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Portable dual battery system

1K views 3 replies 4 participants last post by  ornea 
#1 ·
Hey guys,

I do a lot of travelling for work and want to bring the fridge along with me. Only problem is that I use a company car and cant install a fixed setup.

I was thinking is it safe to connect a second battery into the cigarette lighter?

I understand that its only supplied by small wires and probably fused at 10 or 15A.

How much current does a charging battery produce?
What voltage comes out of the cig socket? 12v or 14v?

Fridge is an Engel eclipse 38L
Battery is a Supercharge allrounder 105AH

It would only be powering the fridge and nothing else. Or all this wishful thinking?

Any advise and/or ideas would be greatly appreciated.
 
#3 ·
Assuming your 12V fridge is at the back of the car, getting a battery box as advised above is the solution.
I'm guessing you wanted to connect the second battery to the cigarette lighter socket to charge the second battery? Obviously a bad idea as the cigarette lighter socket is not equipped to handle possible high amp draws through it to charge a possible low charged second battery. If you're to charge your second battery using the alternator of the company car, then you're looking at installing a dual battery isolator relay unit or a manual switch to separate the two batteries when the second battery is being used.
Some kind of tampering and wiring will be necessary to charge your second battery using the company car's alternator, whether it's temporary or permanent.
 
#4 · (Edited)
How much current does a charging battery produce?

More correctly, How much current does a charging battery draw? The amount of current that a Lead Acid battery draws is determined by:
1. the state of charge, (less charge, greater demand)
2. the capacity of the battery (Amp Hour or CCA. A small motorcycle battery will draw less than a truck battery, all other things being equal )
3. the supply voltage of the charging circuit
4. the ability of the charging circuit to delivery the current demanded. (The following are my views and the reality may differ significantly. Ideally a charging system should be able to delivery C/5. A typical patrol battery will be around 90Ah so approx 18Amp (i.e. 90/5 )charge current. However, vehicle manufactures may need to trade off charge time against optimal charge rate. i.e. Many trips may be short so they need to try to charge as much as possible in that time so provide max charge currents significantly higher.)

As others have stated and as you suspect the charging demand of the battery may exceed the limit of the cigarette lighter and unfortunately not the best charging source.

What voltage comes out of the cig socket? 12v or 14v? The cig socket voltage is basically directly connected to the battery once the acc is on (most cars). So if you were to measure the voltage when the ACC is first turned on you would see about 12.4 - 12.8 volts. As the engine is cranked it will drop perhaps as low as 10.5v. Once started the charging circuit will try to boost charge the battery until it reaches 14.4v, which it will sustain for a period of time, then it will back off and sustain a float charge voltage of 13.8v. These voltages will be seen at the cig socket (with nothing connected)

The voltages above are all dependant on battery and charging circuit health and is also a simplification but should give you a general idea.
 
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