Solar charging of the cranking battery ...

Submitted: Wednesday, Jun 10, 2009 at 20:23
ThreadID: 69696 Views:2933 Replies:4 FollowUps:12
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The new Jeep has a cig socket in the back that is always live ..

Could it be used to charge the cranking battery by connecting
a solar panel to it ? Would it cause any problems having 17 volts
passing through it back to the battery ?

I am putting a small solar collector on the roof rack to keep a small

52 aH battery charged in the back of the Jeep - Just thought that by adding another controller / regulator I could put some charge back into the cranking battery ..

Is this a bad thing to do ?

Rgds

Steve
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Reply By: Member - bungarra (WA) - Wednesday, Jun 10, 2009 at 20:29

Wednesday, Jun 10, 2009 at 20:29
would cause significant problems!

all solar panels must be connected through a regulator and then the battery
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Follow Up By: Member - bungarra (WA) - Wednesday, Jun 10, 2009 at 20:32

Wednesday, Jun 10, 2009 at 20:32
I have just re read your post and it is confusing.

You mention you are using a regulator and in the same post state 17 volts back to the battery...might be better if you explained a little clearer what you intended circuits are
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Follow Up By: Mandrake - Wednesday, Jun 10, 2009 at 20:32

Wednesday, Jun 10, 2009 at 20:32
It would be coming through a regulator ( got my voltages crossed ..oops )

So at 14.4 volts max it would be OK ?

Cheers

Steve
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Follow Up By: tim_c - Wednesday, Jun 10, 2009 at 20:36

Wednesday, Jun 10, 2009 at 20:36
Shouldn't be any problem putting 14.4v into your battery - afterall, that's what your alternator does!
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Follow Up By: Peter_n_Margaret - Wednesday, Jun 10, 2009 at 20:43

Wednesday, Jun 10, 2009 at 20:43
Or use a 2 way RedArc and the alternator/crank one end and the aux battery/solar & reg the other.

Cheers,
Peter
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Follow Up By: Member - bungarra (WA) - Wednesday, Jun 10, 2009 at 20:44

Wednesday, Jun 10, 2009 at 20:44
that controlled voltage is not a problem...I would be more concerned how the circuit is wired and protected........subject to how you connect everything the existing is live one way (battery to cig socket in rear...no issue if fused back at the battery for its designed purpose)

add a power source from the other end and it is live from both directions...needs a fuse at rear battery end.......also subject to the amps you draw along it when charging you need to check the wire size suitability..it may overload the cable.

Hard to give a definitive answer without details...but at the end of the day charging a cranking battery from a solar panel even when driving is not an issue in principal...many of us do it...but a dedicated circuit desigend for the expected loads and safety is more sensible.


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Follow Up By: Mandrake - Wednesday, Jun 10, 2009 at 20:55

Wednesday, Jun 10, 2009 at 20:55
Thanks for the info - I need to get some idea on the wiring size - The amps going back would be very low as the panels are only 2 X 15 watts - Just a trickle charge really .
What will be happening when on holiday is -
Fridge connected to Ciggy Plug whilst vehicle is being driven -
Solar panels are connected to Aux Battery .
When vehicle parked plug fridge into Aux battery and plug Solar Reg ( 2nd one )
into the Ciggy plug to keep the cranking battery topped up .

Meanwhile in the camper there is an 80 watt Panel connected to an 85aH Aux Battery which would be used to power lights and fridge on extended stops -

Sounds good to me as long as the sun shines !! If it gets cloudy for more than 3 days I am in deep kaka - because I have no means to charge my Auxiliaries from the Vehicle Alternator --- St George will be a big test for this rig ... 4-5 days without 240 volt power ...

Cheers to all

Steve
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Reply By: Member - Murray R (VIC) - Wednesday, Jun 10, 2009 at 22:31

Wednesday, Jun 10, 2009 at 22:31
Steve
As Bungarra has said your wiring needs to be fused at both ends, the car cig wiring will carry the 2 amp from solar panel but you will probably have voltage drop in wiring which will not give you a high enough voltage to charge the battery. Surggest that you rewire cig plug with 6 mm cable and fuse at both ends to eliminate the voltage drop at the battery

Murray
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Reply By: Member - Mike DID - Wednesday, Jun 10, 2009 at 23:44

Wednesday, Jun 10, 2009 at 23:44
Solar Panels are a constant-current source. This means that for a 2 amp panel charging a car-size battery -

a) They may be 17 volts when open circuit, but will drop when connected connected to a battery.

b) They will still charge the battery at close to the rated current even with wiring resistance.

Go for it . . . .
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Follow Up By: V8 Troopie - Thursday, Jun 11, 2009 at 00:21

Thursday, Jun 11, 2009 at 00:21
Constant current source eh??
Suggest you connect an Ampmeter and watch it as the suns intensity changes. You'll be amazed just how much the charging current changes.

You should add (under b) above:
The 17V solar panel will charge the battery at its rated current IF the battery can accept charging current. That current will drop as the battery reaches its fully charged voltage.
17V from a 15W solar panel into a fully charged car size battery does, in my experience, nothing other than maintaining the battery fully charged. One has to consider here that the car top mounted panel does NOT charge for 24 hours a day.
This arrangement has been maintaining my aux. battery (N7ZZ type) for years without the need of a regulator. For bigger panels, and panels with 36 cells (higher open circuit voltage) a regulator is required.
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Follow Up By: Member - Mike DID - Thursday, Jun 11, 2009 at 07:50

Thursday, Jun 11, 2009 at 07:50
If you connect a Solar Panel that's putting 2 amps into a 12 volt to a 6 volt battery it will still be putting out 6 amps. If you then connect it to a short-circuit, it will still be putting out a little over 2 amps.

Everyone here will be so thankful that you explained to them that it won't be putting out 2 amps in moonlight.
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Follow Up By: oldtrack123 - Thursday, Jun 11, 2009 at 14:55

Thursday, Jun 11, 2009 at 14:55
Hi
I think Mike made a typo
"out 6 amps" should read "out 2amps"
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Follow Up By: Member -Dodger - Thursday, Jun 11, 2009 at 15:07

Thursday, Jun 11, 2009 at 15:07
May I add that a 15watt panel will never be able to generate 2 amps in fact I amp would be nearly it's maximum.
I used to have a handle on life, but it broke.

Cheers Dodg.

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Follow Up By: oldtrack123 - Thursday, Jun 11, 2009 at 15:22

Thursday, Jun 11, 2009 at 15:22
Member -Dodger posted:
May I add that a 15watt panel will never be able to generate 2 amps in fact I amp would be nearly it's maximum..
Hi Dodge
If you reread Mandrakes post he is saying 2x15w panels
If they are 15 w @ 17v so output more like 1.75amps . His 52 amp hr bat would get a slow charge[ around 18hrs of full output]provided no amps drawn from it , not much left to top up the cranker .
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Follow Up By: oldtrack123 - Thursday, Jun 11, 2009 at 15:26

Thursday, Jun 11, 2009 at 15:26
Hi
An error in above post AT 18hrs add from 50% state of charge
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Reply By: Maîneÿ . . .- Monday, Jun 15, 2009 at 19:12

Monday, Jun 15, 2009 at 19:12
Steve,
I use this 140 Amp manual isolator to add/remove the Cranking battery from the solar charging system.
It can also be used to add the two AGM's into the Cranking battery circuit to assist the Cranking battery at any time also.

Image Could Not Be FoundMaîneÿ . . .
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