OT - Battery Charging
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Posts: 46,084
I have a robot that is powered by a pair of 12v SLA batteries in parallel.
What should I consider to be able to safely charge both batteries at the
same time on a single 12A charger? Is there a "distribution block" or
something similar available?
Thanks!
---
Jeff Abrams
jeff@m...
SUPERCHARGED & INTERCOOLED 2.5 liter 1993 Mazda MX-3 GS
http://www.mazdamaniac.com
TURBOCHARGED & INTERCOOLED 1.8 liter 1997 Mazda MX-5 Miata
If you're a cowboy and you're dragging a guy behind your horse, I bet
it would really make you mad if you looked back and the guy was reading a
magazine.
What should I consider to be able to safely charge both batteries at the
same time on a single 12A charger? Is there a "distribution block" or
something similar available?
Thanks!
---
Jeff Abrams
jeff@m...
SUPERCHARGED & INTERCOOLED 2.5 liter 1993 Mazda MX-3 GS
http://www.mazdamaniac.com
TURBOCHARGED & INTERCOOLED 1.8 liter 1997 Mazda MX-5 Miata
If you're a cowboy and you're dragging a guy behind your horse, I bet
it would really make you mad if you looked back and the guy was reading a
magazine.
Comments
>I have a robot that is powered by a pair of 12v SLA batteries in parallel.
>What should I consider to be able to safely charge both batteries at the
>same time on a single 12A charger? Is there a "distribution block" or
>something similar available?
Healthy lead-acid batteries will share the incoming current according to
how many amp-hours have been removed from each battery. Since you're
discharging these in parallel they should both draw approximately the same
current on recharge. The main concern I would have with charging SLA
batteries is the size of your charger. A 12-amp charger is big enough to
charge a 120 amp-hour battery, or two 60 amp-hour ones in parallel. If
they're much smaller you might want to watch out for overheating. This
assumes the usual manufacturer's caution to not exceed a charge rate in
amps that is 10% of the total ampere-hour rating. If they don't heat up
and don't vent, you should be OK. Final fully charged voltage while still
on charge probably shouldn't exceed about 2.45 volts per cell - 14.7 volts
overall - for best life.
73 de Jim, KB3PU
in amp-hours or less. If its a 10 aH battery you need a 1 amp charger.
Mouser sells some SLA chargers although the $20 battery tender type charger
I got from Harbor Freight works fine on my robot.
Original Message
> I have a robot that is powered by a pair of 12v SLA batteries in parallel.
> What should I consider to be able to safely charge both batteries at the
> same time on a single 12A charger? Is there a "distribution block" or
> something similar available?
I am using two 28Ah batteries in parallel. The charger is capable of 2A and
12A charge rates.
The problem I was running into previously was one battery or the other
burning out after a dozen or so charges.
The two batteries don't always discharge at the same rate since not all of
the circuitry is pulling from both batteries.
The temporary work around was to pull each of the fuses (both batteries are
fused independently) in turn to allow each battery to charge separately, but
this meant two charge cycles and the resultant time and attendance issues.
---
Jeff Abrams
jeff@m...
SUPERCHARGED & INTERCOOLED 2.5 liter 1993 Mazda MX-3 GS
http://www.mazdamaniac.com
TURBOCHARGED & INTERCOOLED 1.8 liter 1997 Mazda MX-5 Miata
I guess I kinda lost control, because in the middle of the play
I ran up and lit the evil puppet villain on fire. No, I didn't. Just
kidding. I just said that to help illustrate one of the human emotions,
which is freaking out. Another emotion is greed, as when you kill
someone for money, or something like that. Another emotion is generosity,
as when you pay someone double what he paid for his stupid puppet.
Original Message
From: Jim Higgins [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=nXOd3MnP1zSAvrFTrRg-Ks_E2IGwV3CQmv4n91rCch1uwkp5ygyPbfoisdDffswzMpjqCMDxDZa2]HigginsJ@s...[/url
Sent: Monday, October 07, 2002 5:16 PM
To: basicstamps@yahoogroups.com
Subject: Re: [noparse][[/noparse]basicstamps] OT - Battery Charging
At 16:37 10/07/02, Jeff Abrams wrote:
>I have a robot that is powered by a pair of 12v SLA batteries in parallel.
>What should I consider to be able to safely charge both batteries at the
>same time on a single 12A charger? Is there a "distribution block" or
>something similar available?
Healthy lead-acid batteries will share the incoming current according to
how many amp-hours have been removed from each battery. Since you're
discharging these in parallel they should both draw approximately the same
current on recharge. The main concern I would have with charging SLA
batteries is the size of your charger. A 12-amp charger is big enough to
charge a 120 amp-hour battery, or two 60 amp-hour ones in parallel. If
they're much smaller you might want to watch out for overheating. This
assumes the usual manufacturer's caution to not exceed a charge rate in
amps that is 10% of the total ampere-hour rating. If they don't heat up
and don't vent, you should be OK. Final fully charged voltage while still
on charge probably shouldn't exceed about 2.45 volts per cell - 14.7 volts
overall - for best life.
73 de Jim, KB3PU
>I am using two 28Ah batteries in parallel. The charger is capable of 2A and
>12A charge rates.
>The problem I was running into previously was one battery or the other
>burning out after a dozen or so charges.
>The two batteries don't always discharge at the same rate since not all of
>the circuitry is pulling from both batteries.
If not all of the circuitry is pulling current from both batteries at the
same then they aren't, strictly speaking, in parallel - at least not during
discharge. Regardless, if you parallel them before recharging you should
have no problem at the 2-amp setting. The 12-amp rate is too much for
batteries of that size even if they share the current 50/50. I think
that's your problem with short battery life.
SLA batteries are voltage/current sensitive. If the charger voltage is too
high, the current delivered at the end of charge will be too high and the
batteries will vent, causing them to dry out. They will probably overheat
also. Similar problems if you try to recharge too quickly. Overcharge
that causes the battery to dry out is a common failure mode for SLA batteries.
>The temporary work around was to pull each of the fuses (both batteries are
>fused independently) in turn to allow each battery to charge separately, but
>this meant two charge cycles and the resultant time and attendance issues.
Like I said, this shouldn't be an issue at the 2-amp rate. At the 12-amp
rate the battery that is deepest discharged will draw more of the current
and 12 amps is too much even if they were to share 6 amps each equally. If
you're recharging separately at the 2-amp setting, I don't see why you
couldn't just go ahead and recharge in parallel safely. It would take
longer, but no longer than recharging separately. I'm assuming we both
have the same definition of "parallel." My definition involves a direct
connection from negative terminal of one battery to negative terminal of
the other battery, and a direct connection from positive terminal to
positive terminal.
Jim H
the 12 amp charge rate. Its possible it may work fine on the 2 amp setting,
but most automotive chargers will still boil out batteries if the charger is
left on after the battery is charged.
Check out the SLA chargers:
http://www.mouser.com/index.cfm?handler=fra_pdfset&pdffile=621
This is what I use on my SLA and maintenance-free motorcycle batteries:
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=38895
Original Message
> >I am using two 28Ah batteries in parallel. The charger is capable of 2A
and
> >12A charge rates.
> >The problem I was running into previously was one battery or the other
> >burning out after a dozen or so charges.
> >The two batteries don't always discharge at the same rate since not all
of
> >the circuitry is pulling from both batteries.
>
> If not all of the circuitry is pulling current from both batteries at the
> same then they aren't, strictly speaking, in parallel - at least not
during
> discharge. Regardless, if you parallel them before recharging you should
> have no problem at the 2-amp setting. The 12-amp rate is too much for
> batteries of that size even if they share the current 50/50. I think
> that's your problem with short battery life.
>
> SLA batteries are voltage/current sensitive. If the charger voltage is
too
> high, the current delivered at the end of charge will be too high and the
> batteries will vent, causing them to dry out. They will probably overheat
> also. Similar problems if you try to recharge too quickly. Overcharge
> that causes the battery to dry out is a common failure mode for SLA
batteries.
>
> >The temporary work around was to pull each of the fuses (both batteries
are
> >fused independently) in turn to allow each battery to charge separately,
but
> >this meant two charge cycles and the resultant time and attendance
issues.
>
> Like I said, this shouldn't be an issue at the 2-amp rate. At the 12-amp
> rate the battery that is deepest discharged will draw more of the current
> and 12 amps is too much even if they were to share 6 amps each equally.
If
> you're recharging separately at the 2-amp setting, I don't see why you
> couldn't just go ahead and recharge in parallel safely. It would take
> longer, but no longer than recharging separately. I'm assuming we both
> have the same definition of "parallel." My definition involves a direct
> connection from negative terminal of one battery to negative terminal of
> the other battery, and a direct connection from positive terminal to
> positive terminal.
FLOW' IT DOESN'T DICTATE HOW MUCH CURRENT FLOWS IN EITHER OF THE PATHS.
I MEAN STRICTLY SPEAKING THAT IS, OR AM I MISSING SOMETHING HERE?
LEROY
If not all of the circuitry is pulling current from both batteries at
the
same then they aren't, strictly speaking, in parallel - at least not
during discharge. Regardless, if you parallel them before recharging
you should have no problem at the 2-amp setting. The 12-amp rate is too
much for batteries of that size even if they share the current 50/50. I
think
that's your problem with short battery life.
SLA batteries are voltage/current sensitive. If the charger voltage is
too high, the current delivered at the end of charge will be too high
and the batteries will vent, causing them to dry out. They will
probably overheat also. Similar problems if you try to recharge too
quickly. Overcharge that causes the battery to dry out is a common
failure mode for SLA batteries.
>The temporary work around was to pull each of the fuses (both batteries are
>fused independently) in turn to allow each battery to charge separately, but
>this meant two charge cycles and the resultant time and attendance issues.
Like I said, this shouldn't be an issue at the 2-amp rate. At the
12-amp
rate the battery that is deepest discharged will draw more of the
current
and 12 amps is too much even if they were to share 6 amps each equally.
If you're recharging separately at the 2-amp setting, I don't see why
you
couldn't just go ahead and recharge in parallel safely. It would take
longer, but no longer than recharging separately. I'm assuming we both
have the same definition of "parallel." My definition involves a direct
connection from negative terminal of one battery to negative terminal of
the other battery, and a direct connection from positive terminal to
positive terminal.
Jim H
Original Message
From: "Jim Higgins" <HigginsJ@s...>
Final fully charged voltage while still
> on charge probably shouldn't exceed about 2.45 volts per cell - 14.7 volts
> overall - for best life.
**********************
Jim:
I have an automatic SLA charger that doesn't drop back to trickle until
14.85V. I haven't killed any batteries yet, but do you think this voltage
is too high?
Thanks,
Ray McArthur
after a deep discharge cicle.
A battery with deep discharge to 6 volt (1 volt per cell) may never recover if
left uncharged by a couple days.
ACJacques
Jeff Abrams gravada:
> Thanks.
>
> I am using two 28Ah batteries in parallel. The charger is capable of 2A and
> 12A charge rates.
> The problem I was running into previously was one battery or the other
> burning out after a dozen or so charges.
> The two batteries don't always discharge at the same rate since not all of
> the circuitry is pulling from both batteries.
>
> The temporary work around was to pull each of the fuses (both batteries are
> fused independently) in turn to allow each battery to charge separately, but
> this meant two charge cycles and the resultant time and attendance issues.
>
> ---
>
> Jeff Abrams
> jeff@m...
>
> SUPERCHARGED & INTERCOOLED 2.5 liter 1993 Mazda MX-3 GS
> http://www.mazdamaniac.com
> TURBOCHARGED & INTERCOOLED 1.8 liter 1997 Mazda MX-5 Miata
>
> I guess I kinda lost control, because in the middle of the play
> I ran up and lit the evil puppet villain on fire. No, I didn't. Just
> kidding. I just said that to help illustrate one of the human emotions,
> which is freaking out. Another emotion is greed, as when you kill
> someone for money, or something like that. Another emotion is generosity,
> as when you pay someone double what he paid for his stupid puppet.
>
>
Original Message
> From: Jim Higgins [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=sUMaLnewvQUCktph3wYZjxvjDhwKfgHmuu5UCTx_9wArGBBI4xHN-g_44dJoxlX7fUIVYD2PJQawaY8]HigginsJ@s...[/url
> Sent: Monday, October 07, 2002 5:16 PM
> To: basicstamps@yahoogroups.com
> Subject: Re: [noparse][[/noparse]basicstamps] OT - Battery Charging
>
> At 16:37 10/07/02, Jeff Abrams wrote:
>
> >I have a robot that is powered by a pair of 12v SLA batteries in parallel.
> >What should I consider to be able to safely charge both batteries at the
> >same time on a single 12A charger? Is there a "distribution block" or
> >something similar available?
>
> Healthy lead-acid batteries will share the incoming current according to
> how many amp-hours have been removed from each battery. Since you're
> discharging these in parallel they should both draw approximately the same
> current on recharge. The main concern I would have with charging SLA
> batteries is the size of your charger. A 12-amp charger is big enough to
> charge a 120 amp-hour battery, or two 60 amp-hour ones in parallel. If
> they're much smaller you might want to watch out for overheating. This
> assumes the usual manufacturer's caution to not exceed a charge rate in
> amps that is 10% of the total ampere-hour rating. If they don't heat up
> and don't vent, you should be OK. Final fully charged voltage while still
> on charge probably shouldn't exceed about 2.45 volts per cell - 14.7 volts
> overall - for best life.
>
> 73 de Jim, KB3PU
>
> To UNSUBSCRIBE, just send mail to:
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>STRICTLY SPEAKING THE WORD 'PARALLEL' MEANS 'MULTIPLE PATHS FOR CURRENT
>FLOW' IT DOESN'T DICTATE HOW MUCH CURRENT FLOWS IN EITHER OF THE PATHS.
>I MEAN STRICTLY SPEAKING THAT IS, OR AM I MISSING SOMETHING HERE?
That would be a reasonable general definition for general electronic
circuits, but when you're talking about two *batteries* in parallel and
each has only two terminals, one positive and one negative... well, there
just aren't too many possibilities as far as current paths from the batteries.
As far as the magnitude of current flow to/from the batteries on charge or
discharge I deliberately failed to address the flow on discharge and I said
(in an earlier posting) that the charge current would be shared, with the
battery which was discharged the most getting the most current.
So, yes, you may have missed something that may have been contained in my
earlier posting(s) which this one built upon. If the above doesn't clear
it up, I'll be glad to help, but you'll need to make your question more
specific.
Jim H
Jim Higgins wrote:
>>If not all of the circuitry is pulling current from both batteries at the
>>same [noparse][[/noparse]time] then they aren't, strictly speaking, in parallel - at least
>>not during discharge. Regardless, if you parallel them before recharging
>>you should have no problem at the 2-amp setting. The 12-amp rate is too
>>much for batteries of that size even if they share the current 50/50. I
>>think that's your problem with short battery life.
>>
>>SLA batteries are voltage/current sensitive. If the charger voltage is
>>too high, the current delivered at the end of charge will be too high and
>>the batteries will vent, causing them to dry out. They will probably
>>overheat also. Similar problems if you try to recharge too
>>quickly. Overcharge that causes the battery to dry out is a common
>>failure mode for SLA batteries.
>>
>> >The temporary work around was to pull each of the fuses (both batteries are
>> >fused independently) in turn to allow each battery to charge
>> separately, but
>> >this meant two charge cycles and the resultant time and attendance issues.
>>
>>Like I said, this shouldn't be an issue at the 2-amp rate. At the 2-amp
>>rate the battery that is deepest discharged will draw more of the current
>>and 12 amps is too much even if they were to share 6 amps each
>>equally. If you're recharging separately at the 2-amp setting, I don't
>>see why you couldn't just go ahead and recharge in parallel safely. It
>>would take longer, but no longer than recharging separately. I'm
>>assuming we both have the same definition of "parallel." My definition
>>involves a direct connection from negative terminal of one battery to
>>negative terminal of the other battery, and a direct connection from
>>positive terminal to positive terminal.
>>
>>Jim H
>
Original Message
>From: "Jim Higgins" <HigginsJ@s...>
> > Final fully charged voltage while still on charge
> > probably shouldn't exceed about 2.45 volts
> > per cell - 14.7 volts overall - for best life.
>*********************
>
>Jim:
>I have an automatic SLA charger that doesn't drop back to trickle until
>14.85V. I haven't killed any batteries yet, but do you think this voltage
>is too high?
No, not too high if it is a two or three-step charger that drops back when
that voltage is reached. It is a sustained constant voltage above 14.7
without dropping back that is the killer.
Do you know what voltage yours drops back to once it reaches 14.85
volts? More importantly, it should drop back to a very low current, at
which point voltage matters less. It's current that heats the battery and
causes the cells to vent and dry out.
73 de Jim, KB3PU
>Remember also SLA batteries will have short life if not charged
>immediatelly after a deep discharge cicle.
>A battery with deep discharge to 6 volt (1 volt per cell) may never
>recover if left uncharged by a couple days.
Yes! And some will never recover even if recharged immediately. It
depends on whether the discharge to 1 volt per cell is performed at a
relatively high current or low current. At a relatively high current is
far less damaging than at a low current. A SLA battery that is deeply
discharged using a low current is prone to use up all the acid in the cell
and then the lead compounds in the plates will dissolve (slightly) in the
weak electrolyte and will tend to form shorts thru the separators when the
battery is recharged. Discharge to 1 volt per cell is not a real good idea
at any rate.
73 de Jim, KB3PU
> that voltage is reached. It is a sustained constant voltage above 14.7
> without dropping back that is the killer.
>
> Do you know what voltage yours drops back to once it reaches 14.85
> volts? More importantly, it should drop back to a very low current, at
> which point voltage matters less. It's current that heats the battery and
> causes the cells to vent and dry out.
*******************
About 13.85 volts.
Thanks,
Ray McArthur
>I have an automatic SLA charger that doesn't drop back to trickle until
>14.85V. I haven't killed any batteries yet, but do you think this voltage
>is too high?
Sounds about right to me. My SLA chargers stay in charge mode until 14.90
.. 15.00V, then drop to 13.5V in float mode.
dwayne
--
Dwayne Reid <dwayner@p...>
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
(780) 489-3199 voice (780) 487-6397 fax
Celebrating 18 years of Engineering Innovation (1984 - 2002)
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> > No, not too high if it is a two or three-step charger that drops back when
> > that voltage is reached. It is a sustained constant voltage above 14.7
> > without dropping back that is the killer.
> >
> > Do you know what voltage yours drops back to once it reaches 14.85
> > volts? More importantly, it should drop back to a very low current, at
> > which point voltage matters less. It's current that heats the battery and
> > causes the cells to vent and dry out.
>*******************
>
>About 13.85 volts.
You seem to have a very nice charger there. Maybe others would benefit
from knowing the make and model number.
Jim H
>
> You seem to have a very nice charger there. Maybe others would benefit
> from knowing the make and model number.
>
> Jim H
**************
Thanks Jim
It is a Powersonic model 12800 made for SLAs. 12 volts, 800 ma max. If I
remember correctly, it sells for ~$40.
Ray McArthur
You need to charge the batteries independently. Ideally a two stage
charger, the first stage is a "bulk" current limited phase, until a
particular voltage/per cell is reached. Then a float charge phase is
entered, which is voltage limited. I'm sure Maxim does a chip for this.
The specific battery info, charge currents etc, will be available from
the battery manufacturer.
Typical charge details 0.4 Amp/AmpHr capacity, to a maximum of about
2.35v/cell (14.1 V for 6 cell "12" Volt SLA battery) then "float", but
check with the battery manufacturer. Try the link below for charger IC
details.
http://dbserv.maxim-ic.com/quick_view2.cfm?qv_pk=2308
Rob
Original Message
From: Jeff Abrams [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=ErcAKah1eV4NaGunYjIzP24_z_1ay6_OcGZ-cDlhwCnJeZqYaCuJetSTkiUl46E_VjMLe33-TkWcn8jMR5zmOg]clavier@b...[/url
Sent: 07 October 2002 23:25
To: basicstamps@yahoogroups.com
Subject: RE: [noparse][[/noparse]basicstamps] OT - Battery Charging
Thanks.
I am using two 28Ah batteries in parallel. The charger is capable of 2A
and
12A charge rates.
The problem I was running into previously was one battery or the other
burning out after a dozen or so charges.
The two batteries don't always discharge at the same rate since not all
of
the circuitry is pulling from both batteries.
The temporary work around was to pull each of the fuses (both batteries
are
fused independently) in turn to allow each battery to charge separately,
but
this meant two charge cycles and the resultant time and attendance
issues.
---
Jeff Abrams
jeff@m...