Fuse Use Question

[Donager]

Hi,

I tried searching the forums, but couldn't find an answer that made me comfortable.

I have a Renogy 600w solar kit with a 60A MPPT controller that I am installing on my travel trailer for a 12 volt system.

There are 6 x 100W panels with a short circuit current of 5.21A and Max series fuse rating of 15A.

The series wattage would exceed the max wattage for the controller, so I am configuring them in a Series/Parallel configuration of 3 panels each. That brings the max amperage for each series to 15.63A, exceeding the max fuse rating of a panel.

Since I am doing a Series/Parallel setup, would a single 15a fuse on the positive wire be enough? Or do I need a different fuse? I don't want to screw this up.

Thank you for taking the time.

-Mike

 

[DIYrich]

Fuse protects wires. The "continuous" current through fuse/wire should not exceed 80%, or 12 amps for a 15 amp circuit. What is the normal operating amps, not Isc?

Upgrade the wire and fuse to 12awg and 20amp to safely carry more than 12 amps on a continuous basis.

Or, 3s2p would be 10.4 amps, if the Voc of 3 panels is ok.

 

[Hedges]

Wattage is the same series or parallel.
You need to consider max input voltage allowed, min MPPT voltage, max current.
Then for the PV panels Voc, Vmp, Isc, Imp.

Spec sheets or labels are needed.

Leave 16% margin above Voc without exceeding allowed input voltage (or get temperature coefficient of Voc if you need to come closer.

 

[Donager]

I've attached the specs for the panels and charge controller

 

[mikefitz]

configuring them in a Series/Parallel configuration of 3 panels each

3 series panels in parallel, with 3 more in parallel, does not need any fuse. Only 3 strings or more in parallel need fuses. With only two strings the maximum current from the 'good' string, into the 'bad string', cannot exceed the maximum panel current, ( 5.2 amps). If it makes you happier, fit a 10 amp fuse in series with each string.
Assuming you have a 12v system, 600 watts of panel , in theory , can deliver a maximum current of 600/12 , 50 amps into the battery. In practic, with an RV application, expect 30 to 40 amps maximum.

The important fuse in the systen is the fuse in the positive feed cable from battery to controller. Use a 60 amp fuse or quality breaker as near the battery as practical.

It may be useful to consider a solar isolation switch at the input to the controller.

 

[Donager]

3 series panels in parallel, with 3 more in parallel, does not need any fuse. Only 3 strings or more in parallel need fuses. With only two strings the maximum current from the 'good' string, into the 'bad string', cannot exceed the maximum panel current, ( 5.2 amps). If it makes you happier, fit a 10 amp fuse in series with each string.
Assuming you have a 12v system, 600 watts of panel , in theory , can deliver a maximum current of 600/12 , 50 amps into the battery. In practic, with an RV application, expect 30 to 40 amps maximum.

The important fuse in the systen is the fuse in the positive feed cable from battery to controller. Usa a 60 amp fuse or quality breaker as near the battery as practical.

It may be useful to consider a solar isolation switch at the input to the controller.

thank you, I appreciate it a lot.

 

[Hedges]

PV Voc 24.3V
SCC max input voltage 140
140/24.3 = 5.76
140/(24.3 x 5) = 1.152

Up to 5s should be fine
(unless extreme cold and high temperature coefficient.

12V nominal, SCC says 60A and 800W

100W x 6 = 600W (STC) under ideal conditions. Maybe 450W to 500W when pointed directly at the sun under typical conditions.

What battery, what maximum charge current?
Multiple PV string orientations can reduce peak power & current, spread over more hours.


You can wire 3s2p, 2s3p, or 6p.

With 20 Vmp, it may be that 6p is the most efficient (least voltage conversion.)
Don't know how much difference it makes. Different configuration may be more convenient to wire.

 

[Donager]

PV Voc 24.3V
SCC max input voltage 140
140/24.3 = 5.76
140/(24.3 x 5) = 1.152

Up to 5s should be fine
(unless extreme cold and high temperature coefficient.

12V nominal, SCC says 60A and 800W

100W x 6 = 600W (STC) under ideal conditions. Maybe 450W to 500W when pointed directly at the sun under typical conditions.

What battery, what maximum charge current?
Multiple PV string orientations can reduce peak power & current, spread over more hours.


You can wire 3s2p, 2s3p, or 6p.

With 20 Vmp, it may be that 6p is the most efficient (least voltage conversion.)
Don't know how much difference it makes. Different configuration may be more convenient to wire.

Thank you for the reply.

The 3s2p works best for the layout on the Camper roof. Unfortunately, they are extremely good at placing vents in the proper location to mess up any kind of logical layout

The battery is a Litime 12V 230AH LiFePO4
I don't know what the max charge current is.

 

[Hedges]

Probably 0.5C, 115A max.
Some cells say 0.2C, 46A.
With 600W of panels, you're under that.

(If it had been smaller or different chemistry, then might have wanted to reduce charge current.)

Can you hang some panels on the side? Tilt as awning/shade over window if they cover that?
3 on roof and 3 on side, or 4 on roof 2 on side wired 2s3p.

 

[robbob2112]

Thank you for the reply.

The 3s2p works best for the layout on the Camper roof. Unfortunately, they are extremely good at placing vents in the proper location to mess up any kind of logical layout

The battery is a Litime 12V 230AH LiFePO4
I don't know what the max charge current is.

The max charge on it is 46amps, I have a version with the same BMS in it.

 

[Donager]

Probably 0.5C, 115A max.
Some cells say 0.2C, 46A.
With 600W of panels, you're under that.

(If it had been smaller or different chemistry, then might have wanted to reduce charge current.)

Can you hang some panels on the side? Tilt as awning/shade over window if they cover that?
3 on roof and 3 on side, or 4 on roof 2 on side wired 2s3p.

Unfortunately, I wouldn't be able to easily and securely do that. they will need to remain on top.