Thinking about getting a 24V PWM Charge Controller...

[Kugel8x57]

Thinking about getting a 24V 60Amp PWM Charge Controller as a backup to my MPPT controller.

My Battery Bank is 24v-96ah LiFePO4, 2s6p. Battery mfg recommends 14.4v-14.8v charge voltage with 10A charge current per 12v battery ==> 28.8v-29.6v charge voltage with 10amp charge current per 2s-24v string. 2s6p is the reason for the 60amp MPPT charger.

My panels will be 3s2p for Voc ~ 113v (3x37.6v). 3 x 250w per panel ~ 750w per series x 2 ~ 1500w ==> 1500w/24v = 62.5amps max and 1500w/29.2v = 51.36amps min.

I suppose I could break it up into two 30amp charge controllers feeding in parallel to the BB. This would give some redundancy, albeit at only 5amp charge current.

Reason for considering PWM backup:
- They are inexpensive.
- Although they are not as efficient as MPPT, they seem to be very reliable.
- I have a critical application where I need to keep medication cool in a refrigerator.
- Having the PWM will allow me to keep the system running while dealing with getting a replacement MPPT - vendor, warranty, etc.

Any suggestions for a PWM Charge Controller?

Many Thanks and God Bless!

Kugel

 

[Kugel8x57]

HA!! Just realized why this is not a good idea!

With my system designed for MPPT (6 x 250w, 3s2p), my wires from panels to MPPT are sized for 17amps @ 91v. This allows me to use 10Awg for the distance I have without too much Voltage drop ~ 1.8%. If I go with 24v PWM, I will have to rewire for 1s3p x 2 and each string will be 25amps @ 30v. That will put me into 4Awg for the same approximate voltage drop (2.13%)... a significant increase in wire size and cost.

So... never mind!! ?

Thanks Again and God Bless!

Kugel

 

[ghostwriter66]

HA!! Just realized why this is not a good idea!

With my system designed for MPPT (6 x 250w, 3s2p), my wires from panels to MPPT are sized for 17amps @ 91v. This allows me to use 10Awg for the distance I have without too much Voltage drop ~ 1.8%. If I go with 24v PWM, I will have to rewire for 1s3p x 2 and each string will be 25amps @ 30v. That will put me into 4Awg for the same approximate voltage drop (2.13%)... a significant increase in wire size and cost.

So... never mind!! ?

Thanks Again and God Bless!

Kugel

Glad you realized that ... good job .. good luck