Re: More Battery Recharging Questions
- From: Neon John <no@xxxxxxxxx>
- Date: Wed, 21 Dec 2005 23:47:19 -0500
On Thu, 22 Dec 2005 01:49:37 GMT, hchickpea@xxxxxxxxxxx wrote:
>On Wed, 21 Dec 2005 15:15:17 -0500, Neon John <no@xxxxxxxxx> wrote:
>
>>Golf Cart batteries tend to be fairly high impedance so the bulk phase
>>will end relatively quickly, usually around 50-60% of the total charge
>>required. Let's assume 60%.
>>
>>The bulk phase will take (130*.6)/40 = 2 hours. That will have
>>returned about 130*.6 = 78 ah.
>
>Whoa!!! Deep cycle batteries are not built like car batteries and do
>not like fast charging. Generally the recommended max rate of charge
>is a C/10 - C/20 is better. A C/10 charge for a 225aH set would be
>22.5 amps. A C/20 is about 11 amps.
>
>I didn't pay as much serious attention to this in the past as I do
>now, after pressing my system into use for the power outage from
>Hurricane Wilma. I had stuck the dip switches in the wrong position
>on my Trace smart inverter/charger when I added batteries, and charged
>at a much higher rate with my generator than I normally use.
I have no idea what wrong DIP switch settings did to your battery but
I know for certain that fast, intelligent charging does not harm these
batteries. I and many other EV owners prove that every day. I have a
72 volt, 70 amp charger on my EV that uses these same batteries and
they've been happily puttering along for over a year and a half now
with no loss in range. I installed a larger than stock charger. The
stock charger was 50 amps. I know more than one owner of my model EV
who is going on 7 years on his pack.
Further experience more directly applicable to RVing. I have two
Group 29 12 volt batteries in my MH. They're about 3 years old now. I
mostly dry-camp. The majority of the time they're charged at 150 amps
during the bulk phase by my CBC (cordless battery charger.) When
they're charged from shore power, the 60 amp PD Intellicharge/Charge
Wizard does the job.
These batteries have lost about a third of their capacity but NOT from
fast charging. They have about 250 cycles on them, many cycles below
80% DOD. Batteries are so cheap that I don't care much about overall
life. I have limited battery space and I want all the amp-hours I can
get out of that space. So I "abuse" them, at least by conventional
wisdom.
Fast charging will NOT warp plates, no more than fast discharging
will. OVER-fast charging, IE, fast dumb charging can cause plate
swelling if the over charging is excessive.
Trojan will tell you, if you call, get past sales to an engineer and
convince him that you a) know what you're doing and b) won't sue them
if you screw up, that their wet cell batteries suffer no life
degradation at C/2 charge rate with a smart charger and that an
initial rate of C is OK for a tightly controlled, temperature
compensated smart charger with programmable setpoints.
What damages wet cells is the formation of gas within the structure of
the plates at a rate faster than can recombine and diffuse out. During
the bulk phase, that is not a problem because the electrochemical
reactions are occurring on the surfaces of the plates. As the surface
conversion runs its course, the voltage rises as material deeper
inside the plates starts reacting. The reason for the voltage rise is
the added resistance of the electrolyte paths through the plate pores
and the reduced surface area available.
When the voltage reaches a specified point, selected so that plate
internal gas production isn't too great, the bulk phase ends, the
charger goes to voltage regulation and the absorption phase begins.
During this phase the current gradually drops as the reaction proceeds
deeper and deeper into the plates. When the current has dropped to a
fraction of the initial rate, the absorption phase is over, as most
material has been converted and most of the energy input is being
expended as heat and gas. The trickle phase begins at a lower
voltage, a voltage selected NOT to cause gassing. That stage finishes
off the last vestiges of sulfate.
All a higher bulk charge rate does is get through the bulk stage a
little faster. When the voltage rises to signify the end of the bulk
phase, the battery controls the charge rate from there one, as the
charger's voltage is now regulated.
If my smart charger could put 1000 amps into a golf cart battery, the
only result would be the practically immediate termination of the bulk
phase because of the voltage drop across the internal resistance of
the battery.
AGMs are much better. Hawker says that there is NO maximum charge
current for their Genesis line of AGMs. (There obviously is a limit
somewhere out there but Hawker isn't interested in debating semantics
with non-engineers.) Experience has shown that the Optima AGM also has
no limit. I know some guys involved in EV drag racing that are
discharging 55 AH Optimas at 2000+ amps, are dump-charging from a
larger, higher voltage bank at 500+ amps between heats and are on
their 3rd season with the pack.
John
---
John De Armond
See my website for my current email address
http://www.johngsbbq.com
Cleveland, Occupied TN
A foolish consistency is the hobgoblin of little minds.-Ralph Waldo Emerson
.
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