Sudden failure to charge

jvglynnjr · February 2011

Help! My PV system that has been working fine for over four years has suddenly stopped charging.

I have four 75-watt panels connected via a Tristar T-45 charge controller to four Trojan 6-volt batteries wired in series (24-volt system).

Currently the battery voltage reads 23.6 V. Yesterday I suspected that the charge controller was at fault and disconnected it. The panels showed (and still show) an open-circuit voltage of >40 V when the sun is shining. When I connected the panels directly to the battery, it showed current flow of 3-4 A briefly the first day (it was a partly cloudy day) but now, on a sunny day, I am getting 0.00 A.

I can't find any disconnections or discontinuities. I thought maybe my display meter (which operates off of a shunt) could be malfunctioning, so I ran the PV input directly through a 10 A ammeter, still no current.

I have two friends with extensive PV experience scratching their heads over this one, and they say it just doesn't make sense. They also tell me that it doesn't have the symptoms of battery failure.

Any clues? What went wrong? What to check next?

BB. · February 2011

Re: Sudden failure to charge

Use a Volt meter and check across each major connection (voltage drop)... Good connections should have less than 0.1 volt drop, bad connections will be >>0.1 volt drop.

Tell us what the voltage is on the PV Input for the charge controller (full sun) and what the voltage is on the Battery Output (Controller). And what is the voltage at the battery bank (1X.XX accuracy).

If you have a Sears nearby, they sell a 400 Amp DC Clamp meter for ~$60.00+tax or so...

-Bill

mike95490 · February 2011

Re: Sudden failure to charge

And , quickly get some sort of charger on your batteries, and charge them up before they sulfate and die.

icarus · February 2011

Re: Sudden failure to charge

Test the open circuit voltage of each panel.

How are your panels wired, for 24 volts, series, parallel or series/parallel?

Tony

n3qik · February 2011

Re: Sudden failure to charge

I would, using your hand held meter, test the short circuit current of EACH panel.

jvglynnjr · February 2011

Re: Sudden failure to charge

BB. wrote: »

Use a Volt meter and check across each major connection (voltage drop)... Good connections should have less than 0.1 volt drop, bad connections will be >>0.1 volt drop.

Tell us what the voltage is on the PV Input for the charge controller (full sun) and what the voltage is on the Battery Output (Controller). And what is the voltage at the battery bank (1X.XX accuracy).

If you have a Sears nearby, they sell a 400 Amp DC Clamp meter for ~$60.00+tax or so...

-Bill

Thanks for your reply.

Well, I checked all of the connections, and they all had >100 mV drop, so I took them all apart and cleaned them, and now they are all <0.1 mV. Still getting 0.0 A on my readout, but now when I connect my ammeter in series with the PV output, I get 20 mA. (also, my display has the "charging" indicator lit while showing 0.0 A, so I'm assuming the batteries are charging at a measly 20 mA)

I didn't have time to get to town to buy an amp clamp, but I guess this is some progress.

I can only read voltages to the nearest 0.1 V in that range, so all I can say is that all the ones you asked about are 23.5 V. When I connect the charge controller, it still shows the red LED which is supposed to indicate "battery discharging."

A curious observation: when I had the battery connections all apart to clean them, I checked the voltage on each battery, and found they were all just 4.5 V!! Yet when I put them all together in series I get 23.5V. How is that possible? Where did the extra 5.5 V come from?

Cariboocoot · February 2011

Re: Sudden failure to charge

4.5 Volts? If your meter can be trusted those batteries are shot. At that point they probably won't draw any current. If I'm reading your specs right, you have only 300 Watts of panel in total. That is not enough to charge a 24 Volt system with 225 Amp hours of battery:

300 * 77% = 231 "usable" Watts / 28.4 charging Volts = 8 Amps of current.

There's your problem.

BB. · February 2011

Re: Sudden failure to charge

One thing to watch out for--The "small" voltage drop across connections is created by flowing current... Basically Voltage=Current*Resistance... If Current~0.0 amps, then there will be ~0.0 volt drop. So--it is unclear to me, if your cleaning helped or not (certainly did not hurt).

Do you have grid power and a battery charger available? If so, attach the battery charger to the place where the solar charger connects and start charging the batteries (you don't want them to sit for long at low voltage/state of charge--Below ~75% state of charge, the cells will begin to sulfate).

If this is off grid... You can try connecting the solar array directly to your battery bank and get some sort of charge going. (be sure polarity is correct--hook the panels up reverse polarity--and they will be instant environmental art).

If you get no increase in battery voltage/measured current, then there is still something wrong.

-Bill

jvglynnjr · February 2011

Re: Sudden failure to charge

BB. wrote: »

One thing to watch out for--The "small" voltage drop across connections is created by flowing current... Basically Voltage=Current*Resistance... If Current~0.0 amps, then there will be ~0.0 volt drop. So--it is unclear to me, if your cleaning helped or not (certainly did not hurt).

Do you have grid power and a battery charger available? If so, attach the battery charger to the place where the solar charger connects and start charging the batteries (you don't want them to sit for long at low voltage/state of charge--Below ~75% state of charge, the cells will begin to sulfate).

If this is off grid... You can try connecting the solar array directly to your battery bank and get some sort of charge going. (be sure polarity is correct--hook the panels up reverse polarity--and they will be instant environmental art).

If you get no increase in battery voltage/measured current, then there is still something wrong.

-Bill

I've already direct connected them and am only getting 20 mA.

I've got grid power but I've only got a 12-volt battery charger. Can I charge them two at a time with it?

jvglynnjr · February 2011

Re: Sudden failure to charge

Cariboocoot wrote: »

4.5 Volts? If your meter can be trusted those batteries are shot. At that point they probably won't draw any current. If I'm reading your specs right, you have only 300 Watts of panel in total. That is not enough to charge a 24 Volt system with 225 Amp hours of battery:

300 * 77% = 231 "usable" Watts / 28.4 charging Volts = 8 Amps of current.

There's your problem.

I'm not sure I follow what you're saying. It sounds like you're saying the design specs are inadequate, yet this system has been running just fine for over four years. Yes, it's 300 W of panels.

Cariboocoot · February 2011

Re: Sudden failure to charge

jvglynnjr wrote: »

I've already direct connected them and am only getting 20 mA.

I've got grid power but I've only got a 12-volt battery charger. Can I charge them two at a time with it?

Yes.
Don't be surprised if the AC charger also doesn't show much current flow.

BB. · February 2011

Re: Sudden failure to charge

It would be very helpful if you can measure the resting voltage of each battery, and the whole string +/- 24 volt terminals... And again do it when everything is charging (perhaps with solar--which does not sound like it is working) and with an external charger (AC battery charger), etc...

If you have an open cell somewhere in the battery bank, you will see low voltage on three of the batteries and rediculusly high voltage on the forth (if 4x 6 volt batteries in series).

Basically, if everything is working correctly in the battery bank, all battery voltages should be similar between all batteries. If you find something "off", especially when under charge or under load, then you have found something that need further investigation.

If all batteries are still roughly equal in voltage (within 0.1-0.2 volts) but there is little current flow (very high voltage when charging but no current, or very low voltage when discharging and not much current) then you may have severely sulfated batteries--But that does not sound right--The batteries will usually gradually fail.

Although, I have seen older sets of batteries that were taken dead once--work for a few days or weeks, then just fail to supply any current (such as a car--take battery dead, recharge, drive for a week or two, then all of a sudden, the starter refuses to crank).

Make a chart of your battery bank and measure the voltage across each bank and on the end of each string--Write down the voltages and see if you can find a pattern (do this when charging, discharging, and resting).

It is possible that the charge controller has failed... But as n3qik says, measure the Voc (voltage open circuit) of each panel/connection and the Isc (short circuit current) of panel (watch max current limit of meter) to verify that the panels are OK.

-Bill

Cariboocoot · February 2011

Re: Sudden failure to charge

jvglynnjr wrote: »

I'm not sure I follow what you're saying. It sounds like you're saying the design specs are inadequate, yet this system has been running just fine for over four years. Yes, it's 300 W of panels.

That's right: under spec'd.
If these are Trojan T105's then they are 225 Amp hours. Trojan suggests a charge current of 10% of that. So you have calculations that look something like this:

22.5 Amps @ 28.4 Volts = 639 Watts, minus efficiency derating = 830 Watt array.

I have almost the same size system with 700 Watts of panels. Mine run closer to 80-82% efficiency due to high altitude. It is barely adequate for proper charging.

The thing is "has been running fine for over four years" is about what to expect for such circumstances. The plates sulphate slowly, capacity goes down, apparently they're being charged, then one day you no longer have enough Amp hours to run anything. Catastrophic internal failure, very high resistance, no current flow in to batteries even though the charge system is 100% active. Those batteries should have lasted twice that time.

A six Volt battery at 5.25 Volts is dead as a doornail. At 4.5 Volts it's scrap metal.

Try charging two in series as a "12 Volt" battery off your automotive charger (10 Amps at least). Don't be surprised if it doesn't work. You may want to put a load on the battery when you start charging too; it "fools" the (automatic) charger into kicking out higher current to begin with. Take the load off once you see the Ammeter go up. Even if it appears to charge the batteries, chances are the charge won't hold over night. If you've got a hydrometer, check the specific gravity after charging and resting. It probably won't be over 1.200.

jvglynnjr · February 2011

Re: Sudden failure to charge

Well, thanks for your insights, everyone. I've had two of the batteries on a charger for a couple of hours now. The voltage is at 11.7 V. I'm going to try the other two on a trickle charge overnight.

niel · February 2011

Re: Sudden failure to charge

at 11.7v it's going to need a lot more than a trickle charge.

just from the overview in rereading the thread, i've come to question the reliability of the meter you are using for if it's reading wrong there could be trouble in trying to force the battery voltage higher by that meter. if it isn't the meter then possibly some human error in measurement. what really changed here, was it your system or the meter?
this was just a possible avenue of thought you should consider as this is serious for damage to the batteries may occur either way as one shows depleted and the other possibility of erroneous low voltage readings could cause a severe overcharge.

n3qik · February 2011

Re: Sudden failure to charge

niel wrote: »

just from the overview in rereading the thread, i've come to question the reliability of the meter you are using for if it's reading wrong there could be trouble in trying to force the battery voltage higher by that meter.

Let's check this meter. Pop the hood on your car. What is the voltage of that car battery?

jvglynnjr · February 2011

Re: Sudden failure to charge

niel wrote: »

at 11.7v it's going to need a lot more than a trickle charge.

just from the overview in rereading the thread, i've come to question the reliability of the meter you are using for if it's reading wrong there could be trouble in trying to force the battery voltage higher by that meter. if it isn't the meter then possibly some human error in measurement. what really changed here, was it your system or the meter?
this was just a possible avenue of thought you should consider as this is serious for damage to the batteries may occur either way as one shows depleted and the other possibility of erroneous low voltage readings could cause a severe overcharge.

I had the automatic charger set for 10 A overnight, but it doesn't look like it did anything. When I ran it through my ammeter it showed 0 A. I've reconnected the batteries, and the overall voltage is still 23.5 V. Reading across the four separate batteries while they're in series gives: 5.90 V, 5.89 V, 5.87 V, 5.91 V. Panels still show an open circuit of >40 V, but still not charging.

I'm going to try to get the batteries tested this week.

jvglynnjr · February 2011

Re: Sudden failure to charge

n3qik wrote: »

Let's check this meter. Pop the hood on your car. What is the voltage of that car battery?

I don't think there's anything wrong with my DMM. It shows 12.54 V on the car battery.

jvglynnjr · February 2011

Re: Sudden failure to charge [solved]

Well, it turned out there was a break in the wire between the solar
panels and the building! If I had checked continuity like I was going
to, first thing, when this trouble started, it would have been a lot
less fuss. I learned something, though: you can still have a voltage
even if the wire's no good! It read open even in the 2 M-ohm range.

I got the batteries charged up with a 35 A charger, and now everything is back to normal.

Thanks, everyone, for your input.

-j

n3qik · February 2011

Re: Sudden failure to charge

That is good to know. Now the million dollar question.

Why did the wire break???
And
Can the other one be damaged also?

jvglynnjr · February 2011

Re: Sudden failure to charge

n3qik wrote: »

That is good to know. Now the million dollar question.

Why did the wire break???
And
Can the other one be damaged also?

The guy who installed the panels used salvaged Romex to run from the panels to the building. Unbeknown to me, he "repaired" some damage to the insulation with some electrical tape, and left this wonder out in the weather, where I guess it had some leakage current for years before it finally corroded enough to raise the resistance in the wire high enough to block the current.

It's only about 100 ft of wire, so I'm going to get an outdoor rated piece to replace it. Meanwhile, I have it hobbled together with some butt connectors and shrink tubing.

KeithWHare · February 2011

Re: Sudden failure to charge

jvglynnjr wrote: »

The guy who installed the panels used salvaged Romex to run from the panels to the building. Unbeknown to me, he "repaired" some damage to the insulation with some electrical tape, and left this wonder out in the weather, where I guess it had some leakage current for years before it finally corroded enough to raise the resistance in the wire high enough to block the current.

It's only about 100 ft of wire, so I'm going to get an outdoor rated piece to replace it. Meanwhile, I have it hobbled together with some butt connectors and shrink tubing.

100 feet on romex? What gauge is the wire? You may want to take a look at a voltage drop calculator and consider putting in larger wire while you are replacing it.

Keith

jvglynnjr · February 2011

Re: Sudden failure to charge

KeithWHare wrote: »

100 feet on romex? What gauge is the wire? You may want to take a look at a voltage drop calculator and consider putting in larger wire while you are replacing it.

Keith

It was 12 gauge. I thought I would probably go to 10 gauge, but I haven't done any calculations.

techntrek · February 2011

Re: Sudden failure to charge

Going with some of your numbers from your first post, I plugged in 48 volts from the PV, 6 amps, 10 gauge wire, 100 feet one-way and get a 3.1% voltage drop. If you can afford it 8 gauge wire will only give you a 1.9% drop.

niel · February 2011

Re: Sudden failure to charge

i have another concern here for back in your post #17 you put a 10a charger to it and didn't yield any results. is your charger faulty for the wire problem you found would not have affected the charger unless you are using the full length of the wire to send that charge to the batteries with?

Sudden failure to charge

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