Can I Extend Car Battery Charger Output Cable

[Contax]

I don't like mains wires stretching across drive unattended so instead of putting car battery charger under bonnet I was thinking of extending the 12v output leads to 10 mtr so charger in house just 12v running outside.
Would I lose any output voltage due to longer output cable or would it still charge battery ok.
I would be useing orange 2 core mains cable as used to power electric lawn mowers.

 

[MikeHalloran]

If it's for charging an electric car, think welding cable.
I.e., at high currents, you need fat wires to keep the voltage drop reasonable.

If it's for charging the battery of a fueled car, you still need moderately large cable, unless the charger has remote sense terminals.



Mike Halloran
Pembroke Pines, FL, USA

 

[Contax]

It is for charging car battery, maximum 6amp charger may even use my 3.6amp electronic charger I have, the orange cable I was going to use is same as used for mains B&D lawn mower, it looks thicker cores than that fitted to charger, I was concerned about voltage drop over length of cable if any. It's only to top up battery in cold snaps as car often stood 2 weeks and goes a bit low, had it tested and good battery, cold and BSI computer circuits tend to drain it a bit.

 

[IRstuff]

It shouldn't be a big problem, but your charging time will increase somewhat. During the initial charging the IR drop will eat into the charging voltage, but eventually, the battery voltage will get large enough that the current goes down, and the IR drop will become negligible.

However, you battery oughtn't be losing charge that quickly. You might want to check if there is a parasitic load that's draining your battery. If there is, you might want to add a kill switch to that particular load.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[Contax]

Thanks IRstuff, by IR drop I think you may mean resistance could make my 6amp charger work like a 3 or 4 amp which would be fine as steady charge is better, when battery won't operate starter solenoid it wipes out BSI computer settings, my little LED readout tester shows 12.5v and I took battery to be changed for a new HD one but garage said still good battery and common fault with modern cars stood for 2 of 3 weeks, cold snap and the(Parasite)BSI computer drains enough to take peak out of battery, I only use car at night when using lights, air con & heater fan for 5 mile trip to supermarket so it does not get chance for alternator to fully put back charge used, only way to switch off BSI is disconect battery each time then have to reset everything when I have reconnected battery. I remember a Dr friend years ago who had a new Ford RS, every time he left it for 2 weeks at airport when on holiday he had to get AA to come and start it on return as alarm drained battery. Years ago I had a car with a battery charger (bit like old ignition coil) fitted under bonnet always connected to car electrics just plugged plugged mains lead into it when I wanted to top up charge, dont see them any more (but must not charge battery while connected as can damage expensive BSI computer),I can start it with battery booster pack but need wife to hold booster while I start it, then it goes first touch, oh how I would like a simple car again.
I will make a lead up and try in next time it fails to start as garage says it will still happen with a new battery so better to be prepared.

 

[evelrod]

Remote located battery chargers, so called "float chargers" are commonly found in motor homes. Mine is located 27' from the batteries and is wired in with 10 gauge wire. Seems to work just fine. Observed charging rate seems in the 10amp range most of the time for three 12v 850 amp/hr batteries in parallel.

I'm pretty sure you would need a pretty big set of cables if your trying to "boost" a dead batter to start...That and a high amp charger.

Rod

 

[Contax]

Thanks evelrod, I am not trying to use as a booster to try and start the car. The battery becomes slightly discharged when stood in cold period for couple of weeks of no use and the BSI computer is draining a little power all the time, I just give battery a top up charge with 3.6amp or 6amp charger and everthing is fine, I am just extending the wire from charger to battery so charger is inside house and only 12v cable going across drive outside, much safer than mains cable across drive with charger laid under bonnet overnight. I see yours is doing same thing but heavier current and cables on bigger batteries, I will be using twin core double insulated mains cable for the extended 12v run which is thicker cores than original output cables on charger, going by what IRstuff explains I expect battery may be charged at slightly lower rate than charger ouput due to resistance of longer output wire, battery is onlt about 45ah so if it received half the output of 6amp charger it would be plenty over 24 hours to top up battery as not fully discharged, charger will be disconnected and battery reconnected to car before starting car, I know to start car with charger connected I would need a heavy duty starter type charger with heavy jump leads to battery as used in garages, I do not have much faith in cheap home starter chargers which would only do the same job as my 12v booster battery pack, start the car but not top up battery for future starting.

 

[IRstuff]

Most chargers, such as you describe, with onlu a few ampw output would completely unable to even engage the starter relay, much less crank the starter motor. A typical starter motor load might be something on the order of 80 amps. Even the typical jumper cables might be too large a resistance sometimes.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[theoldwizard1]

I agree with MikeHalloran

"If it's for charging the battery of a fueled car, you still need moderately large cable, unless the charger has remote sense terminals."

I don't have access to any wire gauge voltage drop charts but think 6 gauge or larger for a distance of 10 meters !

I worked for a major automotive manufacturer in engineering. Frequently we had test vehicles with equipment that needed to be run in the field even when the engine was off. The standard vehicle battery had inadequate capacity so an additional battery was wired in the trunk (boot). Even with 12 gauge wire, the voltage available at the rear battery was not sufficient to completely charge the battery.

Of course modern charging systems (i.e. voltage regulator) are much more "conservative". Old vehicle voltage regulators would allow 15+ volts if the battery was in a very low "state of charge".

 

[IRstuff]

"Even with 12 gauge wire, the voltage available at the rear battery was not sufficient to completely charge the battery"

Well, just on the face of it, it had nothing to do with the wire gauge, since the IR drop of 24 ft of 12 gauge wire at 6 amps is only 0.23V. The bottom line is that taking a fully charged battery and hooking it up to a discharged battery leaves you with two partially discharged batteries.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[evelrod]

Keeping with the OP on this...Went to start my Dodge/Cummins a few days ago, it sits for far too long these days. Dead batt. Well, at least dead enough it would not kick over that big diesel.
My solution was to buy a small solar battery charger and plug into the cigarette lighter. Just lay the solar panel on the dash and let the sun (lots of sun in Socal) keep up with the alarm system/radio/clock display drainage.
We'll see how it works out in a few weeks.

Of course modern charging systems (i.e. voltage regulator) are much more "conservative". Old vehicle voltage regulators would allow 15+ volts if the battery was in a very low "state of charge".

Just FYI...The initial startup charge on the Dodge was 14.95v for several minutes and commonly charges at 13.9v.
The Chebby 454 in the motor home hits ~15v if any of the three batts are down significantly.
I've been at this a while and except for the NASCAR stuff we watched several years back (normal charge ~20v on an 18v battery), the charging rates on new cars are much unchanged in about 60 years. The limiting factor is the lead/acid battery technology. Perhaps we will see changes in the next few years since the first lithium-ion batteries are showing up in some 2011 imported cars.

Rod

 

[waross]

Do you remember when 13.8 was almost gospel for charging 12 Volt batteries, Rod? Almost from the start of the change from generators to alternators. Like you I am now seeing higher voltages, 14 and up to 15 Volts. Actually, the alternator supplies as much current as it is able to try to drive the battery up to the set voltage. When the battery voltage reaches 13.8, 14.95, 15 or whatever the set point is, the current to the battery drops to almost zero and the alternator produces enough current to maintain the accessories and other loads at the set voltage.
Note that the regulator does the job of maintaining the voltage at the set level very well. However depending on where your voltage monitoring circuit is connected there may be a small difference between indicated voltage and the voltage at the regulator sense terminal.



Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[thruthefence]

Here's a DC wiring reference, from an old FAA advisory circular dealing with voltage drops and wire sizing.

scroll down to pg 21 of the PDF file.

http://lotus-europa.com/manuals/misc/aircraft_manual/Chapter 11.pdf

 

[theoldwizard1]

Here is a better chart. For a 3% voltage drop at 10A and a total (round trip) distance of 63' (close to 2 x 10m) you need 6 gauge wire. For a 20A load it jumps to 2 gauge.

12v voltage drop charts