Limit on Ali meter

[Tom&Shelly]

Think we are giving our agm battery a real work out; maybe too much of one.

We have been camping at non-electric sites for the past 10 days, charging only from the truck when we change camp sites. We were trying to use our solar panel, but we are under heavy trees, there is often cloud, and the sun angle is low here at about 49 degrees latitude anyway.

Anyway, our Ali meter said we were at 87 percent, but this evening when we tried the lights, the battery voltage drops down from 12 plus to below 8 volts.

Hope we haven't done permanent damage to our battery! We will charge on the move tomorrow, and will spend a few days at an electric site so we will see what happens.

I think this shows a limitation of the Ali meter. I no longer trust it to tell us if we've used less than 50 percent of the battery.

Tom

 

[Pmullen503]

The meter has no way to tell if the battery is degrading. You would have to periodically recalibrate it for it to stay accurate.

Lithium batteries have become relatively more affordable and considering you get 80% of their capacity that's actually usable vs 50% for AGM, the price difference is even less.

 

[Tom&Shelly]

Yup, I think both are correct. The battery is 3 years old. I haven't recalibrated the meter since installing it.

On the other hand, this is the first time we've used the battery hard. Mostly we've either been at sites with shore power or lots of solar. We also kept it topped off at home, which should be okay for an agm battery.

After we get home this fall, I'll take a fresh look at lithium batteries. They didn't look attractive 5 years ago, but I agree there have been a lot of improvements in the electronics and cost.

 

[Tony Latham]

Hope we haven't done permanent damage to our battery!

I hope so too... But give the battery 45 minutes with zero load and read the voltage. If it's below 12.2 it's time.

When I built our current teardrop, LiPos didn't pencil out. They do now, but shopping while on the road for one–like you two are–is tough.

I don't know where you're at in relation to Salmon, but you could order one and have it shipped here?

Tony

 

[Tom&Shelly]

It's reading 12.6 v, with no load, this morning so fingers crossed!

Thank you for the idea about shipping one to Salmon, Tony! We'll see how this one does for now. We can get by without it. The main loss would be the fan.

Tom

 

[bdosborn-SMB]

Anyway, our Ali meter said we were at 87 percent, but this evening when we tried the lights, the battery voltage drops down from 12 plus to below 8 volts.

That's not a good sign when the battery voltage drops that much on a relatively small load. I would charge it to 100% with a charger you trust and do a load test to see how much the voltage drops with the lights on. If it's more than half a volt or so then it might be time to crack open the wallet.
Bruce

 

[bdosborn-SMB]

P.S. My neighbor bought a Li Time 100 a-hr LiFePO4 last fall and doesn't have any complaints (but he hasn't used it very much). There are a ton of cheap, generic batteries on Amazon right now so caveat emptor. Try Will Prowse on YouTube for battery reviews; he tears them apart and does load tests on them.
Bruce

 

[Tom&Shelly]

That's not a good sign when the battery voltage drops that much on a relatively small load. I would charge it to 100% with a charger you trust and do a load test to see how much the voltage drops with the lights on. If it's more than half a volt or so then it might be time to crack open the wallet.
Bruce

Thank you Bruce. We are currently at a campsite with shore power, and I did that. Didn't drop more than 0.1 volt so we may be okay, at least until we get back home in a month or so. If not we may just have to go without for awhile.

This winter. I suppose I'll need to consider upgrading to lithium. Or spend 200 dollars for another few years of agm...

Tom

 

[Tom&Shelly]

After about a day and a half of charging from shore power. I cut that source tonight and let the battery power the galley overhead lights for about a half hour. From 13.30 volts no load, right after turning off the charge (should have waited a bit but I was impatient) after about 5 minutes the battery went down to 12.90 and stayed steady for 25 minutes.

So I think we're good, especially for a 3 year old battery.

Earlier in the summer we went camping for 3 weeks with no shore power, but were mostly at sites where we could recharge from the solar panel. Then we had shore power at a few sites, then another week or so on Vancouver Island with no shore power. But the trees were taller, and the sun lower, so we never got a good charge, and only got some for a few hours from the truck while changing sites.

Also, Shelly wasn't feeling well and we used the DVD player more than usual. It has its own battery, but can and does recharge from the main battery if we don't unplug it. I now wonder if we didn't have it unplugged until it ran down, then charged it from the already hurting (more than we suspected from the Ali meter) main battery.

I'm a practicing electrical engineer, but I ain't perfect! Especially when it comes to the real world.

Tom

 

[bdosborn-SMB]

Phew, dodged that lead acid bullet.

Bruce