Hi,

 

I just wanted to double check if there's any reason I couldn't charge a battery through a cigerette lighter from my second car while I'm driving? I'm looking at just rigging up a cigerette plug to 2 crocodile clips and have them clipped onto the battery. Would that be ok?

 

Vijay

Your require a charge splitter like when you have a caravan, reason is the alternator output is regulated by the battery charge level, and the vehicle power use, if for instance you were driving using next to no electrical power and the car battery was fully charged the second battery plugged into the cigerette socket would cause the alternator output to rise which is great for the flat battery but not so for the fully charged car battery.

 

To be fair it is a bit more complicated than that but in simple terms what you have suggested without a charge splitter will interfere with the charging systems. Get along to your local caravan parts supplier they will have what you need.

 

Jeff TT

Hi Jeff,

 

Done a quick search and found this - http://wiki.80-90.co.uk/index.php/Camping_Interior_Fitting_a_split_charger

 

I should mention that I don't intend to leave the battery connected to the cig lighter. I need a 12v supply for something else so just wanted to hook it up to charge while I'm driving. Does that make any difference?

 

Also my 4 x 4 already has 2 batteries connected in parallel.

 

Looked at some caravan parts places online and can't see anything like charging splitters :(

 

Vijay

Edited January 10, 200917 yr by vijay

Here you are Vijay this is exactly what you want.

 

http://cgi.ebay.co.uk/12V-SELF-SWITCHING-SPLIT-CHARGER,-CHARGE-SECOND-BATTERY_W0QQitemZ110334704131QQcmdZViewItemQQimsxZ20090107?IMSfp=TL090107131001r24468

 

The relay method you mentioned is not really suitable for electronic sensing as the zed alternator is.

 

 

Jeff TT

Thanks Jeff. Should have mentioned it's not in my Z, it'll be in my Mitshi Challenger (Shogun Sport).

 

So in you're opinion there's no safe way to just charge a battery throught the cig lighter while driving the car?

So in you're opinion there's no safe way to just charge a battery throught the cig lighter while driving the car?

 

Its not really all about it been unsafe, just not the best way to do it, also and this is more important from a safety point of view, is having an insecure battery in the cabin or boot is a no, no, gassing , open terminals and in the event of an accident a potential hazard from acid splashing, electrical shorting ( fire) and a bloody heavy missile.

 

Sorry mate not trying to disrespect your idea, it would work in the short term, but safety has oddly become a major factor in my life of recent years, something about getting older I expect, can not remember been so safety concious in my 20`s.:rofl:

 

Jeff TT

lol, I'm the same mate. I recently starting making my own biodiesel and my middle name is safety :D

 

I was just looking of a real easy way of topping up a spare battery without keeping it plugged into the mains. I've got a cig socket in the boot and the battery would not be able to move about. It'd also be unplugged when I parked up.

 

I'll have to rethink it :)

Sorry Jeff but i've got to disagree with you on this one. My other car's a camper van and i've spent many many months researching split charge systems (you'll find a post of mine on the Club 80-90 wiki under "Heavy duty charging").

 

The regulator on the alternator holds the voltage output at 14.4v regardless of the load and is set at that voltage cause that's over the fully charged open circuit voltage of a battery enough to charge it quickly but not high enough to damage it. If you flatten the battery a bit before you start the engine then the open circuit battery voltage will drop and so when you start the engine they'll be a bigger difference between the alternator output and the battery voltage. This voltage or potential difference is what causes current to flow from the alternator to the battery to replenish the charge.

 

If you have a fully charged battery connected to a running engine and you suddenly connect a battery that's only half charged then the current output of the alternator will rise but the entire amount that it's risen will go to the second battery. The amount going to the engine battery won't change at all because it's open circuit voltage won't have changed. Only issue is if you connect a dead or damaged battery the current going to it would exceed the max current output of the alternator and then the voltage would drop enough so the duff battery would steal some charge from the engine battery.

 

The ebay item that you linked to would be the same as connecting the battery to the cigarette lighter socket, but would do it automatically instead of having to physically plug it in. How that works is, it is just a voltage switched relay and when it senses the voltage rise above 14v it assumes that the engine is running the alternator as battery voltage wouldn't get that high on it's own. When it switches it connects the second battery to the engine battery so both are charged at the same time. (These relays don't really work though. Just check on the Club 80-90 forum and you'll see the trouble people have with them).

 

All that being said, connecting a second battery to the cig socket has some problems. The cig socket fuses are normally rated at 15A so if the battery is under about 2/3 charged there's a good chance you'll blow the fuse. Also if the battery isn't a sealed type it could give off gases when being charged which isn't great inside the car.

 

If it's something that's really important to you the best way to do it is run a fused bit of decent sized cable from the +ve terminal on the battery through a split charge relay as shown in the Club 80-90 link and from there to where the battery will be charged.

 

This is the second post in a row where i've contradicted what someone has said but i hope you don't think i'm trying to start an argument. It's just this is the first time when i've felt i've known a bit about a subject that's come up.

 

Dave