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Expected voltage sag?

ewarnerusa
Nomad
Nomad
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.
Aspen Trail 2710BH | 470 watts of solar | 2x 6V GC batteries | 100% LED lighting | 1500W PSW inverter | MicroAir on air con | Yamaha 2400 gen
60 REPLIES 60

pianotuna
Nomad II
Nomad II
Welcome to the saggy baggy elephant show Mex! (gives you my membership to validate)
Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp-hours of Telcom jars, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

MEXICOWANDERER
Explorer
Explorer
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
Explorer II
Explorer II
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
Nomad
Nomad
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.
Aspen Trail 2710BH | 470 watts of solar | 2x 6V GC batteries | 100% LED lighting | 1500W PSW inverter | MicroAir on air con | Yamaha 2400 gen

brulaz
Explorer
Explorer
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.
2014 ORV Timber Ridge 240RKS,8500#,1250# tongue,44K miles
690W Rooftop + 340W Portable Solar,4 GC2s,215Ah@24V
2016 Ram 2500 4x4 RgCab CTD,2507# payload,10.8 mpgUS tow

DrewE
Explorer II
Explorer II
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
Explorer
Explorer
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
Explorer
Explorer
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!
'03 F-250 4x4 CC
'71 Starcraft Wanderstar -- The Cowboy/Hilton

ewarnerusa
Nomad
Nomad
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.
Aspen Trail 2710BH | 470 watts of solar | 2x 6V GC batteries | 100% LED lighting | 1500W PSW inverter | MicroAir on air con | Yamaha 2400 gen

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

What are the voltages now that you've cleaned everything up?
'03 F-250 4x4 CC
'71 Starcraft Wanderstar -- The Cowboy/Hilton

ewarnerusa
Nomad
Nomad
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.




Aspen Trail 2710BH | 470 watts of solar | 2x 6V GC batteries | 100% LED lighting | 1500W PSW inverter | MicroAir on air con | Yamaha 2400 gen

pianotuna
Nomad II
Nomad II
Clean the top of the battery. Make the connections. Cover the connections with a battery protectent spray available from General Motors parts supply stores.
Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp-hours of Telcom jars, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

ewarnerusa
Nomad
Nomad
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).
Aspen Trail 2710BH | 470 watts of solar | 2x 6V GC batteries | 100% LED lighting | 1500W PSW inverter | MicroAir on air con | Yamaha 2400 gen

red31
Explorer
Explorer
how about using some pookey to seal the plastic lid/battery posts? or is this just leaking from the fill/check holes?