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pianotuna

Regina, SK, Canada

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Posted: 02/15/21 06:20pm Link  |  Quote  |  Print  |  Notify Moderator

PanhandlePlainsman wrote:

I need more explanation on the application of the temperature chart.


Battery charging "charts" are set up for 25C (77f) and most charts list the charging voltage at 13.5. Gassing voltage is 14.34 volts.

The speed of chemical reactions approximately doubles for each 10 degree C (18 f) that the temperature increases.

As the temperature gets higher, the charging voltage should be lower to prevent extra erosion on the positive plates. At 50 C (122 f) charging voltage is just 13.2 and gassing voltage is 13.8

As the temperature gets lower, then charging voltage needs to be higher to "drive" the charging. At -30 c (-22 f) charging voltage ought to be about 16.2. This is a problem for an RV, because the computer boards for the fridge, furnace and other devices may only be rated about 15.4 volts. The battery will still charge at a lower voltage--but it may take a lot more time.

For example, at 12.8 volts, and 25 c (77 f) it may take 168 hours to fully charge a battery.

I hope this "thumbnail" of what may happen helps.

* This post was edited 02/15/21 06:31pm by pianotuna *


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pianotuna

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Posted: 02/15/21 06:25pm Link  |  Quote  |  Print  |  Notify Moderator

wopachop wrote:

Ive got 2 GC2 from costco. Will unplug the trailer and run the furnace and things off the battery. How many amp hours should i take out before plugging the trailer in to charge? I only want to drain the batteries enough to determine if my WFCO is charging at 14+v.


I would go with voltage not amp-hours. If voltage is 11.8 under load (furnace, lights, and etc), it is time to charge.

pianotuna

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Posted: 02/15/21 06:27pm Link  |  Quote  |  Print  |  Notify Moderator

PanhandlePlainsman wrote:

The only volt meter I have now is a digital one plugged into a cigarette lighter type plug in the bedroom. That may not be sufficient.


Check it against a good volt meter. It may be just fine.

time2roll

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Posted: 02/15/21 06:39pm Link  |  Quote  |  Print  |  Notify Moderator

PanhandlePlainsman wrote:

The only volt meter I have now is a digital one plugged into a cigarette lighter type plug in the bedroom. That may not be sufficient.
All I have. Works fine.

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PanhandlePlainsman

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Posted: 02/16/21 03:11pm Link  |  Quote  |  Print  |  Notify Moderator

pianotuna wrote:

PanhandlePlainsman wrote:

I need more explanation on the application of the temperature chart.


Battery charging "charts" are set up for 25C (77f) and most charts list the charging voltage at 13.5. Gassing voltage is 14.34 volts.

The speed of chemical reactions approximately doubles for each 10 degree C (18 f) that the temperature increases.

As the temperature gets higher, the charging voltage should be lower to prevent extra erosion on the positive plates. At 50 C (122 f) charging voltage is just 13.2 and gassing voltage is 13.8

As the temperature gets lower, then charging voltage needs to be higher to "drive" the charging. At -30 c (-22 f) charging voltage ought to be about 16.2. This is a problem for an RV, because the computer boards for the fridge, furnace and other devices may only be rated about 15.4 volts. The battery will still charge at a lower voltage--but it may take a lot more time.

For example, at 12.8 volts, and 25 c (77 f) it may take 168 hours to fully charge a battery.

I hope this "thumbnail" of what may happen helps.





So are you saying at 75 degrees F that 13.6 volts is what I should be charging at to not harm the plates? (if following the red line on the chart)


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time2roll

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Posted: 02/16/21 03:15pm Link  |  Quote  |  Print  |  Notify Moderator

CA Traveler wrote:

Here you go!

[image]


Looks a bit low to me. Must be a float voltage.

CA Traveler

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Posted: 02/16/21 04:40pm Link  |  Quote  |  Print  |  Notify Moderator

OK about the chart. It's intended to show the variation across the temperature range for common temperature compensation. As such it shows 13.56V float at 77F and 13.0V at 110V. Float voltage is for a charged battery and not the charging voltage for discharged battery.

I'll look into clarifying the chart - Perhaps just show the float variation.


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time2roll

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Posted: 02/16/21 05:00pm Link  |  Quote  |  Print  |  Notify Moderator

I don't need a new chart. And unless the OP has a variable voltage charger I doubt he does either.
It is a good illustration to understand the changes.

pianotuna

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Posted: 02/16/21 05:46pm Link  |  Quote  |  Print  |  Notify Moderator

Time2roll,

Yes it is float voltage. Gassing voltage is higher. At 25C (77 f) float is 13.5 and gassing is 14.34 volts.

wopachop

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Posted: 02/16/21 06:19pm Link  |  Quote  |  Print  |  Notify Moderator

You guys were right. I cant believe it. I took about 50ah from my 210ah pack. Plug in the trailer and run out to measure amps. I think it was at 28amps and dropping. It kept lowering charge amps and never got above 13.5v.

I'm positive my voltage display shows 14.4 at times. This is with the batteries completely removed from the trailer. Always thought it was some type of timed equalizing charge.

I feel dumb. Cant believe I never noticed. I always heard negative comments on the WFCO. I thought the problem was the WFCO had too high of a float charge and would boil batteries when left on shore power for extended periods.

Hope this info helps the OP as much as it has me.

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