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Old 09-12-2020, 08:49 PM   #1
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Coach Battery Issue

Hi Guys!

I have 4 Interstate GC2-XHD-UTL batteries for the coach. These are 6V batteries so they should be 24V or so when full?

Up to this point, they worked fine but are typically never used except for short periods.

Yesterday I had to get both windshields replaced and the unit was left from 8AM until about 10AM the following day. To keep the fridge running I turned the inverter on.

When I came in the next day the fridge was beeping and saying NO AC. I figured the batteries had drained and so I checked the food in freezer to see if it was still frozen and it was. Pop was cold etc so I figured they ran out not long ago.

So..now it's plugged into 50 amps and the inverter fan has been running for hours. The panel seems to indicate it's stuck on bulk charging and that the batteries are at ~30%.

I went out and pulled the caps off all the cells. All of them are boiling. I then checked the voltage and it's 14.6v

I'm guessing the batteries are shot. I would have thought the inverter would have given up charging after being on bulk for so long.

What do you guys think? Batteries?
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Old 09-12-2020, 09:05 PM   #2
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NO.


Your 4 6VDC batteries are wires in series/parallel.


Basically two 12 VDC batteries.


Charged, around 13.2 on charger. Around 12.7 fully charged charger off.
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Old 09-12-2020, 09:06 PM   #3
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Oh-Oh. Wouldn't that mean that the charging side of the inverter is shot?
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Old 09-12-2020, 09:19 PM   #4
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Originally Posted by BobJones View Post
Oh-Oh. Wouldn't that mean that the charging side of the inverter is shot?

The charger is fine, you can set the voltage at 14.4 if you feel it's too high. It takes at least 4 hours to get to float from a normal 50% discharge so you are fine.
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Old 09-12-2020, 09:26 PM   #5
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Originally Posted by wolfe10 View Post
NO.
Charged, around 13.2 on charger. Around 12.7 fully charged charger off.
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The charger is fine, you can set the voltage at 14.4 if you feel it's too high. It takes at least 4 hours to get to float from a normal 50% discharge so you are fine.
OK, but...if fully charged is in the neighborhood of 13.2, and they are at 13.65 (at last check), the panel still shows bulk charging and the percentage at 30%.

Shouldn't it be reading much higher since the batteries appear to be nearly fully charged? Or switched over to float charging?
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Old 09-12-2020, 09:45 PM   #6
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I'm guessing here, so some one can tell me if I'm wrong. But since you fully drained the batteries instead of just 50% your charge controller may need to be reset. One of the ones I was looking at said to get an accurate battery level reading i needed to fully charge the batteries then set the battery meter to 100%. I'm no battery expert but that's what I read from a manual of another controller. Hope it helps.
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Old 09-12-2020, 10:18 PM   #7
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How old are your Interstate GC2 batteries?
Like NVS says, you are supposed to limit the discharge to 50%. Your inverter should have a low voltage battery cutout to prevent more than 50% discharge. Do you know what this was set to?

If you fully discharge them, it can take a couple of days to fully recharge and if they are older, you can damage them.

Also, you cannot properly measure the battery voltage when they are charging. You are measuring the voltage from the inverter charger. Voltage is like pressure in a water hose and to force power back into the battery takes a higher pressure than the internal pressure in the battery.
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Old 09-12-2020, 11:41 PM   #8
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Hi Vito!

I don't know their exact age but I would guess 7 years might be accurate. They have always had power to them (for charging) and were more/less never used. It would be accurate to say they sat idle, fully charged and maintained.

With respect to low voltage battery cut out, that is set by a jumper inside the inverter. I will look tomorrow to see what it is set at but it can be either 11.8v or run until dead.

I wonder if they are damaged

With respect to checking voltage, I guess then the way to test them would be to disconnect the switch for the chassis batteries and then let them sit a bit and take a reading?

I'm just a bit concerned because it's been on bulk charging now for probably 5 or 6 hours with the fan on and seemingly no progress. According to the specs, it looks like the charger circuit puts out 50 amps.
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Old 09-13-2020, 12:31 AM   #9
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Your setup for 12 volts, not 24.

Battery charging is a 3 stage procedure.

Bulk mode is as many amps as the battery can take UNTIL the volts reach 14.6. No time limit and batteries will bubble. It stirs up the acid.

Step 2 is Absorb charge is holding the 14.? voltage as the amps drop off for a set time. 4 hours is normal.

Float is a finishing charge at 13.6 volts for as long as it takes or in many cases constant.

You can run your batteries down below 50% charge. Saying you can't is a myth.

At 7 years old, your batteries are probably failing. Never discharging and recharging them causes then to fail more then running them down once in a while.

Your state of charge indicator needs to be reset. They are not exact instruments and can drift off as time goes by.
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Old 09-13-2020, 12:52 AM   #10
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Awesome! Thanks Twinboat !

And some good news, the fan finally shut off and the panel now says it's alternating between bulk and float. There was a LOT of boiling going on in the cells. Some of them were frothing. Because it ran so long, and didn't seem to make progress, I was worried that it was going to boil them dry.

Question:

I can set it to stop inverting when batteries drop to 11.8v OR I can set it to run them down to the end. Which should I choose?

Also, how does a person reset the charge indicator?

Lastly, it never used to fluctuate between bulk and float. It used to be straight bulk and then straight float (which makes sense). What could cause that? It happens very quickly on the panel and the fan never comes on. I wonder if that could be cured by 'resetting the charge indicator' ?
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Old 09-13-2020, 03:23 AM   #11
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You have over 400 AH of battery that was run down over 350 AH. If they are charging at 50 amps, you will expect at least 7 hours to replace the 350 AH.


At 7 years old, your batteries are probably failing. $600 over 7 years is cheap power, although in your case, you didn't use them.

Shut everything down for 24 hours and see if they hold 12.7 volts.

Don't change the low voltage cut off. When the inverter is running, the battery voltage reading is lower then resting voltage. All of the state of charge charts are at resting volts, not under load.

You want the cut off somewhere near 11 volts with the batteries at rest. Not 11.8 while being used. That's why the low cutoff is set so low by default.

The reset and and flashing between bulk and float may be explained in the manual. What inverter/charger do you have ?
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Old 09-13-2020, 08:36 AM   #12
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Was this a residential fridge, or an absorption fridge you were running 26 hrs on battery power?
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Old 09-13-2020, 12:44 PM   #13
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You have over 400 AH of battery that was run down over 350 AH. If they are charging at 50 amps, you will expect at least 7 hours to replace the 350 AH.
Ah..that explains it. In the past I've used the inverter for a few hours watching TV to run them down a bit. The longest I ever saw it charge for would have been about an hour. Seems I was worried about nothing.


Quote:
Originally Posted by twinboat View Post
At 7 years old, your batteries are probably failing. $600 over 7 years is cheap power, although in your case, you didn't use them.

Shut everything down for 24 hours and see if they hold 12.7 volts.
Will do shortly

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Originally Posted by twinboat View Post
Don't change the low voltage cut off. When the inverter is running, the battery voltage reading is lower then resting voltage. All of the state of charge charts are at resting volts, not under load.

You want the cut off somewhere near 11 volts with the batteries at rest. Not 11.8 while being used. That's why the low cutoff is set so low by default.

The reset and and flashing between bulk and float may be explained in the manual. What inverter/charger do you have ?
It's a Trace Legend Series I. Specifically, L1512-B15D W/SB
(1500 Watts, 12V and SB = Standby Charger or something). I don't know what the B15D means.

Quote:
Originally Posted by 96 Wideglide View Post
Was this a residential fridge, or an absorption fridge you were running 26 hrs on battery power?
No, I'm still on the Absorption fridge and I think it draws 475 watts or so.
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Old 09-13-2020, 01:15 PM   #14
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One other thing. I've shut off the main disconnect switches to the coach and starting batteries (to get a battery voltage reading off the coach batteries after resting a while). Unfortunately, this causes the 12v lights to flicker quite a bit in the coach.

Also, I just removed the cover and am checking the jumper settings.

The first jumper determines the voltage charge rate for either SLA or vented batteries. It's not jumped which means it sets the charge rate to 14.7 during bulk charging and 13.3 during float. This jumper appears to be correct.

The second jumper controls the amount of allowable battery discharge. It is set to not allow the batteries to discharge below 11.8v for more than 5 minutes.

The last jumper sets the how fast it changes from charger to inverter. It seems this will allow it to act more like a UPS. If not set (default) it will wait 200 milliseconds for AC power to stabilize before going back to charging. Otherwise it's only 30 milliseconds. I'm going to change this one because if the power fails I find it does not change over fast enough. They say not to do that if you charge with the generator. I'm guessing it's because the voltage from the generator may cause it to switch back and forth between charging and inverting very quickly?

I'm guessing that the second jumper (cutoff at 11.8v) is there to protect the batteries from damage by draining too much.
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