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[DPRG] Remedial Circuitry

Subject: [DPRG] Remedial Circuitry
From: Karim Virani karim at compuguru.com
Date: Wed Dec 10 18:48:01 CST 2003

Ralph is right.  From my recent research on this subject a properly functioning lead-acid (flooded or gel, sealed or not, standby or deep-cycle, most combinations possible) should show ~12.8v when fully charged (after resting for 2 hours) - this is the normal voltage of lead-acid chemistry with 6 cells.

It is safe to leave a 12.8v charger connected to these batteries since it can't push anything more into an already full unit.

Chargers tailored to 12v-nominal standby-use batteries (UPS, etc.) typically operate at ~13.8v.  This gives the extra push to speed up the charging and make sure that the battery reaches 100% charge.  Chargers tailored for deep-cycle batteries operate at higher voltages - as high as 14.7v.  The problem is that once your battery is fully charged with a higher voltage source, you need to disconnect it to avoid damaging the battery.  Many modern chargers will sense when the battery is full and then shut-off or switch to a 12.8v trickle charge mode.

The higher voltage charging helps push electrons deeper into the interstitial spaces between electrodes.  Deep-cycle batteries benefit from a bigger push because they are typically more electron depleted in the deep interstice.  This is obviously of greater concern in gel-cell batteries.  If you charge at only 12.8v the electrolyte abutting the electrodes will quickly charge to it's happy level and begin resisting current from the charger.  The charge will only slowly move deeper into the battery.  It's the same mechanism behind batteries charged at 14.5 temporarily showing higher voltages and temporarily shorted batteries initially show a depleted voltage, but then recovering.  I don't know the technical name - I don't think it's 100% synonymous with internal resistance, but I like to think of it as coulombic viscosity.

Karim
Self-Proclaimed Expert - Proceed with extreme skepticism ;)

-----Original Message-----
>From: dprglist-admin at dprg.org [mailto:dprglist-admin at dprg.org]On Behalf
Of Ralph Tenny
Sent: Monday, December 08, 2003 10:17 AM
To: 'Chuck McManis'; 'Earl Bollinger'; Karim Virani; dprglist at dprg.org
Subject: RE: [DPRG] Remedial Circuitry


Chuck:
I'll have to double-check; at age 72, my memory may not be what it once
was.
Meanwhile, what is the no-load (10k ohms/volt meter or better?) voltage
of 
one of your batteries about an hour after removing from the charger?
Ralph

-----Original Message-----
>From: dprglist-admin at dprg.org [mailto:dprglist-admin at dprg.org] On Behalf
Of Chuck McManis
Sent: Sunday, December 07, 2003 3:27 PM
To: Ralph Tenny; 'Earl Bollinger'; 'Karim Virani'; dprglist at dprg.org
Subject: RE: [DPRG] Remedial Circuitry

Did you really mean 12.8V Ralph or did you mean 13.8V ? My Lead/Acid 
chemistry charger keeps flooded batteries at 13.8 and deep cycle sealed 
batteries at 14.5V

--Chuck

At 03:05 PM 12/7/2003 -0600, Ralph Tenny wrote:
>One more addition to this thread! The most efficient charge for all
>Lead-acid batteries is to charge from a 12.8 v. source (for a nominal
>12 v. battery). As the battery approaches full charge, the charging
>current tapers off. Leaving the battery connected (float charging)
>replaces any normal self-discharge to keep the battery at full charge.
>Ralph
>
>
>-----Original Message-----
>From: dprglist-admin at dprg.org [mailto:dprglist-admin at dprg.org] On
Behalf
>Of Earl Bollinger
>Sent: Saturday, December 06, 2003 6:42 AM
>To: 'Karim Virani'; dprglist at dprg.org
>Subject: RE: [DPRG] Remedial Circuitry
>
>Well, that looks pretty good to me at this early in the morning.
>
>The resistor dividers should be setup for what you expect the maximum
no
>load voltage to be. But you may need to throw in some reverse biased
>Schottkey fast-switching diodes on the ADC input side to limit the back
>EMF that can be generated off the motors. This may be a problem if your
>ADC's have a problem with negative going voltage spikes. Some ADC's are
>0v to +Vcc and some ADC's can handle -Vdd to +Vcc voltages just fine.
>You need to check your ADC's specs on that. On some ADC's you might
have
>to use a ZENER diode to limit the maximum voltage a ADC could see, if
>the motors generate a lot of forward voltage spikes (such as braking in
>reverse). Some bypass caps may be needed to smooth out the voltage
>levels on the ADC inputs, to prevent the weird erratic readings being
>caused by the motors.
>
>Depending on the motors and motor controllers, the back EMF or RFI that
>could be generated, could cause some noise on the ground line that
could
>get into the computer system logic circuitry. Thus you might need to
put
>in a diode between the logic ground and the motor ground connection to
>help block the back EMF or RFI off the motors from getting into the
>logic circuits.
>If it is noisier, you might have to run a inductor-capacitor "PI" low
>pass filter on that common ground connection (like the ones in your car
>radio audio systems to filter the engine noises out of the audio
>system). Of course I think it's just us "old guys" anymore that
remember
>the loud motor whine coming out of the radio in the old days, with the
>car's engine running. I remember when my car was OK, but I could pick
up
>the "unfiltered" car next to me from several hundred yards away on my
>radio.
>The motor power system and the logic circuit system should only have a
>single common ground point of contact between the two. Usually the
motor
>system has the chassis ground and the logic system floats with only a
>single common ground point of contact. It does get interesting when the
>computer system requires a good shield or box of it's own, and you need
>to keep them separate from the chassis/motor ground.
>A lot of times that simple single common point of contact for ground is
>all that is needed to filter the noise out of the computer system. But
>if it doesn't then it's easy to add in filters as needed.
>
>I assume your using opto-isolators to isolate the motor system from the
>computer system. I have had motor controllers blow out on me in the
>past. Sometimes the motor controller blows out and allows high voltage
>to appear on the logic lines leading to the computer system, which is a
>definite bad thing to have happen. The computer fuse may pop right away
>but the high amp fuse on the motor side won't pop. Of course, debugging
>is easy, replace all the semiconductors and low voltage caps, reprogram
>and it' back up again. :(
>
>You can't go wrong having fuses in the system. These larger systems
>start to get downright dangerous. Especially at 3AM and your tired, and
>the probe slips or you drop that screwdriver or bolt, "oops". Of
course,
>it does really irritate you when you blow your last fuse at 5AM on a
>Sunday morning, and now you have to wait for the Radio Shack or Auto
>Parts store to open. I consider it to be very important to try and use
>common automotive type fuses (not the special electronics custom fuses)
>that you can get easily at auto parts stores or Radio Shack, et cetera.
>Although you can "kludge" up a temporary fuse out of many things, such
>as a strand of copper wire, you have to decide how important your
>computer system is if the temporary fuse doesn't pop if you have
another
>"oops". I almost forgot they just opened the new 24hr Walmart
>SuperCenter, about a mile from my home, they have automotive fuses too.
>:)  I'm saved.
>
>Isn't it interesting, how it always seems to take three fuses to pop
>before you realize there is something wrong?
>The first fuse pops, maybe it was an old one and went bad.
>The second one pops, humm, maybe it was a fluke.
>The third one pops, drats! Stupid %^#%#^#%#%#% darn #&#&#&#& infernal
>machine!
>
>
>
>-----Original Message-----
>From: dprglist-admin at dprg.org [mailto:dprglist-admin at dprg.org] On
Behalf
>Of Karim Virani
>Sent: Saturday, December 06, 2003 2:02 AM
>To: Tom Gralewicz; dprglist at dprg.org; Earl Bollinger; SOLID Corp.
>Subject: RE: [DPRG] Remedial Circuitry
>
>Thanks Robert, Scott, Earl, Tom and Ralph for your input.  I understand
>now  that reconnecting variously charged SLAs in parallel was the
>primary problem with my concept.  So I'm working from your various
>suggestions to plug 3 chargers into the existing circuit.  Also adding
a
>couple of voltage dividers to sense battery levels.  Please see the
>diagram (below) that I adapted from Scott's original.
>
>The chargers are all the harbor freight model that Tom pointed out.
>
>http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=45005
>
>I went ahead and bought 3 during the post-Thanksgiving sale at the
>Richardson store.  I'll be using them at the 2A setting.  The chargers
>plug into the "O" docking connectors.  From my research, cyclic
chargers
>are designed to put out around 14.7v, standby chargers less.  Assuming
>these are cyclic chargers (they don't specify their voltage output),
and
>rounding up, I'd expect a max of 15v from each charger.  When running
on
>batteries I'm interested in the region from 12.7v-fully charged to
>12.0v-emergency shutdown.  Thus the voltage divider values for level
>monitoring.  Do these calculations seem right?  I think I went in the
>right direction when figuring worst-case actual resistor values.
>
>How do I verify the actual voltage from these chargers before hand?
>They're supposed to autosense when to shutoff, and don't show a voltage
>when the circuit is open.  The manual says they need to detect at least
>.7v from the battery before attempting to charge.
>
>Assuming they shutoff on their own - I should be able to sense the drop
>to 12.8v in the ADC.  Can I have the ADCs monitoring while the chargers
>are active?  I don't know nuthin bout noise and filtering, etc.
>
>I didn't put much in the way of protection - these chargers are
supposed
>to be circuit-breaker protected.  Do I need more fuses?
>
>I don't understand why the diode is needed - I just copied it from
>Scott's diagram.  On a low battery it'll drop the voltage too much for
>the DC/DC converter down the line.  Can I drop it?
>
>
>       motor power
>             |
>            fuse
>      56k    |
>   +-/\/\/---+-------O
>   |         |       |              logic power (dc/dc converter)
>   |        -=-      +                  |
>   |        -=-   charger3             fuse
>   |        -=-      -                  |
>   |         |       |                  -
>   |         |       |                  ^
>   |-ADC.M   +-----O-+                  |  30k
>   |         |       |         O--------+-/\/\/--+
>   |         |       |         |        |        |
>   |        -=-      +         +       -=-       |
>   |        -=-   charger2  charger1   -=-       |--ADC.L
>   |        -=-      -         -       -=-       |
>   |         |       |         |        |        |
>   |         |       +---------+        |        |
>   |         |       |                  |        |
>   +-/\/\/---+-------O---------+--------+-/\/\/--+
>      10k    |                             13k
>           __|_
>           \ \ \
>
>I'd appreciate any further thoughts,
>
>Karim
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