Amp Hours to Kilowatt Hours

Google knows the formula:

kilowatthours = (amphours * voltage) / 1000
200 x 12.5/1000 = 2.5 kwh

Several issues with the above approximation.. Good as an approximation but

First: Battery voltage is almost never 12
Second, if inverting to 120 at best you are 90% efficient

For this reason I use 10 volts, plus the math is easier.

BUT IT IS STILL AN APPROXIMATION.

Now, the text formula is precise.. It is also a calculus job because VOLTAGE is not constant. Thus you must intergrate as it were (you need to do some major work to find the voltage needed for the formula,, IT is very simply not 12)

Charging for 4hrs a day will not bring you battery up to 100% more like 80-85%. It takes about 24 to 36hrs to get to 100%

You're using correct basic math
But you are slowly killing your batteries
Use the generator for the big loads, your discharge level will be less
Then the four hours of recharge time will be of more benefit to your batteries

This is a situation similar to ours, this is where solar is helpful , it keeps charging and tops up the batteries if the charge rate is higher than your use rate

You can get almost the rated battery performance by just re-charging to the 90% SOC but you can only do about 12-14 cycles of 50% SOC - 90% soc before having to do a full 100% SOC. Otherwise you start doing damage to the battery.

Consider this report from Progressive Dynamics

"Progressive Dynamics ran this test on the amount of time it took a PD9155 (55-amp) converter/charger set to three different output voltages to recharge a 125 AH (Amp Hour) battery after it was fully discharged to 10.5-volts.

14.4-VOLTS (Boost Mode) – Returned the battery to 90% of full charge in approximately 3-hours. The battery reached full charge in approximately 11 hours.

13.6-VOLTS (Normal Mode) – Required 40-hours to return the battery to 90% of full charge and 78-hours to reach full charge.

13.2-VOLTS (Storage Mode) – Required 60-hours to return the battery to 90% of full charge and 100-hours to reach full charge."

This is battery charging science - not many ways to get around it...

The rule of thumb is to have a charging source capable of producing those DC VOLTAGES listed here @ 15-18AMPS DC per battery in the bank. This is how many amps the battery will pull if you hit it with 14.4VDC. Around three hours later the battery will be at its 90% charge state. The charging current will drop back as the battery starts taking on charge.

So says the battery exports on here...

Roy Ken

sh410 wrote:
Charging for 4hrs a day will not bring you battery up to 100% more like 80-85%. It takes about 24 to 36hrs to get to 100%

Depends on your converter, I can do a pair of GC-2 in six hours, 8 tops, more than that I have to kick in the #2 converter and that screws up the math big time.

What you all told me was sort of what I expected to hear. I have 1 4-D battery and a PD9280 converter/charger. We have a small 120v freezer the runs off my inverter. We are in a National Park where generator use is limited to 2 hours morning and night. I hope I don't do any serious damage to the battery using it this way for a week or so. Looking forward to getting back to shore power and back to full charge.

RoyB wrote:

The rule of thumb is to have a charging source capable of producing those DC VOLTAGES listed here @ 15-18AMPS DC per battery in the bank. This is how many amps the battery will pull if you hit it with 14.4VDC. Around three hours later the battery will be at its 90% charge state. The charging current will drop back as the battery starts taking on charge.

So says the battery exports on here...

Roy Ken

You make a common mistake in the first sentence of this paragraph.

You assume there is one and only one 12 volt battery.. You forget that there is a lot of difference between say a group 24 where Depending on your intentions 7.5 to 22.5 are the recommended charge rates,, and an 8-D where 16 to 70 is the same recommendation.

One should never say just "12 volt battery" One should always say one of the following (As, I might add the original poster in this thread did so I'd like to congratulate him)

Size group 12 volt battery (O/P said 8-D 12 volt batteries)

Or: Amp hour 12 volt battery (C/20) (160 amp hour at the c/20 rate 12 volt batteries)

That way we can compare apples to apples

I mean which holds more amp hours? A pair of 12 volt batteries or a pair of Six Volt batteries.

Now, Reread what I typed and try to answer that question.. IF you choose the sixes, You will be wrong,,, If you choose the 12's. Likewise, For I hae not given you sufficient information to make that decision.

wa8yxm wrote:

RoyB wrote:

The rule of thumb is to have a charging source capable of producing those DC VOLTAGES listed here @ 15-18AMPS DC per battery in the bank. This is how many amps the battery will pull if you hit it with 14.4VDC. Around three hours later the battery will be at its 90% charge state. The charging current will drop back as the battery starts taking on charge.

So says the battery exports on here...

Roy Ken

You make a common mistake in the first sentence of this paragraph.

You assume there is one and only one 12 volt battery.. You forget that there is a lot of difference between say a group 24 where Depending on your intentions 7.5 to 22.5 are the recommended charge rates,, and an 8-D where 16 to 70 is the same recommendation.

One should never say just "12 volt battery" One should always say one of the following (As, I might add the original poster in this thread did so I'd like to congratulate him)

Size group 12 volt battery (O/P said 8-D 12 volt batteries)

Or: Amp hour 12 volt battery (C/20) (160 amp hour at the c/20 rate 12 volt batteries)

That way we can compare apples to apples

I mean which holds more amp hours? A pair of 12 volt batteries or a pair of Six Volt batteries.

Now, Reread what I typed and try to answer that question.. IF you choose the sixes, You will be wrong,,, If you choose the 12's. Likewise, For I hae not given you sufficient information to make that decision.

The OP stated: "I have a 4-D 12 volt battery in my fiver."