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13.5 volts not OK. In order to properly charge a car battery, for example, the charging voltage needs to more than this intrinsic voltage of the battery. A car's charge voltage from the generator is 16 - 18 volts which provided electron flow back into the battery. If the rated output of this solar panel is 12 or 13.5 volts, that won't do it.
As a handyman mechanic, I have been working with car batteries and alternators for about 20 years. Also during the last 8 years, I have been installing solar power systems in houses-4 so far. So, in my experience, I have found that car batteries, and deep cycle lead acid batteries can definitely be charged on 13.2 volts and in fact I am doing one right now off a Hard Drive 12 V power pack, putting out 0.2 Amps into my 50 AmpHour battery for my boat. It has been in trickle charge state for 36 hours and is now up to 13.7 volts, having started at 12.4 volts(which means it is only 50% full). When it gets to 14 V, I will turn it off and let it sit for 3 hours and check the voltage. I would like a resting voltage of 12.75 if possible. Batteries in reasonable condition can sit on 13.2 whilst charging at low amps indefinitely, all winter if you want. The problem comes if your charger has no regulation and takes the battery to 14.5 volts and leaves it there. Generally car alternators charge a battery at 14.5 volts and should also drop back to lower voltage after a time (depending on the car, it may only take 15 mins for the alternator to restore full charge after starting). Another feature of batteries, is the Equalising charge which a solar panel array will have built into it in the charge controller. So once a month, the controller will allow the battery pack to be slightly over charged, depending on the type of battery and the charging algorithm. Mine used 15.5 volts for 6 hours, only once a month, and this is intended to stir the electrolyte and reduce sulphation, the big battery killer. As far as I know, car charging doesn't do this. Anything over this is NOT GOOD for starting batteries, not even for fast charging. It is likely to heat the battery, bubble off electrolyte and buckle the plates. Good luck with yours, Roger Levy
I meant it says 12 volt setups and want to know if will work on 24 volt setups
I have a 20 watt panel I believe puts out 1.8 amps. and a controller. can I hook this up to a 24v trolling motor while in dock and get a charge and would I hook up neg post on one positive on other. Some else said this panel and controller would work but it says for 24 volt setups.
I have gone through your blog "How to charge a 12 volt battery using Solar Power" this is such a good topic. I really enjoyed a lot and the blog is really very interesting.
<a href="http://www.electricalgeneratorsltd.com/">Diesel Generators</a>
seconding what the other commenter said: this is a fine tutorial showig how a 12v battery can be boosted, but that or any tiny solar panel is only going to generate 250 ma or so in full sunlight . If you're charging a smallish 12v battery that is 25 ah (=25000ma). Even assuming all of the charge was retained by the battery (usually you need to put an extra 10 -20% in) you're talking 100 hours in the sun. Yes it could trickle/keep topped up, which is a great use for it - but not a normal charge from 'used last week' to 'I want to use it next week'.
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