Emergency battery charging from solar

Submitted: Sunday, Oct 04, 2015 at 13:51
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We found ourselves with a flat battery at a bush campsite the other day and were lucky to have other campers around to run jumper leads to the battery. If we were alone can I connect my 50W / 2.37A solar panel direct to a flat battery and get enough charge into it to start the car

Thanks
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Reply By: Hoyks - Sunday, Oct 04, 2015 at 14:22

Sunday, Oct 04, 2015 at 14:22
As long as the panel is regulated, and at 2 amp, you might be there for some time.

Be careful though as to the voltage the panel is spitting out. I bought one from Aldi and the regulator on that is supplying 18V at 10 Amp, which won't so you battery a lot of favors if used long term.

If your battery has dropped a cell, then charging won't bring it back either.

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Follow Up By: Wandering Wallys - Sunday, Oct 04, 2015 at 14:28

Sunday, Oct 04, 2015 at 14:28
Thanks Hoyks

Panel is unregulated ~ Max voltage is stated as 21V so I assume I will need to add an in-line regulator (or get a different panel)
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Follow Up By: Nomadic Navara - Sunday, Oct 04, 2015 at 15:04

Sunday, Oct 04, 2015 at 15:04
With such a small charge current a regulator would get in the road. It will take some time to get the battery voltage up to any reasonable level for a motor start. Monitor the battery voltage until it is over 14 V before attempting a start.

There is no problem connecting a panel to a battery if you are monitoring it, after all a PWM regulator when used with a panel that small just looks like a short circuit until the battery terminal comes up to the absorption voltage. The main thing is to monitor the voltage rise of the battery and remove the charge if it goes up over 14.5 V. The only time you need a regulator is if you are going to leave the system without having someone there to monitor the charging.

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Reply By: Roachie.kadina.sa.au - Sunday, Oct 04, 2015 at 14:24

Sunday, Oct 04, 2015 at 14:24
Yes, but it will take a loonnnnngggggg time to get enough charge into the battery.

Of course it depends on a couple of things....how flat is the battery to start with? What type/size engine are you trying to start? (a large 6/8 cylinder diesel engine needs a helluva lot more amps than a little 4 cylinder petrol engine to crank/start).

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Reply By: Frank P (NSW) - Sunday, Oct 04, 2015 at 14:27

Sunday, Oct 04, 2015 at 14:27
WW,

Yes. Depending on the obvious, like how discharged your battery was and how much sun there is, it could take a while to get it to cranking voltage. Also depends if the car is an easy starter. But certainly do-able, even if it means an extra day's camping :-)
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Follow Up By: Frank P (NSW) - Sunday, Oct 04, 2015 at 14:30

Sunday, Oct 04, 2015 at 14:30
Just to add a bit more - the panel is small enough to not damage the battery while doing what you want. I wouldn't leave it on long term without a regulator.
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Reply By: garrycol - Sunday, Oct 04, 2015 at 14:40

Sunday, Oct 04, 2015 at 14:40
The voltage is not enough to damage the battery if connected for a short period - but do not leave it on for a long period as it will damage the battery.

You do not need to fully charge the battery - just get enough in to start and then let the alternator do the rest of the charger.

So in full sun - my guess is about 30 min on charge will not damage the battery but provide enough to start.
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Follow Up By: Zippo - Sunday, Oct 04, 2015 at 17:20

Sunday, Oct 04, 2015 at 17:20
30 minutes? That won't even put 1.5Ah back in ....
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Reply By: Nomadic Navara - Sunday, Oct 04, 2015 at 14:48

Sunday, Oct 04, 2015 at 14:48
A couple of amps is not much charge. If you connect the panel without using the regulator you may get a start by mid day and have a good chance or a start bu 3.00 PM.


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Reply By: Iza B - Sunday, Oct 04, 2015 at 14:51

Sunday, Oct 04, 2015 at 14:51
Simply connect raw panel output to the battery and wait, maybe for several hours, maybe days. A couple of potential amps from a panel in direct sun will take a long time to lift a flat battery to a usable condition. Disconnect the battery from the vehicle wiring before connecting the panel to the battery.

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Reply By: HKB Electronics - Sunday, Oct 04, 2015 at 16:32

Sunday, Oct 04, 2015 at 16:32
It depends on a few factors, is the battery healthy, how low have yopu discharged it, what
are you trying to start.

I have had small 4 cylinder cars start after charging for 10 minutes or so with a 5A charger, a V* diesel would be another matter.

Generally if you can bring the surface charge up with a 10 mimute charge you will probably get the motor to turn over a few times, if you lucky and the car starts easily then this might get you going.

If its a diesel you you have to power the glow lpugs etc, as long as the cars and battery a in good condition I would be surprised if you couldn't get it to fire up with two to three hours charging of a 2A panel. Of course I'm assuming you have all accessories off and quickly start it.

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Follow Up By: garrycol - Sunday, Oct 04, 2015 at 16:50

Sunday, Oct 04, 2015 at 16:50
I have a V6 diesel and occasionally I forget to switch off my cubby fridge and the battery is flat the next day. I also have a 900CCA Supercheap battery power pack that does not have enough oomph to start my engine but if I leave it connected to my car battery for about 10 mins there is enough transfer of power to the starter battery to start - but my car normally starts first go and you only get one or maybe 2 starts - or only one if glow plugs are required.

If no start then wait another 10 mins.

Is really similar to those little jump starters that plug into the system via the cig lighter or preferably direct to the battery.
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Reply By: Member - John and Val - Sunday, Oct 04, 2015 at 20:29

Sunday, Oct 04, 2015 at 20:29
It was dark and stormy with night rapidly approaching and the rain setting in. Wipers on and Troopy’s big petrol engine ( with electric ignition) just about stopped! Quick measure the battery voltage – the alternator had died just 200 km from home at the end of a 20000km trip.
We struggled into a bush camp we knew a few km away, no lights, no wipers but our luck held. Then we even found an unoccupied picnic shelter before turning off the engine for maybe the last time.

Troopy carries solar panels on top and 200 Ah of aux batteries which by now were virtually empty, having taken over much of the heavy lifting. A bit of rewiring so all batteries were in parallel and fed by the panels. The following morning Troopy came to life and we slowly drove through fog for an hour or more before reaching sunlight. What a joy to see amps going into the batteries! I’ve no doubt that ours is the only solar powered Troopy ever.

As others have said, in your situation, just connect your panels to the starting battery and wait. I’d recommend any traveller going bush carry a multimeter. Watch your battery voltage as charging proceeds – it should eventually (after some days with your panels) reach around 14.4 volts and the panels should then be disconnected. The battery is probably sufficiently charged to be useful when it’s risen to well over 13V, say 13.5V. Again as already said it depends on battery condition, engine size and type, temperature, etc etc.

Cheers

John

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Reply By: Les - PK Ranger - Sunday, Oct 04, 2015 at 23:23

Sunday, Oct 04, 2015 at 23:23
If you are wanting to upgrade your panel to something that is a little different, and handy, consider a folding blanket type panel (though nowhere near the cost of a proper amorphous type !).

I got one of these from Supercheap . . . Ridge Ryder folding Solar panel 100w
Has everything built in, I just face car to the sun, unfold across the windscreen (blocks sun from cab and gives good sun angle), and hook up, 2 mins flat and charging in full sun at just over 6amp/hrs.

Wait for 20% off sale and bag it for $319.20 like I did :)
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Reply By: Bob Y. - Qld - Monday, Oct 05, 2015 at 09:56

Monday, Oct 05, 2015 at 09:56
Others have suggested bypassing the regulator in your situation and I'd agree, Wally.

For close to 20 years, we ran a 36W panel into a N70 battery direct, without any real dramas. The battery was used to power a Barrett HF radio and a UHF, mainly during daylight hours. Once we got the phone on, in '92, the HF was eventually "pensioned off", and only the UHF used.

Rarely had flat batteries, and the batteries lasted about 2-3 years, which was more than we were getting out of them in the station Landcruisers.

Bob


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