Wiring an hourmeter into a start circuit 1

[berkshire]

I am trying to wire an hourmeter into a 24volt start circuit on a motor. Since the hold in relay does not have an extra set of contacts. I would like to place this in series in the normally closed switch circuit ( the off switch.). The problem I hit was that the current draw of the hourmeter was not enough to keep the relay drawn in.
Would a light bulb work as a shunt or since this is an AC circuit would I be better off connecting a capacator across there. I guess what I am trying to achieve is a parallel circuit which gives the hourmeter enough current to work without starving the relay.

 

[Skogsgurra]

Would it not be possible to connect it in parallel to the relay coil? Most hour meters are "voltage devices" meaning that they shall have a voltage across them to run. Isn't there a name-plate saying what voltage it shall be connected to?

Gunnar Englund

http://www.gke.org

 

[berkshire]

Gunnar,
The hourmeter is, a voltage device it is 3 to 36 volts DC
I had wired a fullwave rectifier to it because the relay is working on 24volts AC.
I will see if I can get at the holding relay to do a parallel connection. This thing is buried under a massive contactor. It was of course much easier to get at the switch wires.
Thank you B.E.

 

[VEBill]

"...a fullwave rectifier..."

Does your fullwave rectifier circuit include a filter capacitor? There are many DC devices (most in fact) that do not like pulsating DC.

Also, a half-wave rectifier might provide a voltage not so close to the upper limit.

Might be cheaper to buy an hour meter that will operate directly from an available voltage.

 

[berkshire]

This hourmeter is an electro mechanical wheel type and is capable of working from the rectified output of an alternator.So I think that part of it will be ok.
If I do add a capacitor, will I also need a resistor in parallel with it?
B.E.

 

[VEBill]

"...need a resistor in parallel...?"

No, the meter itself (being permanently wired in parallel) should be adequate to provide the required parallel load.

If you decide not to use a parallel capacitor to smooth out the pulsating DC, then double check the hour meter to make sure that it is running at the correct speed. Pulsating DC can make things go 'hay-wire' (which is why it should be simply avoided to save time in the long run).

 

[berkshire]

Thank you VE1BLL,
I will go back and do battle again with this task today.
If I understand correctly what you are saying, the pulsating DC current may interfere with the crystal oscillator in the timer. Which is why it needs a smoothing condenser.
B.E.

 

[VEBill]

I thought it was (fully) "electro mechanical" (no electronics) and I was still concerned! If it contains electronics (like a crystal oscillator circuit) then forget about using pulsating DC. Don't do it.

Rule of thumb: nothing good ever happens with using pulsating DC power supplies.

 

[berkshire]

Ok you have talked me out of it. I will now go to plan B which is a 115volt ac hourmeter running off a stepdown transformer from the 480volt main supply.
Thank you for heading me off at the pass before I really screw up.
B.E.