[Oeva-list] OMEGA OL-750R Variable Load and Vicor Megapac miscellania...

Myles Twete matwete at comcast.net
Wed Feb 22 10:19:31 PST 2006

Hey OEVers-
I've been sitting on Gary Graunke's variable load (OL-750R by Omega) now for
about a year I think.
It's been of great use to me and I expect I can make good use of it thru
this Spring.
But if anyone on the list would really like or need the unit (I believe it's
a floating OEVA club tool...?), I'll hand it off to you.

Description: It's a box with 2 leads which can be connected to your
battery/charger/power supply and allows you to dial an increasing load and
observe the current (LED display) and a rough voltage indication
(interesting rotary LED bar display around the current readout).  By
adjusting the dials, you increase the current load on the
battery/charger/power supply and therefore can test regulation limits or
generate a load curve.

Specs: there aren't any...neither on the device, with it, or online
Observed performance:
        Voltage Range: Have tested to 72v, which is beyond the voltage LED
bargraph of 60-something
        Current Range: Have tested to 32amps, limited by the device's power
        Power Range: Have observed that power limits at
750watts---consistent with Model# 750R
        Set Point Reg: Unknown what is being set with the dials---just that
it adjusts the current draw.
        Displays: Current with multi-digit digital LED
                      Voltage with unique rotary bar graph around the
current LED
        Cooling: FAN
        Power: 110vAC

Test Examples:
1) Tested 36v bank of 4amp Vicor modupacs and confirmed 32amps delivered in
current limit...ie. voltage dropped to around 24v...36v bank was able to
deliver 21amps before POWER LIMIT reached.
2) Tested 72v bank of 5 - 200watt modupacs and observed only 10+amps
load----POWER LIMIT reached.

Today I'm fixing an IOTA 12v, 55amp charger and will see what the load do...

Anyway, this tool is very useful if you are building your own chargers (as I
have done) or want to characterize what you have.  You could for example
take a 12v, 70ah Hawker like I have and conceivably put nearly a steady 1C
load on it and see how long it goes before reaching the limit----too bad the
display doesn't toggle to voltage for detailed voltage readout...

To date I've now packed TWO 8-slot Megapacs with a combination of 24, 48 and
72v modules to yield 2 high efficiency CI/CV 2-phase chargers which can each
dish out between 11 and 13amps at 120vDC.  So together I can now recharge
the Hawker70ah batteries with at least 24amps (observed 28-30amps in current
limit while charging).  Most of the Vicor modupacs I rebuilt and
reconfigured from 2v/3.3v/5v/12v modules to 24, 48 or 72v modules.  Most
were also configured as booster modules instead of driver modules so they
could be paralleled.
Net Result: At least 2.5kw of 120v charging at a cost of approx. $130 thanks
to Ebay and a lucky day at local Portland surplus store 'R5D3' near Johnson
Creek.  The charger will work with 110/220vAC or a good range of DC input
power.  The chargers are 99%PFC and approx. 88-90% efficient overall.  Size
and weight of this charger set probably is comparable to a PFC30 and FAR
LESS than the 2 Lesters that came with my Milburn...I can also add
adjustability to the supply if I wanted to provide a wide range of voltage
and current.
Conceivably, for example, a single Megapac with 8 - 48v 4amp modules could
be configured to provide these outputs (limited by the 1.2kw spec'd for the
      24-53v: 32amps (one driver, 7 boosters...1 pot adjusts output)
    53-106v: 16amps (2 drivers, 6 boosters...1 dual pot for adjust)
   106-212v:  8amps (4 drivers, 4 boosters...2 dual pots)
   212-424v:  4amps ( 8 driver modules...4 dual pots...)
Driver DC/DC converters in modules can be made to act as Boosters...not
documented anywhere, but I've done it.

That's it for now.

-Myles Twete
matwete at comcast.net
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