Expected voltage sag?

[ewarnerusa]

I've got two 6 volt GC batteries. I have an inverter just powering a laptop. It's pulling under 100 watts AC. What kind of voltage sag would you expect that to put on these batteries if they were fully charged? What would the voltage read across the battery posts?
Thanks.

[pianotuna]

Welcome to the saggy baggy elephant show Mex! (gives you my membership to validate)

[MEXICOWANDERER]

PS

For what it's worth there is a polar opposite meaning in the words

Voltage Sag

Voltage Drop

Sag is when power generation is overtaxed.

And yeah Dummy Me clicked on the topic curious as can be. 🙂

[DrewE]

ewarnerusa wrote:

brulaz wrote:

DrewE wrote:
It's unrelated to the question at hand, but I'm curious: what does the thin wire connected to the heavy jumper between the two batteries go to? I can't think of any good reason to center-tap a pair of six volt batteries in an RV, but maybe I'm missing something. At any rate, if there's any load to speak of due to whatever this wire goes to, it would inevitably cause imbalance between the two batteries.

not sure about the o.p.
but in my case that would be a battery temperature sensor for the charge controller.

OP here. It is the same for me.

Thanks for the response; I was missing something. It would have been a very long time before I guessed properly!

[ewarnerusa]

brulaz wrote:

DrewE wrote:
It's unrelated to the question at hand, but I'm curious: what does the thin wire connected to the heavy jumper between the two batteries go to? I can't think of any good reason to center-tap a pair of six volt batteries in an RV, but maybe I'm missing something. At any rate, if there's any load to speak of due to whatever this wire goes to, it would inevitably cause imbalance between the two batteries.

not sure about the o.p.
but in my case that would be a battery temperature sensor for the charge controller.

OP here. It is the same for me.

[brulaz]

DrewE wrote:
It's unrelated to the question at hand, but I'm curious: what does the thin wire connected to the heavy jumper between the two batteries go to? I can't think of any good reason to center-tap a pair of six volt batteries in an RV, but maybe I'm missing something. At any rate, if there's any load to speak of due to whatever this wire goes to, it would inevitably cause imbalance between the two batteries.

not sure about the o.p.
but in my case that would be a battery temperature sensor for the charge controller.

[DrewE]

It's unrelated to the question at hand, but I'm curious: what does the thin wire connected to the heavy jumper between the two batteries go to? I can't think of any good reason to center-tap a pair of six volt batteries in an RV, but maybe I'm missing something. At any rate, if there's any load to speak of due to whatever this wire goes to, it would inevitably cause imbalance between the two batteries.

[MEXICOWANDERER]

Copper

H2SO4

Turquoise Copper Sulfate

If you insist on having bare posts and terminals get an AGM battery. Or remove the cables and slop on the corrosion preventative paste.

[westend]

Good deal! If you haven't given the batteries a full charge yet, I'd suggest to put 14.8 - 15 V on them from the solar for a few hours and then check everything in the morning. I'd bet you'll be good to go.

BTW, nothing wrong with using a sacrificial anode on the battery tops (a penny) or sprinkle some baking soda across the tops. I've done both and it tends to keep the terminals cleaner. It may be that all of your equalization charges caused the corrosion but I think you may have another air-exchange issue that is keeping the acidic gas inside the battery cases. Good luck with the outcome!

[ewarnerusa]

Voltages are at the expected levels. Barely a blip when I flip on LED lights. Maybe a 0.1V drop when I plug in my 100 watt laptop charger. I just ran the fridge on electric, laptop charger, and TV on for almost 500 watts draw (solar panels disconnected) for several minutes and it pulled my voltage down 12.0V. I'm pleased, things seem like they're behaving like they're supposed to.

[westend]

Nice work, that's definitely a better looking situation.

What are the voltages now that you've cleaned everything up?

[ewarnerusa]

So I pulled things apart again, baking soda cleaning and scraping of corrosion again, then reassemble with dielectric grease and protectant spray. I also cleaned up the corrosion on my cable ends and applied liquid tape. Hopefully I'm good!

Cleaned up pics.

[pianotuna]

Clean the top of the battery. Make the connections. Cover the connections with a battery protectent spray available from General Motors parts supply stores.

[ewarnerusa]

I don't know where it is leaking from and it had not occurred to me before that it was. I wonder if the semi-frequent equalization cycles that I put the batteries through when trying to recover them caused the corrosion from venting? Maybe normal usage would not? I put them through 2 or 3 temp-corrected 15.5V equalization cycles this winter with a max voltage setpoint at 16.15V. It usually ran the voltage right up to that max setpoint with the temp correction (it was winter in Montana after all).

[red31]

how about using some pookey to seal the plastic lid/battery posts? or is this just leaking from the fill/check holes?