# Tachometer into a voltmeter, gas gauge into an amp counter



## PThompson509 (Jul 9, 2009)

Hiya,

Not sure I can do it in laymans terms, but I'll try.

Most tachometers are driven by a series of pulses, and most gas gauges are driven by a certain amount of current. So, with an embedded computer, you can have that computer listen for the number of amps that are passing through your main battery cable. From that, you can keep track of how many amp-hours are left in your pack (state of charge). So with this info, you can now have that embedded computer drive the gas gauge and also the tachometer.

This is basically what I'm trying to do now - but my gas gauge is so old (1975) that it doesn't really behave.

Cheers,
Peter


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## Ivansgarage (Sep 3, 2011)

Looky here, Fuel gauge driver...

http://www.evworks.com.au/index.php?product=INS-ZEVA-FGD11

this one will work the tach
http://www.evworks.com.au/index.php?product=INS-ZEVA-FGDP



1999 sonoma electric
http://ivanbennett.com/


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## dtbaker (Jan 5, 2008)

INSURANCE GUY said:


> Need the experts to help me utilize my dashboard tach as an anmeter and the gas gauge as an amp counter. I have the connections, who can explain to a layman best way to use these. Thanks


leave the tach a tach, and just get an evDisplay to mount on the dash.... a mere $200 for the hall effect end and the gauge included will save you endless hours of frustration trying to make your gas gauge show anything with any accuracy.


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## dataman19 (Oct 7, 2009)

Wait a minute...
Since when are "gas Gauges" accurate?
They only show there is or isn't gasoline in the tank.
Their accuracy is debatable.
Our Hyundai Accent shows a full tank up until there is 6 gallons in the 11-galklon tank, then it slowly decreases down to zero at about 1.6 gallons in the tank (I know this - I Ran it dry once, Hard to do in a car that gets 35-39MPG - but I did.)
..
The Ford F-150 shows full until you use 4 gallons of gas. It shows empty when you have about a cup of gas (so you defenitely need to fill it up.
..
The EV (another Hyundai Accent) shows empty all the time - maybe it's because I don't have the gas gauge connected. EVs don't run on gasoline, so I don't see a need for the gas gauge to work.
..
The tach has been modified (electronically) to show motor RPM and has a switch to show wheel RPM. There is a digital battery monitor embedded in the Tach (hence no need for a battery modified gas gauge).
..
The speedometer works just fine.
...
But the Fuel Gauge and Tach adapters are cool.
..
But I like driving the EV Accent, it is just fun.
...
Dave
Phoenix, AZ


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## ruckus (Apr 15, 2009)

Ivansgarage said:


> Looky here, Fuel gauge driver...
> 
> http://www.evworks.com.au/index.php?product=INS-ZEVA-FGD11
> 
> ...


I have the Zeva fuel gauge with tach-to-amps driver. Found a nice little 10,000rpm tach (for 1000Amps) that will be the amp guage in the dash. An analogue gauge is way better than digital for a rapidly changing display. The digital will just spit out rapidly changing unreadable garble that looks like '888', but the analogue gauge will show a nice sweep of the needle. Of course, once you are using steady amps, the digital gauge has better accuracy... 

Ordering the tach right now, so don't have it all hooked up yet... Will post how it works.

As for the fuel gauge.. The manual says it is adjustable up to 200ah batts. Well the Jag has 260AH Thundersky so it looks like it will read 'empty' a bit early. That is fine. It will be like having a large 'reserve' tank.

Cheers


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## dladd (Jun 1, 2011)

ruckus said:


> An analogue gauge is way better than digital for a rapidly changing display. The digital will just spit out rapidly changing unreadable garble that looks like '888', but the analogue gauge will show a nice sweep of the needle. Of course, once you are using steady amps, the digital gauge has better accuracy...


fwiw, I have the EVDisplay with the bluetooth sender going to my Android on the dashboard, and I have both an analog and digital readout for battery amps showing. I have no problems reading the digital gauge, in fact I tend to look at it first, especially if I am trying to see exactly how many amps I'm putting out. The analog is fine, but it's pretty hard to tell 120a from 140a (my typical usage at around 65mph), where the digital is easy. Anyway, even under hard acceleration the digital gauge is not just a blur. Not sure what digital gauge you're using that looks like '888', but I've certainly never seen that with the EVDisplay unit.

I don't yet have mine wired to the stock fuel gauge, but I do plan to do that at some point. For now, I only know my 'fuel' level if I have my DroidX on the dash. My factory tachometer is used as a tachometer. Just cause it's electric doesn't mean I don't need to know how fast my motor is spinning!


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## ruckus (Apr 15, 2009)

Glad you are having good results. Sounds like your instrumentation is working very well. What is the data acquiring mechanism? 

My experience with having trouble reading digital outputs during fluctuation is from volt meters and those silly digital gauges in the 80's cars. I agree the accuracy is better once they settle down.

Yes, the vehicle still has the 'original' Classic Instruments tach. The mini tach/amps guage is going to replace oil pressure or some such unneeded ice gauge. Despite the lower accuracy, analogue LOOKS right in a 37 Jaguar dash.

Don't really need an amps guage, just adds a bit of fun-factor.

Cheers


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## dladd (Jun 1, 2011)

ruckus said:


> Glad you are having good results. Sounds like your instrumentation is working very well. What is the data acquiring mechanism?


I know it uses a Hall effect sensor, beyond that I have no idea. I'm strictly a plug and play end user... It's the EVDisplay made by Dimitri, sold by emotorwerks.com for use with an Android device (tablet/phone).



> My experience with having trouble reading digital outputs during fluctuation is from volt meters and those silly digital gauges in the 80's cars. I agree the accuracy is better once they settle down.
> 
> Yes, the vehicle still has the 'original' Classic Instruments tach. The mini tach/amps guage is going to replace oil pressure or some such unneeded ice gauge. Despite the lower accuracy, analogue LOOKS right in a 37 Jaguar dash.
> 
> ...


That's actually one of the things I like about the emotorwerks version of the EVDisplay, no mods to the dash. You just mount an android tablet (or phone) on the dash in whatever way you like. In my case, it's just a portable beanbag style holder. I agree on not needing the amps gauge, it's fun at first but once I got a feel for the car I don't really need it. The state of charge is the important one, especially when doing partial charges during the day (which I do quite a bit). However it is nice to have amps/volts/SOC available when wanted.

once I get the EVDisplay set up to drive the stock fuel gauge, I probably won't even bother to pull the Droid out of my pocket for 95% of my driving.


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## mizlplix (May 1, 2011)

Just a useless piece of information...

A standard fuel gauge reads current ohms. It is dependent on good, low/no loss wiring between the gauge and tank, as well as an accurate sender.

When you wire up a Zeva loop to measure your current flow, you are replacing the old wiring and tank sender. You are keeping the best part of the system, the gauge.

Even if your stock gas gauge didn't even work well, it is a good possibility the new SOC system will still be good.

Miz


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## ruckus (Apr 15, 2009)

mizlplix said:


> A standard fuel gauge reads current ohms. It is dependent on good, low/no loss wiring between the gauge and tank...


So I should use 4/0 wire on the gauge too?


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## mizlplix (May 1, 2011)

Best to use a superconductor, oh wait, they are not commercial yet. : )

Miz


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