solar panel fuse

30boat

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I have a single 50 W panel with two simple controllers, one for each battery. One has been blowing it's 5 amp fuse and then the 10 amp one that replaced it. I now put a 15 amp fuse on. The other controller had one all the time. The problem is that I may have damaged the battery that was showing 10.2V. Could a duff battery be the cause for the fuses blowing?
 

jac

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When you say a single panel wired to two simple controllers i'd be interested to see how that's wired as 50w shouldn't blow a 5 amp fuse and def shouldn't blow a 10 A one.

If you haven't got any blocking diodes I suspect that the "duff" battery might have been fed by the good battery, back through the solar wiring. As a 12v battery is certainly capable of producing more than 10A it would blow those fuses.

SO - Are there blocking diodes ( or anything else) stopping the batteries paralleling via the solar charge wire?
 

30boat

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When you say a single panel wired to two simple controllers i'd be interested to see how that's wired as 50w shouldn't blow a 5 amp fuse and def shouldn't blow a 10 A one.

If you haven't got any blocking diodes I suspect that the "duff" battery might have been fed by the good battery, back through the solar wiring. As a 12v battery is certainly capable of producing more than 10A it would blow those fuses.

SO - Are there blocking diodes ( or anything else) stopping the batteries paralleling via the solar charge wire?

It's possible that the good battery is trying to charge the bad one.I'm going to get a twin battery regulator anyway.This set up was only a stop gap thing.I have no ideia if the controllers have blocking diodes in them.The arrangement worked for a good while though.
 

Stemar

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It's generally a bad idea to replace a blown fuse with a bigger one. Sooner or later, you'll get to the point where the fault will be carrying enough current to start a fire.

If the original 5 amp fuse lasted for a good while, something's gone wrong and I'd suspect the controller that's blowing the fuse.

I've got one of these [/FONT]http://www.sunstore.co.uk/EP-Solar-Duo-Battery-Solar-Charge-Controller-12-24v-10A.html in charge of my 40w of panels; it won't break the bank and it does a great job of charging the starter battery until it burps then turning its attention to the domestic one. I did it that way round because I figured that if the lights don't work, I can start the engine to top up the domestic battery, but it's a bit more awkward if the engine won't go! (yes, I can start with the domestic battery easily enough, but the cables are longer, so there isn't quite as much umph)
 

sarabande

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at the weekend i saw a small solar panel being set up to trickle charge a twin battery system.

Amazed was I to see that the biggest voltage output could reach 18v ! OK, on a 10W panel that's not a lot of load, but suspect that solar panels often output => the 14.5v of an alternator or charger.
 

William_H

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at the weekend i saw a small solar panel being set up to trickle charge a twin battery system.

Amazed was I to see that the biggest voltage output could reach 18v ! OK, on a 10W panel that's not a lot of load, but suspect that solar panels often output => the 14.5v of an alternator or charger.
Sarabande your sentence is very confusing. A solar panel will show 18 to 20 volts without a load. If you short out the leads it will show 0 volts but about half an amp will flow. (In full sunlight) he panel has an internal resistance which limits max current and means this test is not harmful.
Now the panel when connected to a battery directly will have the terminal voltage of the battery if measured. The current into the battery will be nearly the half amp capability of the panel. ( almost regardless of battery charge state.) Now if you have a decent sized battery (or batteries connected) then the battery voltage will never rise much above 14v even with long term charging from the panel. Hence large battery small panelis ok no controller.
But if you have a larger panel smaller battery the panel current going constantly into the battery can over charge ,boil or cook the battery. So yes the voltage is not regulated or can be much more than an alternator. But that voltage is just a max or potential voltage when connected to a battery.
The answer is a controller. These will limit the voltage of the battery (and panel) to about 14v. (rather than the available 20v). This means that as the battery is charged the current into the battery will diminish as the battery inherent voltage rises. So slower to get that last bit of charge but protected from overcharge. Controllers may have the algorythms of a smart charger to charge at a higher voltage until it detects full charge then reduce to trickle/maintenance. good luck olewill
 

jac

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Sarabande your sentence is very confusing. A solar panel will show 18 to 20 volts without a load. If you short out the leads it will show 0 volts but about half an amp will flow. (In full sunlight) he panel has an internal resistance which limits max current and means this test is not harmful.
Now the panel when connected to a battery directly will have the terminal voltage of the battery if measured. The current into the battery will be nearly the half amp capability of the panel. ( almost regardless of battery charge state.) Now if you have a decent sized battery (or batteries connected) then the battery voltage will never rise much above 14v even with long term charging from the panel. Hence large battery small panelis ok no controller.
But if you have a larger panel smaller battery the panel current going constantly into the battery can over charge ,boil or cook the battery. So yes the voltage is not regulated or can be much more than an alternator. But that voltage is just a max or potential voltage when connected to a battery.
The answer is a controller. These will limit the voltage of the battery (and panel) to about 14v. (rather than the available 20v). This means that as the battery is charged the current into the battery will diminish as the battery inherent voltage rises. So slower to get that last bit of charge but protected from overcharge. Controllers may have the algorythms of a smart charger to charge at a higher voltage until it detects full charge then reduce to trickle/maintenance. good luck olewill

Lot of sense here.

One other point re controllers - For a small panel - where figure in watts is less than 10% of the Ah of the battery then you will probably be fine to not have a controller. But get to or go over that 10% and you will need a controller. So for a typical starter battery of say 75Ah - a 7 Watt panel will be ok without a controller - if you fit a 10W panel - you will need a controller.
 
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