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Discussion Starter · ·
How can I =91dump=92 charge a small pack from a big pack,
is there a simple way to do that? =

If I have 16 8v 190ah flooded lead acid batteries
which when fully charged are about 133v then could I
divide that amongst 9 12v 28ah high output AGM
batteries to charge at 14.7 volts each?

harry

Albuquerque, NM
http://geocities.com/hendersonmotorcycles/blog.html
http://www.austinev.org/evalbum/1221
http://geocities.com/solarcookingman

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Discussion Starter · ·
The simple way is with one of Rich's PFC50's or a PWM controller, but these=
both cost money. =

Dump charging on the cheap requires a bit of trial and error. Basically yo=
u are using the higher voltage of the larger pack to force current through =
the smaller pack, and the larger the difference in the packs the more curre=
nt you will get. I played with it on my motorcycle a bit, but decided it d=
id not fit my needs. It's easy to dump charge through the bulk charge phas=
e, but dangerous during the finish charge. It is fun to charge at 100's of=
amps though

Here is what happens. When you first start you will have the highest curre=
nt as you will have the largest voltage differential. The current is deter=
mined by this voltage difference and the totally resistance in your charge =
circuit. I just used 2 large cables and a beafy contactor. The voltage on=
the pack you are charging starts coming up and the voltage on the pack you=
are charging from starts to sag so the current drops off. To overcome thi=
s you can break the circuit and add another battery on the charging side, b=
ut this is when things start getting tricky since you now have unequal batt=
eries that you are charging from. The next tricky part comes when the volt=
age on the battery you are charging starts to fill up. If you are still pu=
shing big current, things can go bad in a hurry.

The two packs you describe below seem like they might work well together. =
It's easy to test, you just need some beefy cables and a nice big switch/co=
ntactor. I would guess that it will work fairly well through the bulk phas=
e, but not be quite enough to bring everything up to 14.7 volts. You might=
need one more 8 volter for that.

damon

> Date: Thu, 20 Sep 2007 12:32:31 -0700
> From: [email protected]
> To: [email protected]; [email protected]
> Subject: [EVDL] Dragster question2
>
>
> How can I =91dump=92 charge a small pack from a big pack,
> is there a simple way to do that?
>
> If I have 16 8v 190ah flooded lead acid batteries
> which when fully charged are about 133v then could I
> divide that amongst 9 12v 28ah high output AGM
> batteries to charge at 14.7 volts each?
>
>
> harry
>
> Albuquerque, NM
> http://geocities.com/hendersonmotorcycles/blog.html
> http://www.austinev.org/evalbum/1221
> http://geocities.com/solarcookingman
>
>
> _________________________________________________________________________=
___________
> Fussy? Opinionated? Impossible to please? Perfect. Join Yahoo!'s user pan=
el and lay it on us. http://surveylink.yahoo.com/gmrs/yahoo_panel_invite.as=
p?a=3D7
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev

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Discussion Starter · ·
Generally the point of a "dump" pack is to do a quick high current charge
of a lower voltage pack.
The key here is "High current"

Keep in mind what happens to lead-acid batteries when delivering high
current, their voltage sags.

The voltage under load of your flooded pack will probably drop to 117
volts or less.
This will only deliver about 13 volts to each of your AGMs. That might be
enough to start charging them if they have a low SOC, but as they get
fuller you'll probably need to add another battery to the flooded pack.

However; if you aren't going for a quick charge, and only want to bring
the AGMs up to perhaps 80% SOC, then it should work ok.

>
> How can I =91dump=92 charge a small pack from a big pack,
> is there a simple way to do that?
>
> If I have 16 8v 190ah flooded lead acid batteries
> which when fully charged are about 133v then could I
> divide that amongst 9 12v 28ah high output AGM
> batteries to charge at 14.7 volts each?
>
>
> harry
>
> Albuquerque, NM
> http://geocities.com/hendersonmotorcycles/blog.html
> http://www.austinev.org/evalbum/1221
> http://geocities.com/solarcookingman
>
>
> ___________________________________________________________________=
_________________
> Fussy? Opinionated? Impossible to please? Perfect. Join Yahoo!'s user
> panel and lay it on us.
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>

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