240v charger and solar regulator

Submitted: Monday, Apr 25, 2011 at 07:34
ThreadID: 85844 Views:5644 Replies:1 FollowUps:8
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I have a 12V/10A solar regulator with a 10W solar panel. This panel is insufficient to charge the 70AH battery in one day. I would like to add a 240V 20A 3 stage charger so that the battery will charge when we are in a powered site. Does anyone know if it is safe to connect the charger to the battery without damaging the regulator?
I have a 240/12V fridge (no gas :-( ) and want to use the battery to keep the fridge running while we are on the road.

Alternatively, what precautions should I take if I connect the 12v supply for the fridge to the cars electrical system?
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Reply By: Member - John and Val - Monday, Apr 25, 2011 at 08:17

Monday, Apr 25, 2011 at 08:17
Lester,

Hope that your "10W" is a typo! Did you mean 100W or more??

If it is only 10W, it's only possible use is to keep the battery alive when it's not in use for extended periods. You will need at least 100W, preferably 120W or more to handle a compressor fridge such as Engel or Waeko.

Can you run a mains charger while the panel regulator is connected? - Yes, you will not damage the regulator, but if you have a decent sized solar panel in the sun it may interfere with the charger's multistage operation. No downside though.

The fridge - Is it a 3 way fridge (240V / 12V / gas) but you don't carry gas, or is it only 12V/240V?? If it is capable of running on gas, forget trying to run it off a battery; it is far too power hungry for a battery. If it is a compressor type, (if not sure - tell us the make and model) then a 70 Ah battery should handle it for at least a day.

To connect to the vehicle - depends on the type of fridge - if the fridge is capable of gas operation the vehicle alternator can keep the fridge cool while the engine is running, but must be disconnected (reliably and preferably automatically) when the engine is not running. (A non-compressor fridge draws a continuous 12-15 amps, that's more than your headlamps, and will flatten a battery in a few hours to a point where it wont start the engine.) A compressor fridge could probably run safely overnight from the vehicle battery, but I wouldn't stretch it much further.

You can charge the second battery from the vehicle but must have an isolator to ensure it is disconnected when the engine isn't running. You must use heavy cable to avoid losses, and unless it is a compressor fridge, the fridge should not share the charging cable.

Suggest check out our blog Electricity for Camping. It includes a lot of stuff I think you'll find useful.

Cheers

John
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AnswerID: 452228

Follow Up By: lesterb - Monday, Apr 25, 2011 at 09:27

Monday, Apr 25, 2011 at 09:27
Thanks for that info John.
The solar panel is only 10W not type. I have just been using it at home where it is connected for weeks between trips to trickle charge the battery.
The fridge is a 240/12v only (no gas).
We usually stay in parks on a powered site or use a sine wave generator when not in a park. All I want to do is keep the fridge cool while we are travelling, 8 - 10 hours maximum.
What do you recommend to automatically disconnect the supply from the car when the engine is not running or is it OK to leave it connected for short pit stops?

I've had a read of your very good blog covering power for camping. The section on 240v volt chargers raised one question. If different types of batteries require different constant voltages, how is this maintained as most chargers I've seen don't have selection for different output voltages?

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Follow Up By: Member - John and Val - Monday, Apr 25, 2011 at 10:25

Monday, Apr 25, 2011 at 10:25
Hi Lester,

A 10W solar panel is ideal for your present use, trickling into a battery for long term storage. It will deliver up to about 0.6 amps, so on a good 7 sunshine hours day maybe 4 amphours. I would expect any compressor style fridge to draw about 3 to 5 amps when running, and to run for about 1/3 of the time - that's 20 to 30 amphours drain per day, far more than the 10W panel can help with.

If you are able to charge your battery from 240V each day, maybe a a good sized battery alone is all you need to run the fridge.

To charge it from the vehicle will involve installing in the vehicle some controller to connect it to the vehicle battery when the engine is running. This could be a dual battery controller (talk to member ABR sidewinder, ARB or similar suppliers and expect to pay $100+) or a simple system with a relay (I use headlight relays for this sort of thing) controlled by a switch, or just wired to your accessories circuit so that it operates with the ignition key in the accessories position. For short pit stops I'd leave the fridge running, but not for extended periods like overnight.

Chargers - the better multistage chargers have provision to select for different types of batteries. Most chargers will do (at least) a fair job, but for a good job, the charger should be matched to the battery type. I hope Peter (Member Battery Value) or someone with similar depth of expertise will pick this one up. It is important when we aim for maximum energy storage and my experience is too limited to be helpful.

Cheers

John
J and V
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Follow Up By: lesterb - Monday, Apr 25, 2011 at 10:35

Monday, Apr 25, 2011 at 10:35
Thanks again John.
I've learnt a lot about batteries and chargers of the past couple of hours thanks to you.

Lester
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Follow Up By: lesterb - Monday, Apr 25, 2011 at 10:40

Monday, Apr 25, 2011 at 10:40
I just thought of another possibility. My car has a cigarette lighter auxilliary in the back, I presume in parallel with the one in the centre console. As my fridge draws approx 5A would it be acceptable to extend this to the fridge in the caravan via Anderson plugs and a 10A fuse for safety? I guess the socket in the back is meant to power Waeco and similar fridges when travelling.

Lester
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Follow Up By: Member - John and Val - Monday, Apr 25, 2011 at 11:05

Monday, Apr 25, 2011 at 11:05
Lester,

Assuming that the fridge is in fact a compressor type (that is yet to be positively established) -

I'd certainly try using that rear cigarette lighter socket, though it's likely to be marginal. First I'd check that it is in fact turned off unless the ignition key is in the accessories position (same as the one in the dash). If it is, then go for it.

Why marginal? There are voltage losses in any wiring and while the losses may be acceptable for a fridge in the back of of the vehicle, extending beyond that and out to the van may be pushing your luck too far. Secondly - a cigarette socket is pretty unreliable for fridge use; the plug can work its way out to provide a poor connection which heats up and the connection deteriorates further, getting hotter, deteriorating, etc..... Suggest try it and if it looks promising, provide a heavy twin cable connected to the back of that socket through an Anderson plug to the van, thus bypassing the socket itself. (It is important to disconnect the battery while working behind the socket.)

Generally, I believe in fitting fuses at every energy source. There will already be a fuse protecting the wiring to that rear socket however, so it is not essential to fit an extra one.

Final thought - that socket is a very useful place to plug in a worklight. A LED (or other) light fitted with a cigarette lighter plug would be useful around the vehicle and also provide an easy way of checking where power is (or isn't!)

Cheers

John
J and V
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Follow Up By: Battery Value Pty Ltd - Monday, Apr 25, 2011 at 11:17

Monday, Apr 25, 2011 at 11:17
Hi John and Lester,

as always, good explanations by John..

Lester, I've found the difference in charging voltages aren't too much of a concern between different types of batteries.
If you select a charger which has a setting for 14.4V in absorption and 13.6~13.8V in float, you're all set.
Problems can occur if the charger doesn't switch back to float after absorption due to concurrent fridge operation, or if the charger is too small for the battery.
This may lead to some over-charging and faster than necessary battery ageing.
In a well designed charger the output voltage has some 'softness' to it.
This causes the voltage to sag to somewhere between absorption and float level while the fridge compressor is running, reducing the over-charging current throught the battery somewhat. The moment the compressor cycles off, a good charger will immediately revert back to float (if the battery's almost fully charged).

Best regards, Peter
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Follow Up By: lesterb - Monday, Apr 25, 2011 at 11:30

Monday, Apr 25, 2011 at 11:30
Thanks John and Peter,

Just to clarify, the fridge is a compressor type and I was planning on connecting to the wiring behind the rear socket not connecting via a plug.
If I do this there will be no need to connect the fridge to the battery in the caravan and I can use it purely as a standby for LED lighting and the 12v LCD TV when not in a powered site and the generator is not running.

Lester

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Follow Up By: geocacher (djcache) - Tuesday, Apr 26, 2011 at 23:40

Tuesday, Apr 26, 2011 at 23:40
Generally the factory wiring to accessory plugs isn't much good at 5 amps. It's tiny and the voltage drop affects the fridges efficiency even though it will actually run.

You could help here by providing brand and model. Different situations exist even in compressor fridges. Eg engel no low voltage cutout vs Waeco & ARB with cutouts. Sometimes the cutouts are adjustable, sometimes not.

Expect to use 5mm-6mm cable of a reputable brand to a dedicated fridge socket over a vehicle length. Bigger diameter again for your proposed run all the way to the trailer via Anderson plugs.

Dave
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