Ampere sending unit

[Ken Murphy]

I am looking for a Dc ampere sending unit a 1990 marquis any help would be appreciated Thanks Ken Murphy

[Gerald Farris]

Ken,
I am not sure what you mean by ampere sending unit. If it is part of the instrumentation above the driver, we will need to wait for one of the early Marquis owners to answer, or you can call Beaver Coach Sales in Bend. However, if you are referring to the dash gauges, I think that they are standard VDO gauges that are available from any VDO distributor.

Gerald

[Ken Murphy]

Gerald,
It is for the panel above the driver’s area. It is a small box with a coil on it that the battery cable runs thru to show ampere draw for the coach. It is located in the rear engine compartment under the remote start panel. Thanks for the response

[Edward Buker]

Murph,

Usually the DC current measurement is made by looking at the voltage drop across a shunt resister that will handle high current. The value of the resister very low and is fixed. The measurement circuitry is calibrated such that the small voltage drop that is measered is translated to read out as DC Amps. There are some shunt examples if you try this link. You may be able to find some markings on the shunt like .1 ohms. The parts guys at Beaver Coach Sales may know what the part is and possibly  help you find one. Hope this helps.

http://www.rc-electronics-usa.com/current-shunt.html

Later Ed

[Ken Murphy]

Ed,
The panel works by voltage the unit has three wires the red white and black. The black is a chassis ground the red is an input and the white is the output. The panel sends 8 volts to the unit thru the red and voltage is returned thru the white. At 0 amps the voltage on the white wire is 4 volts. If the output voltage is higher on the white wire and the panel will read a + ampere value if voltage is lower then 4 volts and the panel read a - ampere value. I am out of town now when I get home Monday I will post a picture of the unit. Thanks    

[Edward Buker]

Ken,

Usually if current is to be measured in both directions you would use a dual shunt as shown in this link which would have 3 wires.

http://www.sogeman.com/DC+DMM_install.pdf

By your description it sounds like this is an active circuit of some kind and not a traditional shunt. One way to know if it is a shunt, it will have relatively large cables to deliver the current through the shunt and smaller sense wire terminals for the voltage sense wires.  In the case of the shunt you would have very low voltages and not what you describe.

 It sounds like you might have a torroidal transformer (shaped like a donut) acting as an inductive pickup for current flow in the larger battery chassis wire which would pass through the center of the torroid. Then maybe some kind of active sensing circuit is involved at the panel. This arrangement is usually just used for sensing on AC lines because the torroid needs some changing fields to induce voltage as a pick up.  If this is the kind of sensing arrangement that you have there would only be small wires going to the torroid and no large cable connections are involved at all. If it is a torroid and it has failed (open on one leg) you may be able to measure the remaining leg and sort out the configurtion and order one. Hope this shot in the dark helps.

Later Ed