There's really no guessing involved here, as you might suspect. Batteries
have optimum maximum and minimum charge specs. Wet cells are 2.2ish volts per
cell (it'll be on the charge recommendation sheet or MSDS or something) and
minimum is 1.75 per cell(the best I can recall offhand). Meaning, at max
charge, a 36volt system ought to be reading about 39-40 volts, and when
depleted, will read about 32. These voltages will be "under load". As someone
mentioned, volts will creep back up a little if the batteries are left for a
bit, as some residual chemical action always takes place, but there isn't much
depth to that kind of thing, and the power depletes quickly. Also, with wet
cells, there is a risk of reverse polarity issues (pole swapping) once you go
below the minimum recommended voltage, especially with strings of batteries
and high draw systems like ours. These numbers can be monitored on a simple
voltmeter (or a volt-ohm meter in circuit, which is simpler if you don'! t
have something designed in). Just run the batteries down to 32ish, in your
case, planning to be done for the day at just about that time, and you should
be fine. I'll have to admit, it didn't even occur to me that people were
diving WITHOUT some way to monitor batteries!!! It's too much like flying
small airplanes without a gas gauge, in my mind, only you don't get to look
for an open field to land on.
Vance
-----Original
Message-----
From: Dan. H. <jumachine@comcast.net>
To:
personal_submersibles@psubs.org
Sent: Mon, 15 Oct 2007 7:58 am
Subject:
Re: [PSUBS-MAILIST] battery charge level
Brian,
This a VERY good question!
I have a sub and don't have a
handle on it. I have a small digital volt meter wired in, so I can monitor
either of my three battery systems, one 24V two 36V. The voltage varies quite
a lot depending on the usage. After using it and when there is no current
draw, the voltage keeps climbing back up, and what it go up to seems to depend
on how long the load had been turned off. I don't find much stability in the
voltage. When the batteries are almost totally depleted, there is a noticeable
reduction in prop speed, but by then there isn't much
left.
Just to be safe, my sub is wired where I can switch
between the two 36V pods. They are both used during a dive but on always runs
out before the other. When either runs out, it's time to quit for the
day.
The same problem when charging. It's a guessing game
when the batteries are totally charged.
If anyone has a way
to monitor, I'd be grateful to here it.
Thanks, Dan
H.
----- Original Message ----- From: "Brian Cox" <
ojaivalleybeefarm@dslextreme.com>
To:
"Personal_Submersibles@Psubs. Org" <
personal_submersibles@psubs.org>
Sent:
Monday, October 15, 2007 1:28 AM
Subject: [PSUBS-MAILIST] battery
charge level
> Ok, this is a stupid question but it has
been bugging me.
> How do you know how much charge you have in
your batteries? > Other
> than keeping track of how long you
have run your motors how can you tell.
> I know that the wwII subs
would have to check the battery acid levels to
> accurately know
how much power was in the batteries. But with the sealed
> AGM or
gel batteries you can't measure the acid, and chances are you
>
wouldn't be able to anyway in a small sub.
>
>
Thanks,
>
> Brian
Cox
>
>
>
>
>
>
>
>
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