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Old 22nd January 2004, 05:10 PM   #11
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Quote:
Originally posted by Circlotron
If the car battery has a capacity of 40 ampere hours (fairly common size for ~3 litre engine) then 2 amps will charge it in about 20 hours.

Actually, it's not a good idea to deep discharge car batteries because the lead paste in the squares of the pure lead grid swells up and when it contracts upon recharge it pulls away from the grid and ceases to make electrical contact so the battery capacity gradually decreases till it fails. OTOH, car batteries are dirt cheap compared to deep cycle ones so just do whatever you like and big deal!
so a 1A charger will charge 1 amp in 1 hour? 20 hours is a long time but any current will charge them in theory? or do i need a certain amount as a minimum?

i wouldnt deep dischrage any battery. car batteries are cheap, and that is why i am using them, instead of SLA ones, which everyone keeps recomending. i cant afford ~150+ for 2 of the same capacity as car batteries.
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Old 24th January 2004, 04:47 PM   #12
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Hi!

1) you can use 2 IDENTICAL car batteries BUT remember they won't last long if you discharge them deeply; if you do this, at least charge them as soon as possible (they don't like to be kept discharged!)

2) Don't build a charger; building one is surely not so easy as someone told you! Battery chemistry is a complex thing, be wise!
I give you a small example: you set the voltage regulator at 28.4V but you can't control the intensity of current (Ampere) your battery can draw (depends by battery and state of charge) while charging; you can easily burn out everything.
buy a car battery charger (even a slow one is OK and it's very useful) and charge as the manual recommends;

3) For safety reason the only way to proceed is to use ALWAYS the 2 batteries as 1 only battery; I mean they should be charged/discharged at exactly the same time/amount; this is because you want to have the 2 batteries always with the same characteristics. I suggest charging them in parallel simply beacuse commercial chargers are usually rated at 12V (the charger will "see" twice the capacity in Ah of the single battery).

4) Be extremely careful using these batteries: do you know that a single car battery can easily give out ~ 400 A of current if it is short-circuited?? you know how much amout it is? So always double check and secure all wires and connections and, if possible, unplug the batteries and cover the connectors if nobody could look at them.

I'm quite expert about batteries. Don't hesitate to ask me more if you need to...

Only another thing..... How would you run this amp in a car without a dedicated PSU? In a car you have only one battery!!

Bye
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Old 25th January 2004, 07:28 PM   #13
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Quote:
Originally posted by Davide82
Hi!

1) you can use 2 IDENTICAL car batteries BUT remember they won't last long if you discharge them deeply; if you do this, at least charge them as soon as possible (they don't like to be kept discharged!)

2) Don't build a charger; building one is surely not so easy as someone told you! Battery chemistry is a complex thing, be wise!
I give you a small example: you set the voltage regulator at 28.4V but you can't control the intensity of current (Ampere) your battery can draw (depends by battery and state of charge) while charging; you can easily burn out everything.
buy a car battery charger (even a slow one is OK and it's very useful) and charge as the manual recommends;

3) For safety reason the only way to proceed is to use ALWAYS the 2 batteries as 1 only battery; I mean they should be charged/discharged at exactly the same time/amount; this is because you want to have the 2 batteries always with the same characteristics. I suggest charging them in parallel simply beacuse commercial chargers are usually rated at 12V (the charger will "see" twice the capacity in Ah of the single battery).

4) Be extremely careful using these batteries: do you know that a single car battery can easily give out ~ 400 A of current if it is short-circuited?? you know how much amout it is? So always double check and secure all wires and connections and, if possible, unplug the batteries and cover the connectors if nobody could look at them.

I'm quite expert about batteries. Don't hesitate to ask me more if you need to...

Only another thing..... How would you run this amp in a car without a dedicated PSU? In a car you have only one battery!!

Bye
1) i have been told this by everyone. i dont want to risk damaging them, so i am not going to dischrage them anywhere near fully.

2) i have looked at the price of car battery chargers, and i have desided it would be easier and safer to buy one.

3) i will be ok to charge them in parrallel?

4) yes, i know the short-term output of a car battery. i have seen a spanner melted by touching both terminals of a battery.

5) i am going to put the two batteries in my car (when i get one). i will have to take them out to charge them though.

PS: thanks for the offer of more advise. i will ask you if i have any questions.
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