Paul Wallace wrote:
Lee, the [main] DC/DC is connected to an always hot 12vdc source in the
power distribution block in the truck... it's a Ford/Lambda unit from the
old Ford Ranger EV program, good for 100amps from 180v to 385v input and
backed up with four 10ah headway cells in series so I don' think I have
fading problems with the 12v input to the emeter DC/DC.
OK; that all sounds solid.
The emeter DC/DC is a Datel UWR-12/250-D12 isolated 12v (9v to 18v
input range) to 12v converter good for 250ma max and with an output
regulation of 0.5%.
That's the part number that Cruising Equipment and Heart Interface used.
It is supposed to be good for up to 250ma, and the E-meter / Link-10 is
supposed to draw no more than 250ma.
The emeter seems to have the internal EV filter. There is a very
large electrolytic cap stuck to the top of the controller IC with
foam tape that looks like the 1000uf 35vdc part you describe.
Yes, that's the "EV filter". Your meter has it.
I think that the problem may be the DC/DC converter itself. When I
measure its output voltage with the Emeter display sleeping, only the
bar graph lit, and with a flashlight on the light sensor, I read an
input voltage to the emeter of 11.1vdc. If I wake up the display,
the digits showing 333 (traction voltage), the input to the emeter
falls to 10.2vdc. Looks to me as if the emeter DC/DC can't supply
enough current to drive the emeter, or it is failing.
It sure sounds like the DC/DC is the problem. I would certainly expect
it to deliver 12v with the E-meter sleeping.
However, there is another possibility. I've been selling the EV
Companion for years (www.sunrise-ev.com/LeesEVs.htm about the middle of
the page). It uses an isolated DC/DC similar to the Datel part. I've had
reports that *some* E-meters draw more than the specified 250ma. None of
my E-meters do, so I haven't been able to investigate what was changed
inside that might account for this. Maybe they did something to increase
display brightness, or switch part vendors, etc.
Anyway, when this happens the DC/DC can be overloaded. Its voltage sags.
The switchmode regulator inside the E-meter tries to compensate by
drawing *more* current at the reduced voltage. This overloads the
external DC/DC even more, etc. The result is that the E-meter
momentarily loses power, and resets. This reduces the power, so the
DC/DC comes back on, the E-meter starts working again, and you have no
idea what happened.
A crude "fix" for this is to put a little piece of dark tape or a felt
pen mark on the light sensor on the front of the E-meter. It will think
it's dark, and so reduce the LED brightness. This lowers the supply
current so it won't reset. The light sensor is a tiny dot between the
"A" and "Ah" indicator lights.
Try this, and see if the resets go away. If not, then replace the DC/DC
converter.
--
If you're not stubborn, you'll give up on experiments too soon.
And if you're not flexible, you'll pound your head against the wall
and not see a different solution to a problem you're trying to solve.
-- Jeff Bezos (founder of Amazon.com)
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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