Battery Question...

[Nefariis]

I thought I read somewhere that charge controllers only charge at 10% of the max ah's of the battery bank (or at least that's whats recommended).

Any truth to that?

Thanks

[inetdog]

I thought I read somewhere that charge controllers only charge at 10% of the max ah's of the battery bank (or at least that's whats recommended).

Any truth to that?

Thanks

What is recommended varies with the type of battery and the degree of monitoring of the battery temperature, etc.

For Flooded Lead Acid (FLA) the minimum for good electrolyte mixing is C/12. The maximum to avoid battery plate damage, when applied regularly, is C/6. Your C/10 falls right in the middle of the two.

For AGM batteries with their lower internal resistance, C/4 is not unreasonable and one deciding factor for AGM batteries is if you have a very limited number of solar hours during which to complete the charging. With proper monitoring and temperature compensation in the CC, a charge rate of C is possible for some SLA battery banks.

For GEL, which are not recommended for PV, a maximum rate of C/20 is recommended unless the specific manufacturer specifies otherwise.

[Nefariis]

Alright, so if my panel is set up at 700 watts at 18v's or roughly 40 amps - I would need roughly a 400 ah battery bank to make use of the array efficiently?

I understand energy loss btw, I'm just trying to keep the math easy.

Thanks again

[Sunking]

Alright, so if my panel is set up at 700 watts at 18v's or roughly 40 amps - I would need roughly a 400 ah battery bank to make use of the array efficiently?

I understand energy loss btw, I'm just trying to keep the math easy.

Thanks again

No not at all. It depends on the charge controller type you are using. If using PWM INPUT CURRENT = OUTPUT CURRENT. So for your 700 watt array with 40 amps in you get 40 amps out at 12 volt = 480 watts.

With MPPT OUTPUT CURRENT = PANEL WATTAGE / NOMINAL BATTERY VOLTAGE = 700 watts / 12 volts = 58.3 amps.

[Nefariis]

Ok I have a 60a MPPT controller

So can I expect that my panels will charge my battery bank at 40-50amps?

and last question

Is it just a straight across conversion - to recharge 220 ah battery bank at 40 amps takes ~ 5.5 hours (plus what ever inefficiencies are in the system)?

Thanks

[Sunking]

Ok I have a 60a MPPT controller

So can I expect that my panels will charge my battery bank at 40-50amps?

and last question

Is it just a straight across conversion - to recharge 220 ah battery bank at 40 amps takes ~ 5.5 hours (plus what ever inefficiencies are in the system)?

Thanks

No Sir, not straight across as batteries have a charge efficiency of about 80% and a Saturation time. Recharge time with a 3-stage charger is Hours = [AH / A] x 1.2 + 6 hours saturation on Absorb. So if you had a dead 220 AH battery with a 50 amp charger would take roughly [220 AH / 50 A] x 1.2 + 6 hours = 11.28 hours.

You can expect up to 40 to 50 amps max assuming you have the panels configured correctly at the right tilt and orientation around solar noon with crystal clear skies. That is assuming your batteries are demanding full charge in the BULK charging stage.