laptop chargers in series

[friedwires]

i have a pair of 19v 3.7a laptop chargers.i'd like to run them in series to use as a 36v charger.the problem is when i tie them together,the indicator on one starts to blink,and the pair only put out 19v.if i unplug the charger thats blinking, the voltage reading jumps up to 38v and slowly drops back down to 19v. i imagine thats just the caps discharging.i'm hoping one of you guys know how to make this work. i really need a low budget charging solution,and these were on hand........thanks

 

[Jeremy Harris]

Sounds like they may not be isolated, which is odd. When you say you have them connected in series, do you mean like this:

This should work, unless the laptop supplies have some sort of odd load sensing that makes them shutdown with nothing connected. My limited experience has been that laptop supplies are usually just dumb switch mode supplies, so if wired as above they should work OK.

Jeremy

 

[friedwires]

thanks for the reply Jeremy.thats the way i wired them.the same as batteries in series.i gave it another try today and got the same results.im stumped???

 

[texaspyro]

Sounds like they may not be isolated, which is odd.

Odd indeed, they could not get UL,CSE, etc approval if they were not.

 

[friedwires]

the chargers are from china.there are no UL markings on them.they are marked with CE if that means anything.im still kinda new with electronics.could you explain what you mean by isolated?

 

[thewmatusmoloki]

Do the charger's have an "earth" or 3rd pin on the plug at the bottom? If so they may not be isolated.

 

[friedwires]

after about 10 minutes of research here on ES,i learned what isolation means and found out all i needed to was snap the ground pins off of the ac plugs.so now i have 38v which is great! but will these chargers turn off when my pack reaches full charge?

 

[heathyoung]

Nope - they will continue to provide 38V.

 

[friedwires]

well that sucks.would it be possible to monitor the charge with an ammeter at first to determine the time it takes to charge the pack fully? if so it would just be a matter of setting a timer,and occasionally recalibrating to adjust for loss of capacity with age.i did'nt mention it before,but this will be used for sla's.

 

[thewmatusmoloki]

would it be possible to monitor the charge with an ammeter at first to determine the time it takes to charge the pack fully?

Yes.

would just be a matter of setting a timer,and occasionally recalibrating to adjust for loss of capacity with age

I'm certainly no expert and could be wrong, but in my experience a few of the chargers I've had seemed to drain the battery if left connected when turned off. It wasn't a heavy drain but still existed. So you would probably need to physically disconect the charger when the battery is full.

 

[Ypedal]

38v / 3 = 12.6v

the laptop chargers are not going to fully charge your pack even if you leave them on for days. you need a bit more to get them into the 13.x range and hold them there for a while.

 

[thewmatusmoloki]

Agreed, this also is truly true Yman.

 

[friedwires]

thanks again for the replies guys! you're right about the voltage.i'll need more like 40-42 volts to get a full charge.i think i'll have to go to plan B,and paralell charge with an automotive charger.what i have is a small atv with a brushed 36v 80a tennant sweeper motor on it.its powered by a kelly 20036,and 6 18ah sla's wired series paralell for 36v.the setup works great,and has a ton of power.the thing spins tires til it hits lvc.the runtime is'nt too bad either. about 40 minutes with the little guy on it.i'm also planning to gear it way down for more runtime.right now it will do 25mph.what sucks is he has to wait till the next day to ride it again.i was hoping to stay away from paralell charging because of all the wiring.i guess with my non existing budget,i'll have to go that rout. will it be possible to run 12 wires from the batteries to a plug for paralell charging while leaving the series wiring connected but turned off?View attachment 3