Battery Question

[CavemanCharlie]

I converted my TT to 2-6 volt flooded golf cart batteries and a upgraded converter from Best Converters. This was about 2 years ago. I dry camp once and awhile but, not to often. I have been very happy with this set up.

Last fall on my last trip of the season I was going to dry camp and when I got to the park I was low on voltage. I was shocked and a little worried. When I got home and put the TT in the shed for the winter I cleaned the posts and added water. The water level was not below the cells though it was a little low. I figured I must have made a mistake and not had the TT plugged in all the way before I left for my final trip of the season and that is why I had low voltage that time.

I've been keeping a eye on the voltage all winter as I usually do. I don't leave the converter on. It doesn't like to go into float mode. So, I flip it on once every few weeks to charge things up hen turn it back off.

I charged everything up about 3 weeks ago when it was 15 degrees f outside then shut the converter down . The voltage hovered around 12.9-13 volts for the first 2 weeks. This week the temp went up to 40 degrees f outside.

My battery voltage is now 13.9 volts :E with the converter off and no load on the batteries.

Is this normal ? I can't seem to find a answer on the internet.

(I wonder if the cheap volt meter that I have plugged into the cigarette outlet inside the TT is acting up ? )

Thank you for any responses you can give.

[Harvey51]

In my experience the battery voltage chart only becomes fairly accurate 8 hours after all charging has stopped. The hydrometer measurement is awkward in a battery compartment. What works nicely for me is a battery monitor. Even my cheapo $20 eBay one gives me a sufficiently accurate % of full charge all the time.

[westend]

Everything else seems to run fine this way

You could find out for sure with a hydrometer and a meter. If you rely on the plug in voltage meter, you really don't know if your batteries are ever getting fully charged.

[atreis]

Well, okay, I had assumed they were fully charged. 🙂 Not being fully charged would be another reason for the fast drop to 12.1 V.

[CavemanCharlie]

atreis wrote:
My AGM batteries usually read 13.7 volts. When I turn something on they'll drop pretty quickly to 12.8-12.9 and decrease very gradually from there.

If yours drops to 12.1 as soon as you turn the furnace on, either there's a large voltage drop for some reason (wire too small) or the batteries have a lot of internal resistance (they're nearly shot).

Well, it had been a couple of weeks since they were charged completely up before I performed my test. I hope they are not shot they are only 3 years old.

I know the furnace fan always runs a lot faster when I am plugged into shore power then what it does from the batteries. But, I can go for 3 days without them getting run down if I am careful and don't use the furnace too much. The batteries are at the front of the TT and the furnace is near the back right next to the power converter. I always just figured the wire was too small and too long. I could use some new ends soldered on the ends of my cables but, I usually don't need to run the furnace when I'm dry camping anyway and it is the biggest draw. Everything else seems to run fine this way.

[atreis]

My AGM batteries usually read 13.7 volts. When I turn something on they'll drop pretty quickly to 12.8-12.9 and decrease very gradually from there.

If yours drops to 12.1 as soon as you turn the furnace on, either there's a large voltage drop for some reason (wire too small) or the batteries have a lot of internal resistance (they're nearly shot).

[CA_Traveler]

You've confirmed that it's surface charge.

"This is what I found out. The voltage read 13.6 volts at 10:15 PM as soon as I turned the furnace on it dropped to 12.1 volts with the furnace running."

[CavemanCharlie]

On my second night of tests with the same conditions as the first I ran the furnace from 10 pm to 7 am. By 7 am with both the furnace and the TV on I was down to 11.5 volts. But, I was happy to see the power inverter was not signaling that the voltage was to low. With everything shut off the voltage was 12.2. This seems to be how the system always operated so I have no idea why it acted up last fall. And, I have no idea why the voltage seems so high when the battery's are at rest. But, it all works so well I guess I'll just run it. I will flip the converter / charger back on today. Charge things up, and let it go back to bed for the winter.

[CavemanCharlie]

So I slept in the camper last night it was a 35 degree night with no wind.

This is what I found out. The voltage read 13.6 volts at 10:15 PM as soon as I turned the furnace on it dropped to 12.1 volts with the furnace running. it hovered between 11.7 and 12 volts until the furnace shut off at 10:52 then it went up to 12.6. The furnace ran on and off during the night I woke up once at 1:39 and with the furnace on it read 11.8 volts. This morning with the furnace off and the TV on it read 11.9 volts. By afternoon with everything shut down it had rebounded to 12.5 volts.

I'm going to sleep in the camper again tonight but, I will use the oven to cook and that will help heat the camper up initially.

[CavemanCharlie]

wa8yxm wrote:
When you first shut off the charger the batteries retain both a Charge and what we call a "Surface Charge" They can indeed test well over 12.6 Come back in an hour or two and meter them again.

It's been a couple of weeks since I charged them and the voltage is going up. Though today when I unplugged the meter to bring it in the house to warm up it read 13.6.

When Friday comes I will go out in the shed and spend the night in the camper to see how well the battery's do.

[RJCorazza]

The old school surface charge depletion solution was to turn on headlights (10a) for 15 seconds. I suspect your meter is incorrect though.

[wa8yxm]

When you first shut off the charger the batteries retain both a Charge and what we call a "Surface Charge" They can indeed test well over 12.6 Come back in an hour or two and meter them again.

[CavemanCharlie]

Matt_Colie wrote:
I did a lot of boat work before the depression and I often saw this sort of thing.

Assuming you have a good meter for starters, mine are. It is not uncommon to see a fully charged battery at rest sitting at 13V+. With even the slightest load, the terminal will drop into the high 12s instantly. Turn on a light and they will be a 12.6 in moments. I was told by my "battery guy" (an engineer with Decca) that this is an artifact of "surface charging" where the electrolyte nearest the plates has developed a higher density and has not been redistributed yet. That redistribution can take quite a while.

The condition does not represent or cause a problem.

Matt

Thanks. Sounds like a plan. My lights are all LED and draw very little currant. I will kick the furnace on for a couple of minutes and see what the reading is after that.

I also think I will un-plug my volt meter first and bring it in the house to warm up .

[Matt_Colie]

I did a lot of boat work before the depression and I often saw this sort of thing.

Assuming you have a good meter for starters, mine are. It is not uncommon to see a fully charged battery at rest sitting at 13V+. With even the slightest load, the terminal will drop into the high 12s instantly. Turn on a light and they will be a 12.6 in moments. I was told by my "battery guy" (an engineer with Decca) that this is an artifact of "surface charging" where the electrolyte nearest the plates has developed a higher density and has not been redistributed yet. That redistribution can take quite a while.

The condition does not represent or cause a problem.

Matt

[RoyB]

Your batteries should read 12.6-7VDC when resting if they are fully charged. The 13.6VDC is coming form some sort of charging event.

When i have my batteries connected to the working converter/charger they normally read around 13.6VDC. When I shut down the converter/charger I have wait several minutes for the batteries to slowly taper down to the 12.6-7 VDC reading which is what I call resting DC voltage.

This is a handy chart showing the DC VOLTS verses the approximate charge status.



Roy Ken