Wire sizing for battery bank

[eshorvath]

Hi all! I am new here and had a quick question. I am wiring 3 12 V 69 Ah deep cycle batteries in parallel connected to a charge controller. The charge controller is rated for 15 A at 12 V, the batteries are sealed AGM designed for solar arrays, and the one solar panel I am using is 224 W with Isc = 15A. I am not using an inverter, as the load is entirely DC. The load is ~200-250 W. My question is: What gauge wire should I use to wire the three 12 V 69 Ah batteries in parallel? Any input would be appreciated, and if you have any further questions I am happy to answer! Thank you

[Sunking]

The charge controller is rated for 15 A at 12 V, the batteries are sealed AGM designed for solar arrays, and the one solar panel I am using is 224 W with Isc = 15A.

You got problems That 224 watt sounds like panel made for grid applications which is fine if you are using a MPPT controller. But you are using a PWM controller and you panel's Imp current will be around 13 to 14 amps which means at 12 volt x 13 amps = 156 watts from a 224 watt panel. That will only support two of your batteries barely. A 224 volt GT panel requires a 20 amp MPPT controller for an output of 19 amps.

Minimum wire size between controller and batteries needs to be #12 AWG. Minimum between the battery and load device is 10 AWG.

[eshorvath]

You got problems That 224 watt sounds like panel made for grid applications which is fine if you are using a MPPT controller.

Ok sorry I didn't add that, but my charge controller IS Max Power Point Tracking. I am using this controller:

http://www.morningstarcorp.com/products/sunsaver-mppt/

I made a mistake on the panel specs from before. The specs on the panel are:
Voc = 36.6 V
Isc = 8.33 A
I believe the Imax was around 15A?

Also, for my cc, the battery is connected to the controller which controls the solar input and the load output. And I am mostly concerned about the wire size from battery to battery.

[Sunking]

Ok sorry I didn't add that, but my charge controller IS Max Power Point Tracking. I am using this controller:

http://www.morningstarcorp.com/products/sunsaver-mppt/

Good controller, but too small for your panel 240 watt panel. MPPT controllers Output Current = Panel Wattage / Battery Voltage. 244 watts / 12 volts = 20 amps. That is why it says in the specifications 200 watt maximum Input at 12 volt battery. It wil work but waste 40 watts or your panel and will clip at 15 amps output at 12 volts

I made a mistake on the panel specs from before. The specs on the panel are:
Voc = 36.6 V
Isc = 8.33 A
I believe the Imax was around 15A?

Isc is current short circuit = 8.33 amps, and Imax means Imp or current at maximum power = about 7.5 amps. Isc is always less than Isc or Imax.

Also, for my cc, the battery is connected to the controller which controls the solar input and the load output. And I am mostly concerned about the wire size from battery to battery.

You don't use the Load Output on the controller for anything. It is only rated 15 amps max and at 12 volts means no more than 180 watts. You want 200 to 250 and would burn it up if you tried. Try reading the MANUAL & Specs before you buy things.

[eshorvath]

Good controller, but too small for your panel 240 watt panel. MPPT controllers Output Current = Panel Wattage / Battery Voltage. 244 watts / 12 volts = 20 amps. That is why it says in the specifications 200 watt maximum Input at 12 volt battery. It wil work but waste 40 watts or your panel and will clip at 15 amps output at 12 volts



Isc is current short circuit = 8.33 amps, and Imax means Imp or current at maximum power = about 7.5 amps. Isc is always less than Isc or Imax.

You don't use the Load Output on the controller for anything. It is only rated 15 amps max and at 12 volts means no more than 180 watts. You want 200 to 250 and would burn it up if you tried. Try reading the MANUAL & Specs before you buy things.

My load is not fixed. It will never reach the max watts. Plus the load is not only 12V. There is also a 5V bus. I already know my system works with a 15A max charge controller. I was just giving a rough estimate of the max load for the wire calculation. The load output on the controller is in fact used and I am obviously fusing it to save the controller from burning up if it ever got to 15 A for some reason. Also I am aware that the solar panel is too large, but it was free, so I am using it. Due to the current output on the panel, it will be fine. I am more interested in the wire sizing between the batteries and between other components than anything else.

[Sunking]

I am more interested in the wire sizing between the batteries and between other components than anything else.

Minimum 12AWG.

[SunEagle]

His 15amp charge controller is still too small for a 224watt panel charging a 12volt battery.

The charger specs show 200 watts max for 12 volt battery and 400 watts for 24volt battery.

[Sunking]

His 15amp charge controller is still too small for a 224watt panel charging a 12volt battery.

The charger specs show 200 watts max for 12 volt battery and 400 watts for 24volt battery.

He does not care. He is using the Load Port on the controller. I tried, but it did not sink in. Example if using the Load Port, which is useless, you do not need a fuse because the load port is already fused. Its all in the manual along with wire sizes.

[SunEagle]

He does not care. He is using the Load Port on the controller. I tried, but it did not sink in. Example if using the Load Port, which is useless, you do not need a fuse because the load port is already fused. Its all in the manual along with wire sizes.

I agree you shouldn't use the load terminals on just about any cheap CC units. But with the Morningstar I would say a couple of low wattage lights would be fine.

The installation manual is a little confusing because it does show an external fuse in the "load" circuit on page 22 connected to the + terminal and then shows a fuse on page 27 connected to the - terminal (which is incorrect). It goes on with the confusion by stating to install a 25amp fuse in both the Battery and Load circuit but later it states the Load should not exceed 15 Amps.

That could be a little misleading for some people.

[Sunking]

I agree you shouldn't use the load terminals on just about any cheap CC units. But with the Morningstar I would say a couple of low wattage lights would be fine.

The installation manual is a little confusing because it does show an external fuse in the "load" circuit on page 22 connected to the + terminal and then shows a fuse on page 27 connected to the - terminal (which is incorrect). It goes on with the confusion by stating to install a 25amp fuse in both the Battery and Load circuit but later it states the Load should not exceed 15 Amps. .

The fuse or breaker you install between the battery and cc protect the Load Terminal in addition to internal OCP. You are just asking for trouble using the load port. Better used as a signal for a LVD.

[SunEagle]

The fuse or breaker you install between the battery and cc protect the Load Terminal in addition to internal OCP. You are just asking for trouble using the load port. Better used as a signal for a LVD.

I understand the need for the fuse between the CC and Battery.

I am just saying the installation manual for that CC is confusing by not only showing a fuse in the load circuit but showing it wired to the positive terminal in one figure and the negative terminal in a different figure. That is a typo and can be confusing to most people.

[Sunking]

I understand the need for the fuse between the CC and Battery.

I am just saying the installation manual for that CC is confusing by not only showing a fuse in the load circuit but showing it wired to the positive terminal in one figure and the negative terminal in a different figure. That is a typo and can be confusing to most people.

Yes I agree.