solar panel regulator placement
Submitted: Wednesday, Dec 16, 2009 at 14:29
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outsider
G'day
I have bought a folding 80 watt solar panel. I have been playing around with it today and have noted that there is about a 1 volt difference between the voltage at the panel and the battery.
At the moment the regulator is kicking in at about 13 volts which is actually 12v at the battery due to the voltage drop, also it is backing off the charge rate too early as the voltage is higher at the panel.
Seeing the regulator is mounted on the panel I would think I would be better off moving the regulator to the battery end of the leads.
Is this thinking correct ?
Reply By: Member - John and Val - Wednesday, Dec 16, 2009 at 15:00
Wednesday, Dec 16, 2009 at 15:00
Outsider,
When charging I'd expect to see at least 13 and probably 13.5 volts at the battery (unless it's very discharged). There should be about 5 amps from the panel, so there will be some loss of voltage in the cable. This could
well account for much of the volt you are losing.
It would be preferable to have the controller close to the battery as you suggest, so that the cable loss is "upstream" of the controller.
HTH
John
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Reply By: outsider - Wednesday, Dec 16, 2009 at 15:26
Wednesday, Dec 16, 2009 at 15:26
Ok, I have re-wired it so the regulator is at the battery end and it appears to be working much better now. Charge rate has gone up from 2.5 amps to 5 amps as the regulator is now seeing the true battery voltage.
I'm surprised it mad that much difference.
The regulator has a circuit breaker built into it, now that it is at the end of 6m of cable would it be a good idea to put a fuse at the panel end in the unlikely event there is a short in the cable?
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Follow Up By: Member - John and Val - Wednesday, Dec 16, 2009 at 16:15
Wednesday, Dec 16, 2009 at 16:15
No. Current from the panel is limited by the panel itself. A 30A fuse right at the battery would be good practice.
Cheers,
John
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Follow Up By: guzzi - Wednesday, Dec 16, 2009 at 16:57
Wednesday, Dec 16, 2009 at 16:57
It also sounds like heavier wire is also required to stop the voltage drop. Try some 8mm sq twin core.
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Follow Up By: Member - John and Val - Wednesday, Dec 16, 2009 at 17:33
Wednesday, Dec 16, 2009 at 17:33
No Guzzi. A solar panel is best thought of as a source of current rather than voltage. It's current output remains pretty constant while the voltage is determined mainly by the load. The peak power output occurs when the voltage is about 17-18 volts. Since we don't want more than about 14V at the battery, we can in fact afford to lose those excess volts in the wiring. The better (expensive) controllers actually provide optimum loading so that the panel is operating at it's maximum power point - they use switchmode technology to effectively trade off the excess voltage to increase the current delivered to the battery.
For a simple system, the controller simply disconnects the panel from the battery when the loading provided by the battery is insufficient to hold the panel voltage down (i.e. the battery is fully charged).
It is counter-intuitive to allow losses in the wiring, but in fact, so long as they are not excessive, in this case it is ok.
John
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