by measuring resistance to current in the charge circuit.  When it senses the system is filling, it backs off the amps and gently tops off.  Well you can then see how having more than one battery in a system can confuse the charge controller.  The battery at 98% efficiency is screaming, "Hey I am starving here!"  The other is screaming, "I am going to burst!" because it's at 80% efficiency and will hold far less of a charge.  Put those in series and you can confuse the heck out of a battery charge controller.  Especially since the weak battery will not pass current through like the strong one will.  The charge controller has no way to adapt and so throws an alarm.  It's trying to tell you, "One of these things is not like the other, one of these things is dead..."  (Sorry, a spoof on a popular children's show here in the states.)

So here's how to check if that is the issue.  Sure, you could measure specific gravity, etc, but the simplest, easy way is to charge each battery separately.  Once the system says battery A is fully charged, let it settle down to base voltage.  Batteries are "hot" after charging and will lie to you about their voltage state.  Give them a while to settle, like say, two hours.  Charge battery B while you wait.  Measure the voltage in battery A two hours after charging.  Then measure the voltage in battery B two hours after charging.  If there's a significant difference, you found your problem.

One of these batteries is likely not what it use to be and the charge controller is trying to tell you that.  It's smart enough to know there's a problem.

Again, I am no expert, but my lack of knowledge means I notice the little things.  Instead of thinking this is a problem with the system, my spidy senses tell me you have a bad battery.  One of them is going south and the controller is saying so.  Therefore it does not want to ruin the other, still good battery.

You can likely still use the "bad" one.  Just make sure it's in a system with other "geriatric" batteries.  If it's a sealed lead acid, it might just need some distilled water.  I can write up how I salvage geriatric SLAs and send it to you if you like.      

Do let us know if this bit of advice proves true, won't you?

JR

Folks,

Thanks all for these suggestions and comments. It was Peter's suggestion that nailed it. The 6 panels had been connected in parallel. I reconnected them in series (3 lots of 2) as suggested, and now the batteries are charging. @Peter - thanks much!

We may still have problems with the controller - and we may also have batteries of unequal strength (@Jeffrey thanks for that tip). One is new and one not - but both were fully charged at the local charging station before installation. We will keep an eye on them. At the moment I'm just enjoying being able to work the fridge, computer and water pump without the batteries dying.

One more question if I may: Our bulbs are 12v dc and several of them, of course, melted when the 24v system was connected. (I do hope you find this as amusing as my family did). We have now wired the bulbs to *one* of the batteries which is connected in series. Will this yield a 12v supply, or will there still be 24 v coming off the one battery.

thanks again,

Dan

It's usually a bad idea to mix old batteries with new ones.  Old batteries require more current to fully charge and all this extra current will ruin the new battery.  Often the new battery will fail before the old one.

If the new battery is really new, go buy another new one, if you can.  Otherwise just realize that your battery bank won't last very long and start budgeting to replace both batteries.

Glad I could help.

Dan,

I am a bit worried about your question on wiring up to just one battery and wondering if that's 12 Volts or not.

Do you have a volt meter?  If not, there are some pretty cheap ones out there that are excellent with DC systems like this.  (I would not trust them with mains though.)  For $25 US, you can get an accurate volt meter.  Then you can measure the voltage coming off your single battery and avoid "melting bulbs."  (Not really sure how it is that a bulb can melt, lol.  Do you have photos?  You seem to be describing a very strange phenomenon....)

Measure the voltage on the leads and you will discover the answer to your question.

If you don't have even a cheapo "multi-tester" type volt meter, you should truly get one!  You will save yourself so much expense and dark nights without lights...  The multitester will pay for itself in replacing equipment right away and also in peace of mind.  

JR

Peter, thanks again, we will look for a new one. I'm hoping given that the older battery is only 3 months old that things will not be too bad. Do you know if there is a window of acceptable age difference for old and new batteries.

Also do you know the answer to the question I posed at the end of my previous post?

Dan

What type of battery?  If it's a good quality deep cycle battery, then 3 mo is acceptable.  If it's something like a "Marine" battery, then 3 months is probably 25-30% of it's expected lifespan.

However, given that you are using 12V batteries, I'm guessing it's not really a deep cycle battery.

You can wire the 12V appliances to just 1 battery and you will get 12V, but that battery will wear out faster.  I'd recommend either getting a 24V to 12V DC-DC converter, or switching to lights, etc. that can handle 24V.  There are some LED bulbs out that work on both 12V and 24V.

You can either purchase 24 volt led bulbs to replace the 12 volt ones or a voltage converter like this one
https://m.ebay.com/itm/Waterproof-DC-DC-Converter-Voltage-Regulator-24V-to-12V-Step-Down-20A-240W-new/192121585753?hash=item2cbb56c059:g:7ucAAOSwhlZYvQOA
And run it from your full voltage battery bank to the 12 volt loads. That is what we recommend to people who switch to 24 volts. Tapping off one battery to get 12 volts is possible but will lead to premature death of that battery.
Glad you solved your problem...
Cheers, David

FOlks,

thanks again for this helpful advice; I will source a voltage converter soon.

with best wishes

Dan