Charging Battery in Situ?

[marcus1970]

Hello all,

Have a 12v 4 amp battery charger and a nice long lead.

I need to charge the battery whilst it's still in the car.

What's the best way to do it?

Cheers

MB

[Conian]

unplug neg lead from battery to car
attach charger

you may need to remove the caps from the top of the battery.

[Gazzab]

Put the pos connection on the battery and the neg on one of the air box metal upright fixings.

[JensenA]

Conian said:

unplug neg lead from battery to car
attach charger

you may need to remove the caps from the top of the battery.

ignore this and do as Gazzab advises. You don't have to remove any leads or bodywork, the positive lead will connect through the hole on the panel.

[Conian]

I was always told to disconnect the battery from the car by at least the neg lead while charging.

This may be one of those issues that many people in both camps (will the plane on the conveyor take off?)

Can I ask where/why/how you believe it's ok to leave it connected?
I'm not saying youre wrong, I wish to hear reasoning is all so that I can re-evaluate my thoughts on the process.

[Gazzab]

A charger shouldnt (IMHO) put too much strain on the system. Jump starting though can fry boxes etc

[RichB]

Conian said:

Can I ask where/why/how you believe it's OK to leave it connected?

Been charging batteries in-situ without disconnecting the leads for 40 years and never had a problem so I'm firmly in the don't do more than you need to camp. Perhaps it's a health & safety thing? Disconnecting the earth before doing anything is standard practice in most garages.

[kevin63]

One other point is that if you disconect the battery the alarm will keep sounding due to it's battery backup.

[kojak]

You are OK to charge in situ, if the charger ampage is no more than 7amp. Anymore can damage the electrical componants.

[Steve_T]

Conian said:

I was always told to disconnect the battery from the car by at least the neg lead while charging.

...

Can I ask where/why/how you believe it's ok to leave it connected?

The alternator charges the car this way.

[Tanguero]

kojak said:

You are OK to charge in situ, if the charger ampage is no more than 7amp. Anymore can damage the electrical componants.

The current is determined solely by the voltage of the supply and the resistance of the circuit. The current capacity of the charger has nothing to do with it.

[kojak]

Tanguero said:

kojak said:

You are OK to charge in situ, if the charger ampage is no more than 7amp. Anymore can damage the electrical componants.

The current is determined solely by the voltage of the supply and the resistance of the circuit. The current capacity of the charger has nothing to do with it.

Maybe. Maybe not. I'm no auto electrician. Thats what it says in the TVR manual though. Must be there for a reason.

[esso]

kojak said:

Tanguero said:

kojak said:

You are OK to charge in situ, if the charger ampage is no more than 7amp. Anymore can damage the electrical componants.

The current is determined solely by the voltage of the supply and the resistance of the circuit. The current capacity of the charger has nothing to do with it.

Maybe. Maybe not. I'm no auto electrician. Thats what it says in the TVR manual though. Must be there for a reason.

I have read this too!

[julian64]

Snow's in all your brains.

You can apply the charger straight to the car while the batteries in situ.

Current will not damage any component in your car. Voltage will.

The only thing you have to watch out for is how high the voltage on the charger goes to charge your battery.

1) You will never get a problem charging an 'okay' battery
2) you will never get a problem with a decent car charger.

You will however get a problem with a completely flat battery, and I mean flat as a pancake with a charger that doesn't have the ability to sense a dead battery. In this instance the charger increases the voltage to a level sufficent to charge the battery. Its this raise in voltage that will potentially harm you cars electrics. I would monitor the voltage and anything up to 14v will be fine. If the charger gets the voltage up to 18-19v to charge your dead battery something is going to get damaged, and quick .

[kojak]

julian64 said:

Snow's in all your brains.

.

It must have been snowing when the workshop manual was wrote.

Section I page 12.

"CAUTION: If charging the battery whilst still connected to the car a trickle charge giving no more than 7 amps must be used as a larger amp charger will cause damage to other components"

It put the sts up me when mine was flat.

[Tanguero]

Just because it is in the manual doesn't make it fact. I trump your manual with my Ph.D in physics...

[julian64]

kojak said:

julian64 said:

Snow's in all your brains.

.

It must have been snowing when the workshop manual was wrote.

Section I page 12.

"CAUTION: If charging the battery whilst still connected to the car a trickle charge giving no more than 7 amps must be used as a larger amp charger will cause damage to other components"

It put the sts up me when mine was flat.

Well V=IR and in the short term R is a constant. In a dud battery R is going to be very high.

In short

dud battery gets charged disconnected from the car.
good battery gets charged in situ.

[headcase]

Maybe the manual is just beig cautious as maybe it is possible to cause a short with the charger crocodile clips on the batt with it still in situ? Also depends on the quality of the charger, most chepo chargers use on half wave rectification with no regulation, these types of chargers will inject a real dirty voltage into your otherwise clean electrical system, this is no problem for the batt as it just soaks it all up but leaving the batt connected subjects the rest of the electronics to this dirty signal. I suppose cars using older technology like points and no black boxes then this makes no difference at all but personally i would be cautious with a car like the cerb.
If you have a charger that has a properly rectified, smoothed and regulated output (just like what you get from the alternator) then in car charging should be no problem at all.

[Jackal83]

If i had to do this alot or keep the battery on an optimate... Id make a small loom and attach it to the battery and bring it from under the top scuttle panal so its easy... on the end of the loom have a female 50amp plug alter your charger to have the plug on it also but male... then if you need to charge it lift the bonnet plug in to battery and trop your bonnet back down!!!

I think optmates come with this simple loom cos i have on on the ski!! very simple to do.

I've always charged in situ and never take battery off unless i wanna drop test is.....

[kojak]

Jackal83 said:

If i had to do this alot or keep the battery on an optimate..

Mines always connected to one while in the garage.