Hi every one
My brother in law is trying to charge a BIG battery of a Range rover with a 6amp charger to speed things up if we connect a second 6amp charger to the battery will this help / speed the charging ?
the battery is off the vehicle
Jacko

Rull of thumb is divide the amp hours by 12 -- as Range Rover batteries are generally 65 to 80 AH an 6 amp charger is about the right size

Typically you can charge lead-acid batteries much faster than that but as always with these batteries, make sure you have good ventilation and don't connect and (especially) disconnect the leads while the charger is active as the spark can ignite any hydrogen gas which might be present. Also keep an eye on the battery temperature - if it gets noticeably warm (towards "hot" ) then stop. Slightly warm is fine.

Here is an article which says that C/3 is a "typical" figure but says you can usually charge even faster than that:

http://www.powerstream.com/SLA-fast-charge.htm

If you do want to use two chargers then you should be able to connect them both up in parallel (all reds together, all blacks together) but if your chargers are electronic then they might sense each other and give some odd results. If in doubt then best to be patient.

Edit: At C/3, for a 60 AHr battery it would require 20 amps of charge current.


[Edited on 29/12/2012 by craig1410]

His not joking about the hydrogen given off. I blew a battry up when installing in the rear of a MGB. Had dropped it into place which released loads of gas off the plates, there was a tiny spark when i connected up and BANG, acid everywhere and the battery blown to pieces! Got away very lightly and ears ringing for an hour after.

Yeah I usually charge outside if possible as the breeze helps ventilation. Hydrogen is much lighter than air so will escape easily but it is also very highly flammable as you found out. Best bet is to power off the charger then wait a few minutes before disconnecting. Even better give it a good waft with a bit of cardboard or something to chase away any trapped gas.

Scariest thing I ever saw with batteries was when I stopped to help an old guy who had broken down at the side of the street. His battery was flat and he had jump leads but needed another car obviously. He seemed like a practical sort of guy (probably an old-school AA member...) so I popped the bonnet and let him connect it up. My engine was still running at the time. I think the sodium street lights must have confused him because he connected the jump leads the wrong way round and basically blew his leads to bits! A big shower of sparks and molten metal! I nearly shat myself!

Anyway, it didn't cause any damage to my car thankfully and I gave him a bump start instead!

Fast charging ruins batteries I have chargers that boost batteries at 30 amp but that is strictly only for extreme non-start emergencies. A fast high current rate charge on badly discharge battery cannot fully charge the battery and will reduce the batteries capcity

On dumb chargers the charging current rate is controlled purely by the charging voltage so connecting two 6 amp chargers in parallel won't charge at 12 amps but it may charge at 8 or 9 amps depending on the internal resistance of the chargers.

Sticking to old fashion lead-acid technology
A completely flat lead-acid battery will initially accept only a tiny current or zero current after a couple of hours on charge the current will ramp up, then as full charge is approached the current falls off, the third stage of charging is the float charge drring which the current is very low but it allows the charge to spread more evenly accross the plates.


Quote http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

"Lead acid charging uses a voltage-based algorithm that is similar to lithium-ion. The charge time of a sealed lead acid battery is 12–16 hours, up to 36–48 hours for large stationary batteries. With higher charge currents and multi-stage charge methods, the charge time can be reduced to 10 hours or less; however, the topping charge may not be complete. Lead acid is sluggish and cannot be charged as quickly as other battery systems."


The battery is fully charged when the current drops to a pre-determined level or levels out in stage 2. The float voltage must be reduced at full charge.
Courtesy of Cadex
During the constant-current charge, the battery charges to 70 percent in 5–8 hours; the remaining 30 percent is filled with the slower topping charge that lasts another 7–10 hours. The topping charge is essential for the well-being of the battery and can be compared to a little rest after a good meal. If deprived, the battery will eventually lose the ability to accept a full charge and the performance will decrease due to sulfation. The float charge in the third stage maintains the battery at full charge.

ha i do love you lot ...
i work in the plant world where money is everything .............
if we have a machine down on site we wont hesitate to connect it to the on van 24 volt charger and give it a goosing to start it in 2/3 mins but we are not worried about life of battery ...at all ... as long as the machine is running end of ... we can go and get new now it is started ..
all i can tell you from 36 yrs experience is
if a battery is us it wont come good
the harder you charge it and use it the shorter the life span
and those smart chargers keep batteries alive and revive batteries really well ..
to the extent we have bought one for work and we run 450 machines ..
HTH
les g

I had a battery on the Nissan which was not up to the job and I replaced it then put it in the shed where it stood for a few months till I was messing about one day and stuck the Optimate on it. The red light came on the charger to desulphate it so I left it to it's own devices and three days later the red light went out and it went to the charging cycle. It finished the charge and the battery went on my daughter's Corsa 1.2 where it stayed for 3 years and was still on and working when the car went.

The battery we are charging with a 6 amp charger is 110ah so how long will it take to charge it ? the battery was flat
jacko

I would just like to thank every one that has helped me we have got the Rover started and mot'ed this morning
Jacko