Re: More Battery Recharging Questions
- From: Neon John <no@xxxxxxxxx>
- Date: Wed, 21 Dec 2005 15:15:17 -0500
On Wed, 21 Dec 2005 11:45:57 -0800, rvfulltime
<rvfulltime@xxxxxxxxxxxxxxxxx> wrote:
>I'm still trying to learn the best way to recharge my HitchHiker batteries while
>dry camping. I have a new Yamaha EF1000isc generator, 1000 peak
>watts. I stopped into Wal-Mart today and saw a single Black & Decker
>25/10/2 amp charger for $68. Since my generator only puts out 8amp
>on the 12volt DC outlet, I suspect that the charger may be a lot faster.
>I also read the manual that Nu-Wa provided regarding the built-in
>charger, and it was pretty useless.
I believe that charger is "only" a 10 amp charger. You may want to
check another Walmart. The one here has the full line of Vector/B&D
including the 40 amp one.
In general you want to get the highest amperage smart charger you can
afford so as to minimize your generator run time, consistent with your
generator's capacity, of course. If your generator is 1000 watts, and
assuming 90% efficiency in the charger, that's 900 watts to the
battery. 900/14= 64 amps. Your generator should be able to run a
high power factor 60 amp charger. A 40 amp low PF charger such as the
Progressive Dynamics unit is about that limit.
If you have golf cart batteries (225ah usually) and run them half
down, the charging will look like this. You need to return about
110ah to the batteries. These batteries have a Charge Efficiency of
about 85% so that means the charger will need to supply 110/0.85 = 130
ah. At 40 amps charging, the first order approximation will be 130/40
= 3.25 hours.
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. The next stage, the absorption stage
requires 3-4 hours for wet batteries regardless of the capacity in the
sizes we deal with. The amp rate tapers fairly linearly over the
absorption stage. The usual termination of the absorption stage is
defined as the point where the current drops to about 2% of the
initial rate (the bulk rate.)
I recommend running at least an hour in the absorption stage. This is
mainly to preserve the life of the batteries, as they will gradually
hard sulfate if left significantly discharged over a long period of
time.
So you're looking at around 3 hours of generator run time for
discharges in the 50% range. Less discharge will shorten the bulk
phase but have little impact on the absorption phase.
For lower amperage chargers, the bulk time stretches out
proportionally. The absorption phase will be affected some but not as
much.
When you reach shore power it is important to allow the full charge
cycle to complete, as this clears out nascant hard sulfate crystals
that will eventually grow to clock the plates' pores and kill the
battery. If you don't get to shore power for an extended period, I'd
do a complete charge every 4 or 5 cycles.
>
>I'm going to be doing about 6 or 7 nights of dry camping soon. So now
>I have a few more questions:
>
>1. How do I know when the batteries are charged? I know that the best
>way is to use an hydrometer(?) on each cell and if that's not available to
>use a voltmeter, but that can measure a surface charge. If I use the 12 volt
>DC outlet to recharge the batteries, how do I know when to disconnect
>the batteries from the charger?
The smart charger will take care of that. It runs through the
complete cycle and then returns to standby. The Vector/B&D displays
"FUL" when charging is complete. The Schumacher chargers display
"100"% charged and the amperage LED returns to the top. I don't
recommend the Schumacher charger (The "other" walmart smart charger)
for generator use because the power factor correcting circuitry is
very sensitive to frequency. It is very easy to let the blue smoke
out. I've done it to two of 'em now. An inverter generator might be
safe if the frequency is dead-nuts on 60hz.
Unless you've completed an equalization cycle with vigorous bubbling,
the SG will lag several hours behind the actual charge because it
takes that long for the liberated acid to diffuse out from between the
plates. I have a hydrometer but franky, I haven't touched it since
I've had my smart chargers. I just let the charger run to completion
and then turn it off.
>
>2. Do I need to disconnect the batteries from the trailer when recharging
>them?
Usually no. If your charger has an equalization cycle, the voltage
could reach as high as 16 volts which will drastically shorten the
life of the incandescent lamps. You can either turn the lights off or
hit the main disconnect if you have one. No need to unhook the
batteries.
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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