[EVDL List]

Once upon a time, someone mentioned to me that the E-meter pre-scaler
was just a resistor divider. These days, it seems Xantrex doesn't
even sell one for the LinkPRO. It seems to me like one would be
pretty easy to build, provided I knew the following:

1) What is the input impedance of the meter?
2) Does the divider need a filter capacitor, i.e. does the signal go
directly into a sample-and-hold circuit that needs low input impedance?
3) Has anyone else already solved these problems who is willing to
share?

Can anyone offer any help?

Thanks!
-Ben

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[EVDL List]

Here is the "How to" post from Lee Hart in 2006

>The precise value for the 500v prescaler is 1057k. Note that a normal 1%
>1/4w metal film resistor has a 250v maximum voltage rating, so you
>should use two resistors of half the value in series for a 500v
>prescaler if it will actually see ove 250v. The 100v prescaler has a
>118k series resistor.
>

>Cor van de Water wrote:
> > Correct, a zener diode is a good addition to avoid higher voltages
> > into the Emeter than it can sustain. Maximum should be a 50V zener
> > diode. This will not blow the fuse, but increase the current through
> > the HV resistor, to drop more voltage if the input goes over 500V
> > (which it better not does, or the HV resistor may get out of its
> > own spec, when you use a 500V resistor the input MUST not go over
> > 550V as you are dropping 500V over the HV resistor and 50V over the
> > zener in parallel with the potmeter)
>
>The Cruising Equipment / Heart / Xantrex prescaler has a 50v zener not
>to protect the E-meter, but to protect the installer from shocks while
>connecting the wires to the E-meter.
>
>A plain old neon lamp (without the resistor; the prescaler resistor
>takes its place) works better than the zener. Zeners still draw current
>even below their zener breakdown voltage; this causes a slight error.
>Neon lamps are a totally open circuit until you reach their breakdown
>threshold of about 50-60v. The E-meter has enough internal protection to
>handle this slight overvoltage.



At 10:34 PM 8/29/2010, you wrote:
>Once upon a time, someone mentioned to me that the E-meter pre-scaler
>was just a resistor divider. These days, it seems Xantrex doesn't
>even sell one for the LinkPRO. It seems to me like one would be
>pretty easy to build, provided I knew the following:
>
>1) What is the input impedance of the meter?
>2) Does the divider need a filter capacitor, i.e. does the signal go
>directly into a sample-and-hold circuit that needs low input impedance?
>3) Has anyone else already solved these problems who is willing to
>share?
>
>Can anyone offer any help?
>
>Thanks!
>-Ben
>
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[EVDL List]

Ben Apollonio wrote:
> Once upon a time, someone mentioned to me that the E-meter pre-scaler
> was just a resistor divider. These days, it seems Xantrex doesn't
> even sell one for the LinkPRO. It seems to me like one would be

Belktronic sells one:
http://www.belktronix.com/LinkProAdapter.html

I have been very pleased with my Belktronic purchases.

BTW, the LinkPro seems to be a re-branded TBS.

--
Willie, ONWARD! Through the fog!
http://counter.li.org Linux registered user #228836 since 1995
Debian3.1/GNU/Linux system uptime 171 days 23 hours 33 minutes

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[EVDL List]

Ben Apollonio wrote:
>
> Once upon a time, someone mentioned to me that the E-meter pre-scaler
> was just a resistor divider. These days, it seems Xantrex doesn't
> even sell one for the LinkPRO. It seems to me like one would be
> pretty easy to build, provided I knew the following:
> ...
>

Instructions on how to make a 1:10 prescaler for the TBS Xpert Pro (same as
the Xantrex Link Pro, I believe) are here:
http://www.tbs-electronics.nl/downloads/epro_passive_1-10_prescaler.pdf

Briefly, you need a 12V to 12V isolated DC-DC converter to safely power the
gauge's +/- terminals from the vehicle's battery. You need a 436.5k resistor
in series with the Vm input (best composed from 2 x 200k and 1 x 36.5k
resistors in series, all 1% - do not use trimpots here) followed by a 0.1uF
capacitor in shunt across the gauge's Vm and - terminals to filter noise
(value not critical, but don't omit).

Then you just have to set the gauge to scale the input by 10 and voilla.

I've built this on perfboard a couple times before, but if enough other
people are interested I'll have a pc board made...


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