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Old 02-10-2012, 22:36   #1
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Fuses for Solar panels

I am mounting 2x 100watt solar panels. I have bought a trimetric 45 am controller and have 4 gauge wire. What size of fuse and where is it best to position.

I have read someplace that if you get too large a battery bank for the panels you can not get them fully charged.

If this info is available on another thread, just point me in the right direction please.

Thanks in advance

Steve
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Old 02-10-2012, 23:40   #2
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Re: Fuses for Solar panels

The fuse goes in the positive cable between the regulator and battery at the battery end. The fuse is to protect the cable so rate the fuse size to suit the cable.
If solar is going to be the only method of charging and you have lead acid batteries you need to be able to fully recharged them in 2 days or less, any longer and they will start to sulphate and loose capacity.

T1 Terry
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Old 02-10-2012, 23:42   #3
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Re: Fuses for Solar panels

You need a fuse (or even better a circuit breaker) as close to battery end as possible.
The fuse is really to protect the wiring from high current from the battery and I would use about 20A

The manufacturers also recommend you have a fuse between the panels and the controller, but many installations omit this as unnecessary.

Make sure with the panels cannot power the house systems with the battery switches off.
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Old 02-10-2012, 23:45   #4
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Re: Fuses for Solar panels

Hi Terry,

What would you suggest for 4 gauge?

I read that the bigger the battery bank the higher the resistance. So that small solar panels can not overcome this and therfore never fully charge the batteries. Yes they would be lead acid.
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Old 02-10-2012, 23:47   #5
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Re: Fuses for Solar panels

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Originally Posted by NorthPacific View Post
I have read someplace that if you get too large a battery bank for the panels you can not get them fully charged? For my 200watts and a combined max of 11amps how big should my bank be?
Some people get very concerned about this for reasons I have never understood. It certainly not a concern with boat systems.
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Old 02-10-2012, 23:51   #6
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Re: Fuses for Solar panels

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Originally Posted by noelex 77 View Post
You need a fuse (or even better a circuit breaker) as close to battery end as possible.
The fuse is really to protect the wiring from high current from the battery and I would use about 20A

The manufacturers also recommend you have a fuse between the panels and the controller, but many installations omit this as unnecessary.

Make sure with the panels cannot power the house systems with the battery switches off.
Ok so if I put a 20amp breaker in, that could act as the on off switch to disconnect the panels from the battery?
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Old 03-10-2012, 00:01   #7
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Re: Fuses for Solar panels

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Ok so if I put a 20amp breaker in, that could act as the on off switch to disconnect the panels from the battery?
Yes that is correct and is one of the advantages of a CB.

Be aware that the solar panels will still provide voltage on the other side so some controllers will stay on for example, because they are receiving power from the panels.

It is important when choosing the CB or fuse that it has a high interrupt capacity.
4 gage wire will carry a very large current from the battery and some fuse holders and CB can melt with a large short circuit current. So the fuse blows or the CB trips, but the wire is still live.
Sometimes low value fuses and circuit breakers (like 20A) also have a low interrupt capacity.

The fuse or CB value in many ways is not very critical. If there is a short circuit there will be a very high current 100s of amps from the battery via the thick 4 gauge wire. Even a high value fuse or CB will blow in these conditions.

The other practical problem is that the CB or fuse needs to accept the thick cable.
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Old 03-10-2012, 00:18   #8
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Re: Fuses for Solar panels

SO I ask for "high value "CB 20amp is the right size?

Do you recommend anything else in the wiring from the panels to the battery Like a breaker before the trimetric controller?

Like does this make sense "connected through a fused double pole air conditioner disconnect to the batteries with 4 gauge".

Have to hit the hay but appreciate the advice!
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Old 03-10-2012, 00:23   #9
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Re: Fuses for Solar panels

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Originally Posted by noelex 77 View Post

Make sure with the panels cannot power the house systems with the battery switches off.

Is this so that you can chose to isolate the panels from the batteries using the battery switch.
Most of the schematics I have seen show the cables from the controller going direct to the battery posts via a fuse or CB.
I am planning on connecting the output from the controller to the battery switch so with this in mind, I would need to connect to the side of the switch which will be isolated with the switch in the OFF position.

With regards a CB which can accept a large cable, can you recommend any particular type/model
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Old 03-10-2012, 00:24   #10
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Re: Fuses for Solar panels

Something like this is expensive but is the ideal solution. The minimum value is 25A, but that is fine:
187-Series Thermal Circuit Breaker Panel Mount - PN - Blue Sea Systems

A very satisfactory, but cheap solution is an ANL fuse older and fuse (35A is the min value). This is a fuse not a CB, but its easy to remove (or slide) the ANL fuse out to disconnect.

http://bluesea.com/category/81/22/pr...e/overview/135

This is the fuse holder for above. It will accept large gauge wire
http://bluesea.com/products/5503
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Old 03-10-2012, 00:30   #11
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Re: Fuses for Solar panels

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Originally Posted by NorthPacific View Post
Do you recommend anything else in the wiring from the panels to the battery Like a breaker before the trimetric controller?
!
Between the panels and the controller the manufactures recommend a fuse, many boat systems don't put this in.
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Old 03-10-2012, 00:43   #12
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Re: Fuses for Solar panels

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Originally Posted by nigel1 View Post
Is this so that you can chose to isolate the panels from the batteries using the battery switch.
Most of the schematics I have seen show the cables from the controller going direct to the battery posts via a fuse or CB.
I am planning on connecting the output from the controller to the battery switch so with this in mind, I would need to connect to the side of the switch which will be isolated with the switch in the OFF position.

With regards a CB which can accept a large cable, can you recommend any particular type/model
You need to be careful connecting the panels to the battery switch. It's easy to wire it so the panels provide power to ships systems even the battery switch is off. This is particularly bad because without the voltage stabilisation of the battery in the system the voltage can rise to damaging levels.

If you connect the solar panels to the battery switch make sure this cannot happen.

The other drawback of this is sometimes when leaving the boat it's nice to turn the battery switches off, but have the solar panels still charging the batteries.
You can do this by connecting to the battery side of the battery switch, but the battery switch position then has no effect on the panels. So you need a separate switch or CB to turn the solar charging off.
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Old 03-10-2012, 00:44   #13
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Re: Fuses for Solar panels

Thanks for the info on the CB Noel, I checked the price, but in the scheme of the overall cost of panels and controller, it's not too bad, and its much more convenient.

Does the wiring still have to installed in such a way so the panels cannot charge the batteries with the switch in the OFF position?
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Old 03-10-2012, 01:00   #14
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Re: Fuses for Solar panels

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Originally Posted by nigel1 View Post
Thanks for the info on the CB Noel, I checked the price, but in the scheme of the overall cost of panels and controller, it's not too bad, and its much more convenient.

Does the wiring still have to installed in such a way so the panels cannot charge the batteries with the switch in the OFF position?
No is has to be connected to the battery side of the switch. This in effect connects it directly to battery no matter what the switch position is.
It is exactly the same (electrically) as directly connecting it to the battery its just sometimes easier.

If you connect it to the output side of the battery switch turning the switch off disconnects the panels from the battery, but with most installations leaves the panels connected to the switchboard. The panels will supply power to the switchboard just like the batteries will.
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Old 03-10-2012, 01:07   #15
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Re: Fuses for Solar panels

Thanks Noel, just gone back and seen I had mis-read your first post, (was only on my first cup of coffee), see you wrote House System.

Cheers
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