Michael Ross wrote:
my power supply allows me to tell it a peak current and peak voltage...
It sounds like I can safely set the voltage to 28.8V and 4 amps, and
not be concerned if I forget for a few days. Do I have that right?
What is the amphour capacity of your batteries? 28.2v and 4a is OK for
maybe a day, but not for days. At 28.2v, plug the power supply into a
timer and set it to shut off in 16 hours or so.
If you have to leave it on for days, set the voltage for no more than
27.4v (13.7v per 12v battery). That is a relatively safe long-term voltage.
If I am in a hurry, I could wait for 28.8V, then perhaps set it a 30V and
1Amp?
30v and 1 amp max is OK for an hour or two at the most. That will
equalize the batteries.
It all depends on how much babysitting you want to do. Probably the
simplest way is to get one of those 12-hour timers that install in a
light switch box, normally used to control a bathroom fan or outdoor
yard light. For example, an Intermatic FF12HC etc.
http://www.intermatic.com/Products/Timers/InWallTimers/Springwound_Auto-Off_Timers/FFCommercialSeries/FF12HC.aspx
To charge:
- Plug your power supply into the timer.
- Set the timer for 12 hours.
- Set the power supply for 28.8v and its maximum current.
- Wait for it to shut off. The batteries are approximately 100% SOC.
To equalize:
- Charge as above. Then...
- Set the timer for 1 hour.
- Set the power supply for 30v and a maximum current of 2% of the
battery's amphour rating (i.e. 0.4 amps for 20 amphour batteries).
- Wait for it to shut off.
I could rig up a JLD 612 temperature controller to be a minder and shut off
the charge at 100F or so.
When a sealed battery gasses, it heats up and pressurizes the case. If
it charges too long, or at too high a current, it blows the vents open,
and loses water. That's bad for life.
The heat also shortens the battery's life. As temperature rises, the
battery voltage falls. This makes it draw more current, which causes
more heating... This is called "thermal runaway", and leads to
destroying the battery. A good charger has temperature compensation to
detect the temperature rise, and turn down the voltage or shuts off to
prevent this.
I could also mange it for temperature and use a plain old 10A 12V charger
with the cell paralleled. Does this idea have merit/
If that "plain old 12v charger" is any good. Many of them are nothing
but a transformer and rectifier in a box. No voltage, current, or time
control at all.
--
If we knew what we were doing, it wouldn't be called research, would it?
-- Albert Einstein
--
Lee Hart's EV projects are at http://www.sunrise-ev.com/LeesEVs.htm
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