Hot batteries?

cptdondo

I have a pair of Trojan T145s. They are charged by a couple of solar panels with a Sunsaver Duo PWM controller, with a total of 240W of output.

The batteries have a fairly constant drain of about 1A on them, 24/7. The solar panels are more than capable making up the 24Ah the drain takes out.

I just started the electric fridge, which uses about 5A. The battery voltage dropped to 11.89 almost immediately (after about 15 minutes of use) and is now holding steady.

The batteries are new (4 month old) and have been checked and water replenished as needed; they don't need much so everything seems to be OK - except for the immediate voltage drop.

The battery temp is 111 deg F.

Could the high battery temp account for the voltage drop?

solar_dave

Re: Hot batteries?

cptdondo wrote: »

I have a pair of Trojan T145s. They are charged by a couple of solar panels with a Sunsaver Duo PWM controller, with a total of 240W of output.

The batteries have a fairly constant drain of about 1A on them, 24/7. The solar panels are more than capable making up the 24Ah the drain takes out.

I just started the electric fridge, which uses about 5A. The battery voltage dropped to 11.89 almost immediately (after about 15 minutes of use) and is now holding steady.

The batteries are new (4 month old) and have been checked and water replenished as needed; they don't need much so everything seems to be OK - except for the immediate voltage drop.

The battery temp is 111 deg F.

Could the high battery temp account for the voltage drop?

How about wiring sizes? Under size with an increase might be an issue.

cptdondo

Re: Hot batteries?

I don't think so.... The voltage is being reported by the SunSaver and also by the buck-boost supply driving the 1A load, both with plenty big wiring for the load they're carrying.

The fridge is wired with a good sized wire (I can't recall offhand but at a guess it's 14ga). The batteries themselves are connected with 2ga welding wire with crimped on copper connectors.

I've never had issues with current capacity before.

But.... There is one possibility - there is a 30A thermal breaker in line... And a latching solenoid. I'll have to check these if it's not the batteries themselves.

cptdondo

Re: Hot batteries?

Interesting... I checked this morning. Voltage under load down to 11.53. EEK! So I shut everything off and took the dog for a walk. When I came back, the batteries had recovered to 12.37, which, according to the Trojan voltage chart, is an SOC of 70%. Doing the math: 260 AH * 30% = 78 amps drawdown, which is about right - 11 hours @ 5A for the fridge + 11 hours at 1A totals about 65 amps. Maybe the batteries just drop that low under use, and maybe it's more pronounced with higher battery temps.

Cariboocoot

Re: Hot batteries?

Let's see ... 260 Amp hour 12 Volt battery bank, 240 Watt array producing about 13 Amps of current making the peak charge rate a mere 5% or half of what Trojan recommends for the batteries ...

Have you tried checking the specific gravity of the batteries to see if they are dead?

cptdondo

Re: Hot batteries?

The panels are Kyocera KD135GX 135 Watt. I have 2 of them, so about 270W nominal. But the SunSaver Duo tells me that they peak at 29A in bright sunlight, so I think they're underrated. I'll check the SG. I occasionally charge them from the car alternator too. Maybe I'll do that more often as part of regular maintenance when I check the water level.

cptdondo

Re: Hot batteries?

I can also charge these batteries from a 3 stage 45A charger. I've just been relying on the solar panels. Maybe I need to use the charger weekly to make sure the batteries are fully charged.

icarus

Re: Hot batteries?

Is that fridge 5 amps at 12 vdc or 5 amps t 120 vac? Makes a big difference.

Icarus

cptdondo

Re: Hot batteries?

icarus wrote: »

Is that fridge 5 amps at 12 vdc or 5 amps t 120 vac? Makes a big difference.

Icarus

5A DC. It's a bit hard to estimate as the fridge has an intelligent controller that attempts to minimize power usage when on batteries by varying the compressor speed and runtime... But as it was 105 yesterday, and the fridge had to cool that off, I figure it ran with the compressor on full all night.

I plugged the 45A charger in and it immediately took the batteries to 14.1V, so we'll see if there's any damage to them from the lower charge levels of the solar panels.

Cariboocoot

Re: Hot batteries?

cptdondo wrote: »

The panels are Kyocera KD135GX 135 Watt. I have 2 of them, so about 270W nominal. But the SunSaver Duo tells me that they peak at 29A in bright sunlight, so I think they're underrated. I'll check the SG. I occasionally charge them from the car alternator too. Maybe I'll do that more often as part of regular maintenance when I check the water level.

The KD 135 has an Imp of 7.7, so 29 Amps from two of them even in bright sun isn't possible. Your SunSaver Duo (This one? http://www.solar-electric.com/modubachco25.html ) seems to be inaccurate. I can't believe the panels are putting out double their rated current, or that you miscounted panels and left two out.

Your car alternator is an expensive way of Bulk charging, and won't do a complete charge. You probably realize that.

For keeping track of the refrigerator's total use you need some kind of battery monitor. Total daily power consumption on that 'frige could be 24 Amp hours for the 1 Amp constant load plus 4 Amp hours * 24 hours * duty cycle (1/3?). Possibly 56 Amp hours? Now here's a curious thing: take 14 Amps from the panels, multiply by 4 hours equivalent good sun, and you get ... uh, 56 Amp hours. If the 'frige runs longer (1/2 duty cycle) and/or the panels produce less you get deficit charging.

cptdondo

Re: Hot batteries?

Cariboocoot wrote: »

For keeping track of the refrigerator's total use you need some kind of battery monitor. Total daily power consumption on that 'frige could be 24 Amp hours for the 1 Amp constant load plus 4 Amp hours * 24 hours * duty cycle (1/3?). Possibly 56 Amp hours? Now here's a curious thing: take 14 Amps from the panels, multiply by 4 hours equivalent good sun, and you get ... uh, 56 Amp hours. If the 'frige runs longer (1/2 duty cycle) and/or the panels produce less you get deficit charging.

Hehe. Not so curious; the system was sized to handle the refrigerator load. On a hot day, the fridge uses about 50Ah, so the system was sized to replace that. On a not-so-sunny day, the fridge uses less; on a cool cloudy day the fridge uses about 17Ah. There's big slug of power when you initially turn on the fridge as it has to cool down the enclosure, but once at temp it's pretty frugal.

I cooked the last set of batteries by using the alternator, so now I'm trying to err on the other side.

I'm working on a battery monitor. I don't like the solutions out there so I'm rolling my own. (Long story, but there's no battery monitor that's suitable for small RV use and that monitors multiple banks.)

Cariboocoot

Re: Hot batteries?

cptdondo wrote: »

I'm working on a battery monitor. I don't like the solutions out there so I'm rolling my own. (Long story, but there's no battery monitor that's suitable for small RV use and that monitors multiple banks.)

Well the Pentametric can monitor three shunts IIRC. It can do two battery banks with common negatives (and same Voltage). A bit pricey. http://www.solar-electric.com/pe3chbamosy.html

rgk1

Re: Hot batteries?

The SunSaver Duo looks like it has temperature compensation. You said the batter temp is 111F. Are the batteries in an even hotter environment allowing them to get that hot? If so, with temp compensation, it doesn't seem that far fetched. But I'm not a math guy either.

Cariboocoot

Re: Hot batteries?

Another straightforward test: measure the Voltage at the battery with a DMM. Measure it at the inverter. Should be the same. Then turn on a load. Voltages should still be the same at both locations, +/- a small amount. If the Voltage at the inverter goes down under load but not at the battery, the wiring is at fault. if both go down either the batteries are no good or the load is a lot bigger than it should be (short somewhere perhaps).

cptdondo

Re: Hot batteries?

Cariboocoot wrote: »

Another straightforward test: measure the Voltage at the battery with a DMM. Measure it at the inverter. Should be the same. Then turn on a load. Voltages should still be the same at both locations, +/- a small amount. If the Voltage at the inverter goes down under load but not at the battery, the wiring is at fault. if both go down either the batteries are no good or the load is a lot bigger than it should be (short somewhere perhaps).

I'm starting to suspect something like that. I've had the engine voltage drop for no apparent reason recently from a rock-steady 14.4 to a fluctuating 13.9 - 14.1, along with fast blinkers when the engine RPM drops.

All this seems to indicate a bad ground somewhere; possibly multiple bad grounds.... The fun never stops....

cptdondo

Re: Hot batteries?

Spent some time with a DMM. It would help to be contortionist....

But it looks like one of the cells in one of the batteries is bad.

I'm getting 6.24 V across one battery, and 5.65 across the other. These are in series, and the cells are filled identically.

Maybe a trip to the battery place is in order.

Cariboocoot

Re: Hot batteries?

Fully charged you should have 6.375 Volts per battery. One is a little low, the other is a lot low. Almost one whole shorted cell low. If you have the means to do so, try an equalization cycle and see if there is any improvement. If there is, try again. If there's not or you can't get it up to the same Voltage ... it's new battery time.

Vic

Re: Hot batteries?

... Wonder if one battery is a lot hotter than the other (?).

At 111 F those are/were some HOT batteries!

The banks here were about 85 F the other day, and that was concerning to me.

It is true that we can only do what we can co. Good Luck, Vic

cptdondo

Re: Hot batteries?

Vic wrote: »

... Wonder if one battery is a lot hotter than the other (?).

At 111 F those are/were some HOT batteries!

Yeah... The ambient temps were about 104 deg F on the pavement. The batteries are in a compartment with limited ventilation, so 111 deg. F is not out of the question.

The plot thickens, though - took the batteries to the local Trojan dealer. Both tested fine, including voltage. No idea why one was lower than the other when I checked. It's possible that I had some minor corrosion on one of the battery clamps that was causing the problems. Anyway, both check out fine, but he did replace the one that I tested low.

Charging from the 45A charger as we speak.

westbranch

Re: Hot batteries?

did he give you the SG readings? they could be very important for follow-up.