Fuse sizing question

jgbagley

New Member
Joined
Mar 30, 2021
Messages
6
Hi all,
I am a solar newbie and was looking to get some recommendations from the community on what I should do to alleviate a problem of my fuses blowing frequently. I have 2 x 200W Renogy Solar Panels connected in parallel which each having a 20A solar charge controller which came with the panels. I have 2 methods of connecting the output of the charge controller to my AGM batteries:
1. The Alligator Clips which came with the solar panels
2. A ZAMP SAE Solar Port

My issue is that both of these have a inline 15A fuse on them which keeps busting. As each solar panel is 20A, my belief is that I need to replace them with 40A fuses. Is this a correct assumption? I a little confused as to why Renogy would have a 15A fuse which came with the panels which are rated for 20A, so that is making me concerned that I am not understanding something fundamental about this.

Thanks for any help you can provide!
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
8,428
200W panel / 12V battery = 16.7A, more or less depending on state of charge and battery voltage.
Charge controller rated for 20A, so ought to be fused 25% higher to prevent nuisance trips, 25A.

You connected two of these panels plus charge controllers in parallel, then to battery? Expect about 33A, which would blow a 15 or 20A fuse, probably a 25A fuse.

You can use two of the supplied wires/fuses so each panel and charge controller has its own.
You can make one heavier wire, ought to be at least 10 awg. If used on a house which is subject to NEC we would use 8 awg and 50A fuse, but for portable/mobile application 10 awg is OK (ampacity is 35A for 90 degree C insulation like house wiring). the 33A is a bit high for 12 awg.

If the two panels faced different directions that would reduce peak current and extend hours of production. e.g. oriented for 10:00 AM and 4:00 PM production, a 90 degree angle between the panels, about 0.7 times the peak current you get when both facing same direction.

Instead of clips you might get backwards one time (likely reason fuses are provided), if you get polarized plugs with ring terminals it can be plugged/unplugged when you move.

AGM batteries - how many amp hours? Do they have a rating for maximum charge current? If so, avoid exceeding that which could damage them.
 

jgbagley

New Member
Joined
Mar 30, 2021
Messages
6
200W panel / 12V battery = 16.7A, more or less depending on state of charge and battery voltage.
Charge controller rated for 20A, so ought to be fused 25% higher to prevent nuisance trips, 25A.

You connected two of these panels plus charge controllers in parallel, then to battery? Expect about 33A, which would blow a 15 or 20A fuse, probably a 25A fuse.

You can use two of the supplied wires/fuses so each panel and charge controller has its own.
You can make one heavier wire, ought to be at least 10 awg. If used on a house which is subject to NEC we would use 8 awg and 50A fuse, but for portable/mobile application 10 awg is OK (ampacity is 35A for 90 degree C insulation like house wiring). the 33A is a bit high for 12 awg.

If the two panels faced different directions that would reduce peak current and extend hours of production. e.g. oriented for 10:00 AM and 4:00 PM production, a 90 degree angle between the panels, about 0.7 times the peak current you get when both facing same direction.

Instead of clips you might get backwards one time (likely reason fuses are provided), if you get polarized plugs with ring terminals it can be plugged/unplugged when you move.

AGM batteries - how many amp hours? Do they have a rating for maximum charge current? If so, avoid exceeding that which could damage them.
Thus far, I have been using the polarized plugs with the ring terminals which was pre-installed on my travel trailer from the factory (The Zamp SAE Port) and I am using 10AWG solar cable to run the connection from the charge controllers to the battery.
Here is a link to the AGM batteries I have: 2x 100Ah 27 AGM. I don't see any details on a maximum charge current on their spec sheet, but I have read that you should limit the charging current to .2C (20%) of the batteries capacity. As I have 200Ah of batteries, that would be a 40A limit.
 

Alphacarina

Solar Enthusiast
Joined
Feb 22, 2021
Messages
215
The fuse is in the alligator clips which come with the panels.
View attachment 51742
As a general rule, fuses are sized to protect the wire in the circuit - You want the fuse to blow before the insulation on the wire starts to melt, which could cause a fire. The wires on those alligator clips look to be quite small, possibly 16 gauge? They were obviously designed for the output of only one single panel, so the 15 amp fuse probably should not be replace with anything larger. If you're going to connect two panels in parallel, you need to discard that cable and use something designed for higher currents - 10 gauge would probably be a good place to start and then you could use a 30 amp fuse

Don
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
8,428
Data sheet:


Says initial current <= 0.2 x 20 hour amp-hour rating, 13.9 to 14.2V (at 25 degrees C.)
Try to keep battery at room temperature during charging, unless charge controller has a battery temperature sensor.

The Zamp link you gave says 12 awg. If that had 90 degree C wiring (typical THHN/THWN house wiring) it would have ampacity 30A but NEC limits to 20A fuse. Not on a house, it could be used to 30A. But the gizmo's zip-cord wire probably can't take the temperature. If you can bypass stuff that is small gauge, low-temperature insulation, the you could make a 40A system. Make sure connectors can handle it too. Just making two parallel circuit might be easiest, using the stuff you've got already.
 
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