Tacho and Temp Instruments

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Chris King
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Tacho and Temp Instruments

Postby Chris King » Mon Jul 12, 2010 7:54 pm

Help on two issues please

The first is I wish to be able to read the RPM of my DC Brushed motor and seeking the best way to connect this to a tachometer on the dashboard.

The second is I wish to have a temperature guage on the dashboard to show the state of the electric motor whilst testing and in general use.

Keeping it simple - What instruments and connections are available 'off the shelf'?

Chris King

Chris King
Posts: 27
Joined: Thu Sep 18, 2008 6:58 pm

Re: Tacho and Temp Instruments

Postby Chris King » Wed Jul 14, 2010 8:00 pm

At last I have found a company that has sensors that can be used as a sender unit to a tachometer fitted on the dash; www.etbinstruments.com were helpful and gave me the guidance needed. I will let you know how it works and also the temperature gauge I will also be fitting in due course.

Best wishes - Chris

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ChrisB
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Re: Tacho and Temp Instruments

Postby ChrisB » Thu Jul 15, 2010 6:00 pm

Well found Chris

I've used VDO stuff before on my Beach buggy and have been pleased with the result.

ChrisB
I reject reality and substitute my own !!!!!!

Chris King
Posts: 27
Joined: Thu Sep 18, 2008 6:58 pm

Re: Tacho and Temp Instruments

Postby Chris King » Thu Jul 15, 2010 7:30 pm

Thanks for that - I am expecting the VDO tacho and temp instruments - with the appropriate sensors to arrive tomorrow, so hope to start fiting them this weekend. The tacho sensor will work from my gearbox flywheel, which will need two small projecting ferous bumps (bolt head or nut).

Just out of interest, what is the max RPM you run your motor - and did you add a temperature guage? I have to adjust the DC brush set, as at the moment it is set in the neutral position having come from a forklift truck. The forklift went backward as much as it went forward - hence the neutral position, but I will be using the motor in one direction only connected to a gearbox. I understand the setting is done by trial and error - but the tacho and temp guages will make it much easier to monitor its performance.

Will let you know how it goes in due course. Best wishes - Chris

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ChrisB
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Re: Tacho and Temp Instruments

Postby ChrisB » Fri Jul 16, 2010 9:14 pm

Ah sorry forgot to mention that the buggy is powered by a 3.5 Rover V8 :oops: :lol: :lol:

So its driven off the signal from the points.

Watch out if your adding anything to the flywheel as it could unbalance it and you'll end up with a vibration which could do for things like gearbox/motor bearings over time.

ChrisB
I reject reality and substitute my own !!!!!!

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Night Train
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Re: Tacho and Temp Instruments

Postby Night Train » Fri Jul 16, 2010 9:29 pm

Generally a tacho will work from the pulse from the distributor so you could set up a magnetic pick up to measure the rpm. Set to a 4 cylinder ICE it will require two pulses per revolution. One way to do this is to have two bumps or two flat spots or holes set at 180deg apart on the flywheel, or better on the motor tail shaft if there is one, that the magnetic pick up will pulse from.

It is better on the shaft, at either end of the motor, as any minor descrepancies in mass will have less effect on the balance if it is close to the axis then if it is on the edge of the flywheel.

I know of one chap who just stuck two neodymium disc magnets on the end face of his tail shaft. The sensor picked up on the outer end of the magnets as they rotated round. Being on the end of the shaft and close together it didn't affect the balance and the magnetic force was enough to keep them there.


I have also had it suggested that it is advantageous to get a tacho with a shift light. The shift light can be set to illuminate at any rpm to indicate that a gear change is needed. With an EV you set it to just under the safe maximum motor rpm and then use the lamp circuit to trigger the 'no throttle' or 'brake cut out' on the controller. That way if the motor ever tries to run away, say you forgot to put it in gear, then it will kill the controller before the motor spins itself to death.

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ChrisB
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Re: Tacho and Temp Instruments

Postby ChrisB » Fri Jul 16, 2010 9:34 pm

Clever couple of ideas there night train 8)

ChrisB
I reject reality and substitute my own !!!!!!

Chris King
Posts: 27
Joined: Thu Sep 18, 2008 6:58 pm

Re: Tacho and Temp Instruments

Postby Chris King » Sat Jul 17, 2010 7:50 pm

Thanks Guys

The V8 did not surprise me as much as the thought of a Beach Buggy being powered by an electric motor - now there is an idea! My project is a Pembleton Kit Car www.pembleton.co.uk (2CV bits on a light frame) being powered by a forklift truck motor (45kg 24 volt DC Brushed motor).

The man at www.etbinstruments.com was very helpful explaing the choices of installation. I am going for sticking two very small magnets - one each side of the flywheel so that two pulses are picked up each revolution (this is apparently the equilavent of a 4 cylinder ICE which the tacho understands and explained by Night Train). Anyway these very small magnets stick like glue to the ferous flywheel but are then given a drop or two of epoxy resin to ensure a good fixture. As they oppose each other the balance is not affected.

The sensor is then positioned a couple of mm distance from the revolving magnets by simple adjustments. I have done this today and will try to fit the tacho and cable tomorrow.

Thank again for the suggestions and comments.

Chris King


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