Can I connect solar panel direct to battery?

Submitted: Sunday, Jan 26, 2003 at 15:59
ThreadID: 3095 Views:22856 Replies:4 FollowUps:6
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Hi All.

I recently purchased a Uni-Solar amphorus silicon 65 Watt solar panel.

This panel is correctly wired into my caravan via regulator voltmetre and fusing to a deep cycle battery so there is no problem there. The fridge in the van is a 3 way and the battery only runs lighting.

The panel however is not permanently attached to the van, this is so that I can walk around with it chasing the sun.

My 4WD has a 2 battery setup. The second battery is a deep cycle and runs the fridge plus all other non vehicle essentials.

We have here a situation where the caravan gets more that enough power and the second battery in the 4WD runs down quicker that I would like it to as it runs an early model 39 litre Engel.

I do not want to install a regulator for a solar panel hookup to the 4WD if I can get away with it.

My question. Can I connect the solar panel (rated 65 watts) direct to the second battery with just alligator clips without a regulator in an attempt to prolong the charge of the battery I am told that the solar panel is fitted with a blocking diode.

I know that I can always keep swapping the 2 deep cycle batteries every 2 days or so, but the damn things are also very heavy.

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Reply By: Darrin - Sunday, Jan 26, 2003 at 16:05

Sunday, Jan 26, 2003 at 16:05
yes you can connect without using a regulator.You just have to watch that you dont overcharge your battery.This seems very unlikely as your panel would only put out about 5 amps at best and your fridge and other possible load would exceed that.
AnswerID: 11878

Reply By: Janset - Sunday, Jan 26, 2003 at 16:23

Sunday, Jan 26, 2003 at 16:23
Thank you.

That is what I thought, but it never hurts to ask.

AnswerID: 11879

Follow Up By: Oziexplorer - Sunday, Jan 26, 2003 at 16:47

Sunday, Jan 26, 2003 at 16:47
Janset I would recommed from Jaycar
an XC0116 that will allow you to monitor your fridge tempreture to ensure it is not to warm or to cold, as well as the voltage of the battery.
These are $39.95

It is preferable to use a small polarised plug and socket for your caravan and for your car to hook up your solar panel. Clips are natorious for causing problems. Your local Jaycar or Dick Smith store has quite inexpensive polarised inline plugs and sockets which will more than capably handle the power from your solar panel.
FollowupID: 6789

Reply By: joc45 - Sunday, Jan 26, 2003 at 16:48

Sunday, Jan 26, 2003 at 16:48
yes, you can, but risky - you will need to watch it that the battery doesn't exceed 15v. This is about the upper limit of the earlier Engel, incidentally.
Do you have a spare pin on your trailer socket? Why not run a lead, using tht pin, between your caravan battery and your 4wd aux battery, thus ensuring that both are fully charged, and thru a common regulator. This also means that the 4wd gets to charge the caravan battery when travelling. If the 4wd is detached from the caravan, precluding the above, why not make a long lead with plugs which can connect the caravan up to the 4wd, parallelling the two batteries.
AnswerID: 11882

Follow Up By: Oziexplorer - Sunday, Jan 26, 2003 at 17:37

Sunday, Jan 26, 2003 at 17:37
For the size of the cable you need to do as you suggest, would need more than one pin of the trailer plug to handle the size cable required.

Trying to charge two auxilliary batteries especially with the other one being so far away would not be a good idea or really practical. You would have to use approximately 10mm cable to go that length, and preferably oxygen free copper, and switch the first auxilliary battery out of the circuit. Rotary switches for that are easily obtainable.

With an Engel connected 24 hours to an auxilliary battery at between 4C and 6C, there is no chance at all of overcharging the battery from a 64w solar panel.
FollowupID: 6792

Follow Up By: Joc45 - Monday, Jan 27, 2003 at 20:05

Monday, Jan 27, 2003 at 20:05
10mm cable? We're only charging batteries here, not cranking diesels. Any voltage drop due to a small cable will only limit the charge current, and as the van battery reaches full charge, the voltage drop will reduce to a minimum.
Re oxygen-free cable, I thought only hi-fi audiophiles with excess cash problems bought that stuff. Copper manufacturers suggest that it makes virtually no difference to the conductivity of the cable, just that it has a guaranteed minimum of CuO. Audiophiles suggest that the CuO may contribute to some non-linearity in the resistance of the cable, causing minute audio distortion, but I don't think your battery will notice the difference in the music quality as it happily charges on the cheaper standard-grade copper.
(have I just started a new forum on OF copper cable?)
FollowupID: 6829

Follow Up By: Oziexplorer - Monday, Jan 27, 2003 at 21:19

Monday, Jan 27, 2003 at 21:19
Joc, oxygen free cable is most definitely not just for audiophiles. Oxygen free cable offers substantial benifits and is being used widly today in industry and the motor vehicle sector. The benifits of oxygen free cable are higher electrical and thermal conductivity, is less brittle and more flexible and less subject to failure. Shortly, oxygen free cable will be the only cable you will buy. A large percentage of the industrial cable in the automotive and transport industry is already oxygen free, and will continue to rise daily. In many applications today, oxygen free cable is mandatory to be used. Oxygen free cable now is the same price as the non-oxygen free product, so why accept second rate product if you consider your money to be first class.

Before I answer the rest of your statement, what do you think of this below:
These are the recomended cable sizes for connection of a compressor fridge and battery. (Danfoss BD35, BD50, SawaFuji)
12V operation For 24v operation you can double the distance.
Distance from battery.___ Cable Cross-section mm2
2.5mts________________ 2.5
6.0mts________________ 6.0
10.0mts_______________ 10.0
FollowupID: 6839

Follow Up By: Goodsy - Monday, Jan 27, 2003 at 21:26

Monday, Jan 27, 2003 at 21:26
Not true Joc45. 10mm sq is the minimum I would run to charge the main battery. The voltage from the solar panel is limited to around 13.6v. Having the van battery fully charged does not vary this. 13.6v at van approx 14 meters (got to take into acount pos and neg) of 2mm sq cable through van plug from regulator to main battery, volt drop probable around 1 volt. You will not charge a lead acid battery with 12.6 volts. If you ran 10mmsq (I have 25mmsq) volt drop would be a lot less about 20% of the 2mmsq cable thus charging the battery. Cable bigger the better when working with extra low voltage.
FollowupID: 6840

Reply By: Janset - Sunday, Jan 26, 2003 at 18:04

Sunday, Jan 26, 2003 at 18:04
Thanks guys. A lot of good info here and all welcome.

AnswerID: 11884

Follow Up By: Peter S - Tuesday, Jan 28, 2003 at 08:08

Tuesday, Jan 28, 2003 at 08:08
Just as a quick suggestion
The cables running from the solar regulator to battery cut these and put in a 32v socket. Then mount a 32v plug and connect battery leads to this.
Make up a lead with the largest twin lead you can get from solar shop (Maybe the same size cable used in lead from solar panel to reg) with plug on one end and Gater clips on the other to connect to car battery.

When you want to charge van plug into van socket and charge the car,plug into car socket.
Also to keep cable from regulator to battey in car short just drive the car to nearest point of regulator

Personally I would not charge without using a regulator.

There may be some loss of Voltage but tis enough to keep you going for a long while

FollowupID: 6856

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