AGM Charging 1

[papab]

I have a lifeline 150 ah AGM battery in a campervan. I have a trimetric battery monitor. The charging system consists of the van alternator (about 14.1V, 220 Amps), a xantrex 60 amp charger, and a 100 W portable solar panel. When driving I can charger from either the charger or the van system. The charger can output at 14.3V or higher if I want to.

On a typical trip I'm not driving enuf to get it back to 100% and the battery is getting sulphated. Based on the open cell voltage it had lost capacity after some trips and I've had to condition (16V for 7 hrs) it twice this year to bring it back. I'm wondering if I should increase the voltage on the charger and/or the solar charge controller to something a little higher than the recommended 14.3V in order to charge up faster and get it back to 100% more often or at least closer to 100%.

It sounds like undercharging and conditioning is taking life out of the battery, so my thought is charging it for part of the cycle at 15V or something might be better than the alternative.

I've talked to tech support at lifeline and he wouldn't recommend anything other than what is in the manual. His suggestion was to get a generator (I'm not getting one of those obnoxious things), or accept a reduced life.

 

[itsmoked]

It's often not possible to "charge faster" as that is what you're paying for in a charger, that is, how much current it can dish out? A 200A alternator is more expensive than a 100A because of that. Likely your charger(s) is(are) supplying all the current it(they) can and raising the setpoint voltage will not provide another electron of charge, only the end point.

I'm not clear on your charge setup.

Are there THREE different chargers?
1) Solar
2) Alternator
3) Xantrex (Line powered)?

The sulfating issue is not a charge rate problem it is a: How long the bank sits before any form of charging occurs with a very strong relationship to the depth of discharge during the wait.

Then next up is, does the bank reach full charge using whatever mode of charging eventually.(?)

So the first thing to combat is discharge the bank no further than you can manage. Getting below 60% charge quickly gets you into easy sulfate land. If you do this frequently then consider a bigger bank to supply the needs with less depth of charge.

Next get things charging as soon as possible. 20 years ago the same week of the discharge was good enough. New batteries from everyone are now spectacularly inept at fending off sulfating once discharged. I see a dead battery ie one with a voltage less than 12V as being heavily damaged if not charged within 12 hours and severely damaged if not charged within 24hours. Most gel cell batteries are destroyed if left in a discharged state for more than 12 hours. Flattening modern batteries (<6V) of any kind damages them all.

So if you're draining your pack down below about 60% and not getting around to applying some sort of charge soon you will incur some capacity loss.(each cycle)

What's your typical usage profile like?

Also you should be aware that when charging you charge to a higher voltage than you float at. You should definitely charge to that "daily rate" for your bank before throttling back to the float voltage. Is that what you're doing?





Keith Cress
kcress -

http://www.flaminsystems.com

 

[papab]

Yes, there are 3 chargers, xantrex, alternator, solar CC.

My usage profile: daily use is about 30 ah (20%). A short drive or some good sun if I'm parked will get me back to 90%. That last 10% can take a while. Some days there's no sun and I don't drive. On a trip this year, with little sun and short drives it it was usually between 60-85%. This is based on the battery monitor which seems pretty close. Twice I went about 10-13 days without getting back to 100%. I did drop below 60% a couple of times in 6 weeks.

Yes I'm doing my best to charge at 14.3 when it needs charge. I'm charging at 14.4 when on the charger. It kicks down to 13.5V when the current drops to 6 A. I just figured out a way to keep the charger at 14.2 or 14.5 all the way to <0.75 amps, but I wasn't doing that last time. If driving I would switch to straight van input which was 14.1V. Sometimes the solar panel couldn't put out 14V, depending on the battery SOC and sun.

The charger is not typically at max current (60). It's a voltage source and the battery is not very often at a low enuf SOC to use the full 60 amps. The same with the alternator, the current is limited by what the battery will accept at 14.1V. I can't do anything about the alternator voltage, but I could bump the charger or the solar panel (which would only help when SOC is above 90%).

 

[itsmoked]

OK, Thanks for the clarification.

I see what's up, a large part of your charge energy goes into the battery as it reaches higher cell voltages. That's part of why the charge seems to stall out. You definitely are failing in your bank's care-and-feeding if you don't reach the "daily charge cutoff voltage" (absorption) every cycle.


Page 19 of your battery's manual is pretty clear on what's happening to your battery. The solar solution is not adequate for charging, only sort of helping to reduce the discharge rate/depth during sun and for keeping the charged battery floated.

Your Xantrex is good enough to do the job just barely but adequate. You should definitely see it performing exactly like the battery manual describes. You should use an accurate digital multimeter to follow and watch exactly what it does during an entire charge cycle to confirm it is working as needed. Check that it switches at the stated current to float and not before. Do not trust that the settings prove it!

Also check that the temperature situation is correct.. You should notice in the manual how it needs to change with ambient. THAT IS VERY IMPORTANT as otherwise you are trashing the battery in different ways depending on the temp error.

If your vehicle alternator is indeed only managing 14.1 you need to fix that somehow - it's damaging the battery!!

If the Xantrex is confirmed as working correctly you might try using an inverter off your vehicle's 12V to run the Xantex for the final correct absorption charge termination. By experimenting a little you can find the optimal switchover point in the course of the charging. Somewhere the alternator's low voltage will start tapering the charge rate prematurely. That is where the Xantrex would take over. You'd want an 800 or more watt inverter - probably go for 1,000W to support the Xantrex's load. On the up side the inverter can serve multiple purposes for you by running it off the deep cycle when you need 120VAC. You could also always run the Xantrex with the inverter to same having to mind the charging process.

I hope this battery isn't in parallel with the vehicle starting battery.

Ultimately you need a reliable workable strategy to get the charging done correctly and in a timely manner.

I had a private rail car owner install $8k worth of batteries and they roached them out in a year with inattentive charging.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[papab]

I have an inverter running from the van 12V system as you've described. The lifeline guy I talked to said that 14.1 was close enough to the 14.3 +/- 0.1 that they recommend. I also have the temperature sensor with the xantrex. I have a trimetric battery monitor which includes voltage & I've cross checked it with a DVM.
The problem is that I'm not driving long enough to get the battery back to full charge.
The xantrex drops to float when the current drops below 6A. Lifeline recommends float when current drops below 0.75A so what I've been doing is switching to the van, 14.1 at that time. I recently figured out that if I set the xantrex to gel and overide the temperature so it's set to cold I can get 14.5 so I'll try that now. I don't think it's going to make enuf of a difference tho.
I'm considering increasing the charge voltage to get a little higher charge current. I've noticed that there isn't much of a bump in current going from 14.1 to 14.4V. Maybe 15? I'm sure this isn't optimal, but I'm wondering if it might be better than the undercharging situation I'm in now.
I'm going on a trip today so I probably won't be able to respond for a week+, but might be able to read the forum.

 

[itsmoked]

I'd make sure you reach the 14.3V. I disagree it's "good enough".

Good you've fixed the 5A float issue.

15V would be bad..

Happy trails.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[mikekilroy]

i agree with itsmoked (purple star reply!): 14.3 is too low for daily charge to control sulphation. i would not be happy less than 14.4 min.

your xantrex should also be capable of weekly or so equalization to knock off sulpher build up. if not, consider changing to new one.

http://www.KilroyWasHere<dot>com

 

[papab]

Weekly equalization? Wouldn't that shorten the life? Lifeline says do it only if you have to. What happens to the battery if the voltage is you high, as long as it doesn't get too hot?

 

[mikekilroy]

"weekly or so" maybe should have been "monthly or so." Although if one has sulfated battery more often may help knock it off. Follow your battery manufacture's recommendations.

For instance, Trojan lists they would like a daily charge on their deep discharge batts to be to 14.8v so your 14.3 is too low, would undercharge them, leading to lower life and sulfation.

They recommend their equalize overcharge anywhere from 1/month to a couple times a year.

See their notes on all this here:

http://www.trojanbattery.com/tech-support/battery-maintenance/

down near bottom half of report.

http://www.KilroyWasHere<dot>com

 

[papab]

Mike, the doc you linked is mostly for FLA, trojan says do not equalize AGM.

Trojan and lifeline have very different recommendations. Lifeline does recommend 14.3, and they don't put a limit on current. Trojan recommends 20% of capacity. Trojan says do not equalize, lifeline says you can. Is the construction of the batteries very different?

What happens to an AGM battery if the voltage is too high, but it doesn't get hot?