Battery Charging Problem

[JACA]

Last weekend, we were boondocking for one night, not too far from home. Overnight, we used the inverter and used up the batteries. In the morning, I noticed that even after starting the generator, the batteries did not charge up. So, I started the coach engine, and we headed home. By the time we arrived home, a couple hours later, the house batteries were charged - 13.5 volts.

After arriving back home, I plugged into shore power (regular household outlet, 15 amps), and noticed that the "AC charge in" light was not activated. I'm only using this shore power to charge up the house batteries, not to run anything.

I have a 2007 Dynaquest 340XL, with a Xantrex SW3012 3000watt inverter/charger, with Xantrex system control panel.

I have checked the electrical outlet in my garage and the extension cord from that outlet plugged into a dogbone/adapter (15amp to 50amp). When I plug the cord in, I can hear the automatic transfer switch clicking on, so I know that's good.

At the Xantrex control panel, the mode setting is "enabled" for AC charge, but the green light is not on.

I went for a drive for a few miles, and I could see that the chassis engine is charging the house batteries while driving. When I got back home, I plugged into shore power again, and confirmed that no power is coming into the coach, as shown by the control panel. I also started the generator, ran it for about 30 minutes, and confirmed that power from the generator is also not charging the batteries.

I have checked all breakers and fuses and ensured they are good. I have also reset the battery disconnect switches, and reset the master switch at the PDM. By reset, I mean, turning them off, waiting about a minute or so, and turning back on.

So, bottom line: neither shore power nor generator are showing as "AC charge" on the Xantrex control panel, and the house batteries are not charging.

Does anyone have any ideas about what else I should try testing/checking?

[TitanMike]

Perhaps a reset button on the inverter if it's also the charger??

[JACA]

TitanMike, yes I already reset the inverter/charger a few times. When I do the reset, I can hear (fan motor) and see it (lights) as it reboots itself. There is only one breaker for the inverter/charger, and that is good too.

Still...no AC charge in from shore power or generator.

[Herk7769]

If the coach battery shorted or was discharged below 8-9 volts, the inverter/charger will not connect to it in order to save itself from connecting to a direct short or perceived direct short (very high initial current draw).

Remove the coach battery from the system (take the ground cable off) and them measure the output of the inverter/charger. If it is 13.5 volts or more; replace the battery.

If it is VERY dead, but not shorted internally, you MAY be able to "save" the battery with a dedicated 4 stage battery tender. You must remove the battery from the camper and floor charge it in a safe place. It could take many days to dissolve the caked on lead sulphate on the plates.

http://batterylifesaver.com/

[JACA]

Herk7769, I did think about scenario, since on Sunday morning, after running the inverter all night, the coach batteries were undervoltage. The Xantrex control panel said the voltage was around 9.8 volts. However, the Xantrex SW3012 is designed to also charge batteries that are depleted down to 5 volts.

Based on what I described, do you think it's still worth disconnecting the 6 batteries, and test each one?

[Herk7769]

Originally Posted by JACA

Based on what I described, do you think it's still worth disconnecting the 6 batteries, and test each one?

Yes I do.

They should be load tested at a battery shop to confirm how must capacity they have lost and if it is worth trying to recover them.

With the batteries disconnected, are you getting 13 plus volts from the inverter/charger?

I was able to "save" my dad's car battery that he routinely let die due to not driving it (when he drove that is). Took about three weeks on a 4 stage charger and its been running the car terrific for the last 18 months (since he gave me the car - at 96 he can't handle the OTHER drivers).

[JACA]

Okay, I think I've narrowed down where the problem is. I disconnected the Xantrex inverter/charger from the house batteries. With a multimeter, I tested the DC terminals from the inverter/charger, and it showed only about 2.5 volts, but jumping around a bit.

So, this seems to tell me that my house batteries are not the problem, but there is a problem with my inverter/charger on the "AC charge" function. There is a green light on the front of the unit for "AC charge" and it is NOT lit.

I've already rebooted the system a few times, and I've also reset the AC breakers on the side of the unit.

Any other thoughts or ideas, short of taking the Xantrex in for service?

[JACA]

As follow-up, I tested my 120v AC at my shore power outlet, then the extension cord, then at the automatic transfer switch, then at the input to the Xantrex inverter/charger. All good, showing 120v.

And previously, I confirmed that, with the house batteries disconnected, the DC output on the Xantrex only showed about 2.5v, not the 13+ volts that it should have shown.

So, this narrows it down to a bad Xantrex unit. I've checked all the settings again to make sure everything is in the correct mode/position. Unfortunately, I also have no faults or warnings showing, so the system is not giving me any hints as to what the problem might be.

My plan is to take the Xantrex to a repair shop, and hope that they can repair it. In the meantime, I'm going to buy a new Xantrex SW3012, to replace the old one while it's in the shop. If the old unit cannot be repaired, then I'll still have a new one. If the old unit can be repaired, then I'll stack the two units to increase my power capabilities.

[Herk7769]

Originally Posted by JACA

If the old unit can be repaired, then I'll stack the two units to increase my power capabilities.

I am not so sure this is a good idea.

Are you thinking you can draw double the amps from 2 inverters than you can draw with just one?

The inverter/charger's amp size is based on your battery bank's ability to supply power, not the ability of the inverter to deliver it.

For example, if your battery bank can deliver 100 amps @ 12 volts maximum that means you can only make 1200 watts maximum. A 1500 Watt inverter is plenty in this case. Having 3000 watts of inverter capability won't change that. 1200 Watts in; 1175 or so Watts out due to internal conversion loss.

Additionally, Doubling up the inverter will double the internal loss just being connected to the battery bank. Doubling the loss without a corresponding increase in performance is just wasted battery capability.

Just keep the repaired one as a spare. You may need it.

[JACA]

Herk, thanks for insight.

So, what would be the benefit to stacking two inverter/chargers? The Xantrex literature talks about that quite a bit.

[Herk7769]

Originally Posted by JACA

Herk, thanks for insight.

So, what would be the benefit to stacking two inverter/chargers? The Xantrex literature talks about that quite a bit.

Always interested in learning something new.
I would love to see the reference.

https://www.manualslib.com/manual/19...page=15#manual

So I found the reference and you can do this with a special stacking cable.

The application is for a wind/solar/battery homestead application.

Not at all practical in an RV.

[JACA]

Herk, my plan is to eventually put several solar panels on the roof of my motorhome, and then switch my 6 AGM coach batteries to lithium.

Basically, I want to be able to go off-grid for long periods of time, without having to rely on my generator. I've seen a few videos of RVers who have stacked inverter/charger units and were happy with it. Again, I'm not sure exactly what the benefits are, but some folks seem to think it was worth the effort and expense.

[Herk7769]

https://www.manualslib.com/manual/19...page=14#manual

It is used primarily to power 240 volt appliances from the batteries according to Xantrex. Again for use in an off grid homestead.

Obviously your camper; your money.

Just saying you will most likely be disappointed in your bang for the buck.

Happy trails,
Herk

[TitanMike]

Originally Posted by JACA

Herk, my plan is to eventually put several solar panels on the roof of my motorhome, and then switch my 6 AGM coach batteries to lithium.

Basically, I want to be able to go off-grid for long periods of time, without having to rely on my generator. I've seen a few videos of RVers who have stacked inverter/charger units and were happy with it. Again, I'm not sure exactly what the benefits are, but some folks seem to think it was worth the effort and expense.

Rather than "stacking" inverters for more power I'd personally prefer only one inverter that meets the total need for my TT's power. Since I have a 30 amp service that means a single 4kw inverter would be enough.

Costs are coming down every year so a single Inverter is very doable. Stacking them in my mind only means twice the trouble when things go wrong.

That said, I also think a better route would be to use the large inverter only when running high draw appliances. For evening TV watching and such I'd have a small inverter that handles the small load and conserves battery power.

[Herk7769]

Originally Posted by TitanMike

Rather than "stacking" inverters for more power I'd personally prefer only one inverter that meets the total need for my TT's power. Since I have a 30 amp service that means a single 4kw inverter would be enough.

Costs are coming down every year so a single Inverter is very doable. Stacking them in my mind only means twice the trouble when things go wrong.

That said, I also think a better route would be to use the large inverter only when running high draw appliances. For evening TV watching and such I'd have a small inverter that handles the small load and conserves battery power.

So, to use 4KW of AC (4,000 / 120 volts) = 33 amps of AC, you would need to supply it with 330 amps of DC from your batteries.

The more amps you demand from your batteries, the lower the available capacity under load. (see attached graph for amp load vs capacity destruction).

So to keep capacity destruction to a manageable level, say 50%, the maximum current draw per 100AH of battery capacity would be about 35 amps.

That means you would need 330/35 = 10 100AH batteries to supply 4KW for about 3 hours.

I had a 1000 watt inverter in my 30 amp camper (150AH battery bank - 2 75AH Group 24 Marine batteries) and boondocked regularly for months at a time.

Plenty of power for a CPAP machine, TV, Computer, and phone charging; just used propane for heat, fridge, coffee making, and hot water. Generator or solar to recharge during the day.

That's another thing. It could take a few days to recharge that much battery bank to full power

[TitanMike]

Originally Posted by Herk7769

So, to use 4KW of AC (4,000 / 120 volts) = 33 amps of AC, you would need to supply it with 330 amps of DC from your batteries.

The more amps you demand from your batteries, the lower the available capacity under load. (see attached graph for amp load vs capacity destruction).

So to keep capacity destruction to a manageable level, say 50%, the maximum current draw per 100AH of battery capacity would be about 35 amps.

That means you would need 330/35 = 10 100AH batteries to supply 4KW for about 3 hours.

I had a 1000 watt inverter in my 30 amp camper (150AH battery bank - 2 75AH Group 24 Marine batteries) and boondocked regularly for months at a time.

Plenty of power for a CPAP machine, TV, Computer, and phone charging; just used propane for heat, fridge, coffee making, and hot water. Generator or solar to recharge during the day.

That's another thing. It could take a few days to recharge that much battery bank to full power

No problem with LiFePo4 batteries.

Recharge in a fraction of the time for FLA as there's less wasted energy.

BTW, when running my AC and Microvave combined only draw 23 amps.

[Herk7769]

Originally Posted by TitanMike

No problem with LiFePo4 batteries.

Recharge in a fraction of the time for FLA as there's less wasted energy.

BTW, when running my AC and Microvave combined only draw 23 amps.

So how many LiFePo4 batteries do you think you need to supply 330 DC amps?

[kcmusa]

Originally Posted by Herk7769

So how many LiFePo4 batteries do you think you need to supply 330 DC amps?

look at it this way, how long do you want to power your load?


1 battle born 100 ah battery specs out with the BMS at 100 amps continues.
so you need 4 to supple 330 amps.


so 400ah of battery, 330 amp load, you get about 70 min of operation.

[TitanMike]

Originally Posted by Herk7769

So how many LiFePo4 batteries do you think you need to supply 330 DC amps?

First, the 330 amp load you referred to is about 40 amp more than will ever be drawn to power an RV 30 amp supply without tripping the main breaker.

Since max load will be 300 amp or less, and with most 100 amp LiFePo4 batteries, a 1C discharge rate is possible. Therefore only three batteries minimum.

As for running A/C, I personally don't camp where I need A/C 24/7 and have no intention to run A/C from an Inverter. A residential refrigerator perhaps (I already run a residential freezer in my outside kitchen on inverter using portable solar with 2 Battleborn batteries.

[Herk7769]

Originally Posted by kcmusa

look at it this way, how long do you want to power your load?


1 battle born 100 ah battery specs out with the BMS at 100 amps continues.
so you need 4 to supple 330 amps.


so 400ah of battery, 330 amp load, you get about 70 min of operation.

The curves below show they hold their voltage way better than lead acid at higher discharge currents and recharge faster as well.

Still, a lot of money for an hour and a half of air conditioning.