[RE-wrenches] Off-grid non-inverter battery charger recommendations?

William Dorsett wmdorsett at sbcglobal.net
Mon Oct 15 19:32:01 PDT 2012


Good answer, Mick. I've got an old Trace DR 1512 with charger, and these
people have a very small inverter plugged into a wall outlet (old cigar plug
wall outlets were max'd at 60watts). So they don't do much with it but might
want some ability to run AC loads. I'd sell it to them cheap and they might
be able to equalize the batteries. Need to check the max voltage output. As
always great input, thanks for all your thoughts.

 

Bill Dorsett

Sunwrights

Manhattan, KS

 

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Mick Abraham
Sent: Monday, October 15, 2012 12:27 PM
To: RE-wrenches
Subject: [RE-wrenches] Off-grid non-inverter battery charger
recommendations?

 

Hi, Mechanix~

Bill Dorsett polled the group about recommended battery chargers for
connection to a generator. Iota brand is the successor to Todd brand; I
believe Iota bought the designs, tooling, etc. and these have appeal because
of the relatively low cost per rated amp. They seem generator tolerant.

The Todd design is a "constant voltage" type charger, however--basically an
AC to DC converter with a fixed voltage output. In my experience, the "75
amp" Todd type charger will deliver 75 amps only for a relatively short time
when first connected to a low battery. As the battery's voltage comes up
that presents a sort of "back pressure" which slows the rate of charge.
That's not so bad if one has utility power >always on< to drive the charger,
but if an engine generator is running...

The inverter/chargers (with which we are all familiar) begin with a
"constant current" part of the charge cycle--aka bulk charge. The charger is
determined to sock the battery with the amperage we have requested in the
setup; I think a pulse width modulation is going on where the charger hums
up its voltage in order to keep the amps high even as the back pressure
builds. When it's time for the absorption phase of the charge, the logic
shifts to a "constant voltage" where the amps are gradually dialed lower in
order to keep the battery at the target voltage so it can "absorb". Ignoring
the float phase which would come later, this overall charge regimen would be
called CC/CV for "constant current/constant voltage". The CV part of that is
not much different from what a Todd style charger does; it's just that the
Todd design does not precede that phase with a CC "constant current" phase. 

Some free-standing battery chargers have a CC/CV algorithm but those seem to
cost as much or more than a comparably rated inverter/charger. Check the
Magnum mod-square multi's, Bill, such as their RD series. As others on this
List have noted, just the charge function is pretty good and since the
inverter circuit is not pure sine, that keeps the cost lower. Built in time
delay before it loads up the generator is an added benefit. 

Jolliness,

Mick Abraham, Proprietor
www.abrahamsolar.com

Voice: 970-731-4675

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