HI Mac;
I don't think the generators will be overloaded. i may be wrong, but I
believe they will just put out what they can, and the batteries will
slowly come up in voltage. I have a large fork lift battery charger
that is essentially unregulated, and it never has been overloaded. It
will definitely over charge the batteries if left on too long, however.
The dead batteries are not going to act like a short circuit, they will
have quite a bit of internal resistance that will limit the total
current flow when charging. Again, you didn't mention the brand or type
of generator, so I can't say if I have experience with it, so this is
just my uninformed 0.02 worth.
Ray Walters
Remote Solar
On 1/28/18 8:23 PM, Mac Lewis wrote:
Hello wrenches,
I'm working on 3 off-grid telecom sites. They are designed to operate
solar only under most conditions but the project manager ordered a
custom-built 48 VDC generators, intended to be used as the battery
charger/backup power for the site. These are ~20 kW generators, and
can probably do about ~350Adc at 48 Vdc at the elevation that these
are sited. The battery banks are 4 x 1000 Ahr GS Nanocarbon 48
battery strings and can gobble up the 350Adc easily when they are
discharged.
While discussing the generator operation with the generator supplier,
we have found this generator isn't capable of charge control, or
limiting its own output. The charge control functionality isn't
necessary at this site because we really just need it to keep things
online until the sun returns, a simple 54 VDC float voltage would
work. However, without the generator being able to self-limit its
output, we expect this generator to stall when started because it
can't regulate its output current and will immediately become
overloaded by the discharged batteries.
I am trying to come up with some options to rectify this serious
design issue. One idea that immediately came to mind was putting in
some parallel solar charge controllers between the DC generator output
and the battery bank. If the generator output could be dialed up to
around 60-70 VDC, could parallel solar charge controllers be used for
charge regulation? It would be kind of like charging a 48 V battery
bank from a 70 V battery bank. MPPT isn't applicable, could the max
current limit in the charge controller(s) be used to regulate charge
rate? Will the charge controllers blow up? If not, what brand might
work. Each site has 8 x Midnite Classic 150s but I'm open to other
manufacturers if it would work. I am open to blowing up a charge
controller in the shop but I thought it best to ask first.
What are other ways to put this generator to use, and limit its load?
Thanks for your input/comments
--
Mac Lewis
*
"Yo solo sé que no sé nada." -Sócrates
*
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