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Battery Charger

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Battery Charger

On all my previous car I have just connected the battery charger to the battery without disconnecting the car battery leads and had no problems but looking at the workshop manual of my current car (Honda) it clearly states the battery should be disconnected before charging.
Anyone got any opinions or advice about this ?
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Re: Battery Charger

I'm like you, ive just connected the charger leaving everything connected
however  Roll eyes
at the end of charge a lead acid battery should go up to 2.7 volts per cell that is 16.2 volts on a 12 volt battery. maybe Honda know this could harm something.
Also an extra load connected in parallel with the battery may reduce the current the battery sees thus reducing the charge or increasing the time needed.  Wink
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itsme
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Re: Battery Charger

and what would the voltage be from the alternator?
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Re: Battery Charger

Dont know, but LA batteries start gassing at 2.3 volts per cell or thereabouts. modern  "maintenance free" batteries will be charged at something less than this, by the alternator to prevent electrolyte loss.
my advice would be like Honda's if you were going properly charge a battery, equivalent  to a "bench charge" then check the characteristics of the charger and connect it to the battery with whatever preparation is recommended. This used to be the removal of the filler plugs but not any more.  Smiley
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Re: Battery Charger

The reason you should disconnect the battery earth lead, (minimum requirement), is to prevent spurious voltages and current, from circulating on the car electrics.
  As you have now checked in the manual, and it says this is the way to do it, be thankful that previous efforts have done no damage, and proceed in accordance with the manual from now on.!  Wink
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Re: Battery Charger

I have ALWAYS disconnected the battery, as feeding charge backwards through any circuit is not usually a good idea - particularly with the amount of electronics used in modern cars.
The advice from -
http://www.halfords.com/webapp/wcs/stores/servlet/ACArticleDisplay?storeId=10001&langId=-1&articleId...
http://www.carbasics.co.uk/how_to_charge_car_battery.htm
http://www.rac.co.uk/forum/showthread.php?2233-Charging-car-battery
also suggest disconnecting at least the earth lead first.
What does your Honda handbook say about emergency starting the engine from another battery using jump leads ?, as that is not dissimilar from the charging scenario other than the voltage will be lower but the current required will be significantly greater !
itsme
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Re: Battery Charger

Feeding charge backwards  Grin Grin
What is connected to the battery when the ignition is off and are these at risk if over voltage?
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Re: Battery Charger

Another factor is that sometimes on some models, disconnecting the battery will delete the security code for the radio and you will not beable to use it. Anti theft device. NB It would have not been a built-in one,  as in modern dashboards which are immune.
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Re: Battery Charger

I've always disconnected it and removed from the car to charge inside. I usually put the spare in the car to keep it usable and the locking working etc. I've had a few mishaps with the battery and power surges in the car in the past.. once managing to kill the central locking system completely. It did recover.. months later but I still get many quirky moments with the locking now. Also nearly blew one battery once.. jump started a lady, got talking to her and crossed the two clips I'd just taken off her battery while still connected to mine - sparks everywhere  Shocked
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Re: Battery Charger

Quote from: itsme
and what would the voltage be from the alternator?
I Think the voltage from the alternator is around 19.5 volts but the current gets rectified to around 13 volts. One of the first signs that the rectifier is failing is that your car light bulbs fail at frequent intervals (ie burn out)
Quote from: colintivy
Another factor is that sometimes on some models, disconnecting the battery will delete the security code for the radio and you will not beable to use it. Anti theft device. NB It would have not been a built-in one,  as in modern dashboards which are immune.
I Had thought to solve the problem by using a memory storage device which is powered by a 9 volt battery and plugs into the cigarette lighter but unfortunately no live connection exists at this connector until the ignition key is moved into the auxillary position as I found out when I tried to use a 12volt tyre inflator.
Guess I will just go ahead and disconnect the battery as most of the responses appear to favour this meathod.
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Re: Battery Charger

Quote from: purleigh

What does your Honda handbook say about emergency starting the engine from another battery using jump leads ?, as that is not dissimilar from the charging scenario other than the voltage will be lower but the current required will be significantly greater !

I disagree.... when you put jump leads onto the car battery, it is the same as removing the battery and using another one to start the engine.... (however, that is impracticable, as when you remove the battery the engine stops !.)... One point that should be noted, instead of putting the Earth connection onto the battery terminal, it should be made direct to the ENGINE FRAME... being careful to observe the correct polarity, of course !
itsme
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Re: Battery Charger

Quote from: shutter

I disagree.... when you put jump leads onto the car battery, it is the same as removing the battery and using another one to start the engine....

That is completely incorrect. When you jump a car it's can be compared with connecting to the flat battery to a charger. If you just leave the two cars connected without trying to start the car the flat battery will charge and after some time you will be able to disconnect the jump leads and start the car using it's own battery.
The problem arise when trying to jump a car if the charging current demand of the battery and the current needed to start the car is greater than what the running car can supply, the car will not start. Then a small period of time is needed to allow the charging current to drop before trying to start the car.
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Re: Battery Charger

Correct. We had a small Polo, our neighbour a large Rover 3500 and he flattened his battery. The first time we tried to jump start it I hadn't raised the revs on the Polo and as soon as he engaged the starter motor the Polo stalled. With the Polo revs held at about 1500 we got his car started.
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Re: Battery Charger

Reminds me of a range rover I jumped last year. Great big 6L thing it was and some dappy woman had left her headlights on. I offered to jump her with my volvo lump and the look of shock and horror on her face said it all "That'll never do it".
I hooked up the leads and told her to start hers. She even said to me I'd need to put my foot down a bit - I didn't bother as I knew my beast well.. she turned her key and the RR started in two turns of the engine  Cool
Can't knock a volvo lump Wink
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VileReynard
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Re: Battery Charger

The reason you are supposed to remove the battery is that any gases (Hydrogen, Oxygen) produced are explosive.  Cheesy