Fuse question

UGT

New Member
Joined
Jun 27, 2021
Messages
12
Location
Austin, Texas
I have 2 SOT 206ah lithium batteries for the basis of my solar system on my Ram Promaster van. I am in the process of purchasing the Rich Solar 400 watt kit that includes the 40 amp solar controller, two 200 watt solar panels, and the connecting wires (10 gauge) to the controller from the panels and from the controller to the battery bank 8 gauge wires. The kit is designed for series connection. The panels are 9.8 amps each. It has a 15 amp inline solar fuse on the hot from the panels to the controller. I want to connect my system up parallel. If I understand correctly then the total amperage would be double in parallel connection and would produce 19.6 amps on the hot wire to the controller from the panel. Would I not then need a larger inline fuse from the panel to the controller? I was reasoning that I would need a 25 amp inline solar fuse. Rich Solar only has fuses 15, 20 and 30 amp. No 25 amp. I can't seem to find a suitable inline solar fuse at that amperage. Is my thinking on the fuse size wrong? I would think that running this system in parallel would not be unusual rather a common setup. Can you help? thanks in advance. Yes, I am a newbie and this is my first solar adventure. My wife is skeerd I am gonna blow somethin' up. George in Austin
 

mikefitz

Photon Sorcerer
Joined
May 28, 2020
Messages
1,574
In a camper application no fuse is needed for two panels in parallel, the panel current can not exceed the maximum panel current.
I would advise a series connection as recommended by Rich. You will get a better daily yield and shaded operation will be similar to parallel conected panels. ( and you can use the supplied fuse, useless as overcurrent protection, but may make you feel better).
This article explains when fuses are need and when they are ineffective, ( but may be needed to comply with code in a dwelling)


Mike
 
Last edited:

rmaddy

Full-time Solar-powered Trailer Life
Joined
Nov 16, 2019
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3,737
Location
USA
No fuse is needed for two panels in series
You mean parallel but no fuse is needed either way with just two panels.

I agree that series would be better than parallel unless there will be a lot of shading issues on the roof of the van.
 

mikefitz

Photon Sorcerer
Joined
May 28, 2020
Messages
1,574
Thanks maddy, made the correction.
I think you will find if you carry out some tests there is little difference with 36 cell panels in a two panel array conncted in series or parallel.
Usually the series connected panels show a slightly higher output.
The other advantage of series connected panels is slightly greater daily yield, they wake up earlier and go to bed later , the cable losses are less, and the MPPT is more efficient. With grim weather, a series system of two 36 cell panels will produce some watts, a parallel system may not even start the controller.

Mike
 

UGT

New Member
Joined
Jun 27, 2021
Messages
12
Location
Austin, Texas
Thanks guys. Watched the video, very helpful. I reckon I will go with series connection. Less wires and the kit is set up for that. Just omit the fuse. I wonder why they include a 15 amp fuse in the kit anyway.
 
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