Quick question please

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deacon
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Joined: 03/19/2009
Points: 55

Did anyone ever try charging a 30v diy battery pack with a 36v scooter charger. I'm considering building 30v battery packs and curious about charging.

Why 30v because it allows for some pedal assist 36v doesn't and does require so much as 24v. So if you know if gassing will be at critical mass let me know.

Also if you know the max charging rate of one of those chargers I might can find an answer somewhere. I just don't know. Thanks.

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sangesf
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Joined: 11/10/2008
Points: 142
Re: Quick question please

As a general rule, you can't do what you're thinking.
What type of batteries?
More info is needed to help you.

deacon
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Joined: 03/19/2009
Points: 55
Re: Quick question please

they are just regular old sla batteries two 12v and one 6v per string. Two to four strings on the charger at a time. I could break them down to use my 12/6 volt chargers on but the 36 would be so much easier.

e-doggies
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Joined: 12/30/2007
Points: 280
Re: Quick question please

If the electrolyte "boils" at about 14.7V for a 12V Battery, and at about 7.4V for a 6V Battery, you should not charge higher than 36.8V (14.7+14.7+7.4). 36V (nominal) chargers put out in excess of 39V.

sangesf
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Points: 142
Re: Quick question please

deacon wrote:

they are just regular old sla batteries two 12v and one 6v per string. Two to four strings on the charger at a time. I could break them down to use my 12/6 volt chargers on but the 36 would be so much easier.

The 12v 6v charger is the ONLY way you can do it..
That's what I'm doing right now.
You WILL boil the batteries with a 36v charger

deacon
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Points: 55
Re: Quick question please

Okay then how about a resister circuit added at the end of the battery charger to choke down the voltage. The charger at say 40v 1.5 amps would be putting out say 60 watts. I would probably want it to put out 36v at 1.5 or so amps. or say around 50 watts. So would a ten ohm resister do it for me or is my math all wrong.

deacon
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Points: 55
Re: Quick question please

Okay then how about a resister circuit added at the end of the battery charger to choke down the voltage. The charger at say 40v 1.5 amps would be putting out say 60 watts. I would probably want it to put out 36v at 1.5 or so amps. or say around 50 watts. So would a ten ohm resister do it for me or is my math all wrong.

colin9876
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Joined: 10/23/2008
Points: 289
Re: Capacitor not Resistor

Nice idea but a resistor wouldnt work because the 36v charger stops charging when it reads the voltage of the pack is 39v or whatever. Having a resistor on a 33v bank wont add that.
You would actually need a capacitor to add the extra 6 or so volts to the reading!

You can actually use the 36v charger as you first suggested AS LONG AS you disconnect it when ur pack gets to about 33volts.

The charger would only 'boil' the pack when the voltage climbs to high.
When the pack is at a lower voltage it pulls the output from the charger down to its own voltage. Its only the point at which it stops thats really the problem. You would need a voltmeter accross the pack and to disconnect the charger manually at the right time.
So no good if you just want to walk away and come back the next day fully charged!

sangesf
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Re: Capacitor not Resistor

colin9876 wrote:

Nice idea but a resistor wouldnt work because the 36v charger stops charging when it reads the voltage of the pack is 39v or whatever. Having a resistor on a 33v bank wont add that.
You would actually need a capacitor to add the extra 6 or so volts to the reading!

You can actually use the 36v charger as you first suggested AS LONG AS you disconnect it when ur pack gets to about 33volts.

The charger would only 'boil' the pack when the voltage climbs to high.
When the pack is at a lower voltage it pulls the output from the charger down to its own voltage. Its only the point at which it stops thats really the problem. You would need a voltmeter accross the pack and to disconnect the charger manually at the right time.
So no good if you just want to walk away and come back the next day fully charged!

I wouldn't suggest that either...
From my own experience, I've tried to use a 36v charger on 30v just like deacon is supposing, and within 5min on the charger (batts were at about 50% dod) I could hear the boiling...

It's just not worth taking the chance.
Just do what I do, I have a 24v 6a charger and my 12v/6v 6a charger and use them at the same time on my 2-12v 35ah and 1-6v 36ah SLAs.
On an average day, I'll use about 22 AH and charge them overnight.

deacon
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Joined: 03/19/2009
Points: 55
Re: Capacitor not Resistor

Sounds like the easiest thing for me would be to use the 36volt battery pack as is. Shame because I really like the 30v better.

One more question. I found some 30v power supplies 400ma which makes them slightly under half amp They would probably work for a trickle charger. Any thoughts on this. My plan was to build two packs one resting while one is running. I have the batteries on hand to build three 36v or pick up some 6v and build four 30v. So the trickle charger would probably work. I ran a pack down pretty far, about as far as I run them down anyway, yesterday and my 36v 1.5 ah took about four or five hours to charge. So in theory the 400ma could have it ready over night.

So how about it any suggestions.

Ps im not sure my cheap scooter charger actually shuts down at all.

sangesf
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Joined: 11/10/2008
Points: 142
Re: Capacitor not Resistor

There is a $50 4.0 amp charger on tncscooters dot com that works awesome for 36v sla (I've actually ordered one a long time ago) and it measured 4.2 amps..
It Is pink but who cares.

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