# cheap shunt



## dray (Aug 1, 2008)

for an inexpensive shunt when using 2/0 wire for bat. connections i put a metal screw into the 2/0 wire next to the 1st batt. neg. terminal and another 19.5 inches away on the same wire. two wires than ran into the vehicle cab to my meter. the wire closest to the neg. bat. terminal is the neg. lead to the meter. this is very close to the resistance value of a 50 mv 400 amp shunt. with a 50 mv meter movement it read very close to the same current as a 50 mv 400 amp shunt which i finally installed.


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## DIYguy (Sep 18, 2008)

dray said:


> for an inexpensive shunt when using 2/0 wire for bat. connections i put a metal screw into the 2/0 wire next to the 1st batt. neg. terminal and another 19.5 inches away on the same wire. two wires than ran into the vehicle cab to my meter. the wire closest to the neg. bat. terminal is the neg. lead to the meter. this is very close to the resistance value of a 50 mv 400 amp shunt. with a 50 mv meter movement it read very close to the same current as a 50 mv 400 amp shunt which i finally installed.


I got my meter and shunt for free out of an old DC weld power supply. Perfect.

see pics....


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## chamilun (Jun 17, 2008)

were there calculations you used to determine the 19.5 inches? 

very ingenious idea


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## dray (Aug 1, 2008)

chamilun said:


> were there calculations you used to determine the 19.5 inches?
> 
> very ingenious idea


yes there was. "Thelenchannel.com/1wire.php" has a resistance chart for copper wire up to and including 4/0 wire. the resistance of a 50mv 400 amp shunt is equal to .05 divided by 400 which eqauls .000125 ohms.
2/0 wire has .077 ohms per 1000 ft. or .000077 ohms per foot.
.000125 divided by .000077 equals 1.623 feet of wire. which is really close to 19 and 5/8 inches. rapped wire around metal wood screws taped over connections and ran wires to the meter.


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## ElectriCar (Jun 15, 2008)

Here's a chart of resistance/1000' for various wire. In the chart, 00= 2/0


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## Guest (Dec 5, 2008)

Nice snag on that shunt and meter. Nice meter and I think I my go hunt for one or two myself. That would be perfect for my Ghia. Never thought of using one from an old DC welder. I am going to ask my neighbor. He has loads of ac arc welders. But a DC welder! Where might one find one of those. 

Pete : )






DIYguy said:


> I got my meter and shunt for free out of an old DC weld power supply. Perfect.
> 
> see pics....


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## Qmavam (Aug 17, 2008)

dray said:


> for an inexpensive shunt when using 2/0 wire for bat. connections i put a metal screw into the 2/0 wire next to the 1st batt. neg. terminal and another 19.5 inches away on the same wire. two wires than ran into the vehicle cab to my meter. the wire closest to the neg. bat. terminal is the neg. lead to the meter. this is very close to the resistance value of a 50 mv 400 amp shunt. with a 50 mv meter movement it read very close to the same current as a 50 mv 400 amp shunt which i finally installed.


 This method works fine, just be aware that copper has a temperature coefficient of 0.2183% per degree Fahrenheit.
So the shunt will change resistance by 13% from 30*F to 90*F. 
If it is calibrated at 70 degrees then the meter would have an error of 4.6% at 90 degrees and 50 degrees.
Proper shunts are designed with low temperature coefficients.
Mike


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## DIYguy (Sep 18, 2008)

gottdi said:


> Nice snag on that shunt and meter. Nice meter and I think I my go hunt for one or two myself. That would be perfect for my Ghia. Never thought of using one from an old DC welder. I am going to ask my neighbor. He has loads of ac arc welders. But a DC welder! Where might one find one of those.
> 
> Pete : )


There are many types of weld power supplies. Typically, GMAW (commonly called MIG) power sources are DC output. The newer ones, that have meters, are often digital... the older ones tend to be analogue. There are AC/DC and DC SMAW (Stick) welders around also that may work... but the range may not be as high, depending what you find. Older industrial "MIG" welders might be your best choice. Here is a pic of the shunt.

Unfortunately, the voltage range on the output of these machines is much lower than needed for an EV, so the voltmeter from the welder wont be usable.

Regards,
Gary


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## Qmavam (Aug 17, 2008)

DIYguy said:


> Unfortunately, the voltage range on the output of these machines is much lower than needed for an EV, so the voltmeter from the welder wont be usable.
> 
> Regards,
> Gary


 I went on a search for shunts, I know I bought one for $9.95. I found them but they are lower amperage than you need (200amp). I needed one for my gokart. I did find a link to higher amperage but no prices that I could find quickly.
http://www.deltecco.com/catalog.html
Regarding the voltage range of the voltmeter: most meters that you buy (at least surplus) need to have a series resistor added to make them read
what the scale says. It's not hard to figure out the value of the resistor needed to make the meter match the scale. Ask and I'll find a page or write the description.
There is software available (maybe free) that produces artwork on the meter face so you can make the meter anything you want. Such as 0 to 10,000 RPM, full/empty, speed 0 to 80 MPH, even 0 to 1 milliamp, 0 to 1000 amps, 0 to 12v volts or 0 to 180 volts. And then with a series resistor
or a shunt or both you can make the scale and the measurement match.
BTW I saw these meters for $7.95, they look like pretty good meters for that price.
http://www.hosfelt.com/ Hmm, looks like you'll need go there, click find, type meters, then click panel to get the page.
Let me know if anybody needs help adjusting a meter.
Mike


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## DIYguy (Sep 18, 2008)

Qmavam said:


> I went on a search for shunts, I know I bought one for $9.95. I found them but they are lower amperage than you need (200amp). I needed one for my gokart. I did find a link to higher amperage but no prices that I could find quickly.
> http://www.deltecco.com/catalog.html
> Regarding the voltage range of the voltmeter: most meters that you buy (at least surplus) need to have a series resistor added to make them read
> what the scale says. It's not hard to figure out the value of the resistor needed to make the meter match the scale. Ask and I'll find a page or write the description.
> ...


Very kewl... regarding the volt meter. That sound right... I just might take u up on that.  I like to find ways to make things work without spending big $. Maybe I am just cheap! 

G


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## Qmavam (Aug 17, 2008)

DIYguy said:


> Very kewl... regarding the volt meter. That sound right... I just might take u up on that.  I like to find ways to make things work without spending big $. Maybe I am just cheap!
> 
> G


Well, we could say we're just frugle, money is a tool and we use it wisely.

I got some good deals while putting together my electric gokart, picture attached.
I bought the gokart for $100, I was given the DC motor, found an Alltrax controller on Craigslist for $100+$10 shipping. $9.00 volt and amp meters.
The shunt I bought was $9.95. I picked up 3 batteries from a wrecker service junkyard for $5.00 each. They have served me well for about a month, but I'm about to splurge, next week I'm going to get 4 #27 deep cycle batteries from Sam's. I have a battery charger on order from Kipoint
in Taiwan should also be here next week. I have some mods to make going from 36 to 48 volts.
Hey, I ran across an interesting voltmeter modification a while back,
I hope to use it on gokart. I'm only interested in voltages from 42v to 60 volts on my gokart, 0 to 40 is wasted on the scale. So this circuit causes the meter to read 0 at 40 volts and fullscale at 60 volts, and half scale at 50 volts. It expands the scale making it easier to see small differences.
I hope I explained that well. To say it another way, instead of the meter reading 0 to 60 volts it reads 40 volts to 60 volts. Oh, and it only uses two parts. http://www.edn.com/archives/1994/012094/02di2.htm
I did run into one problem that I think is easily fixed. The parts have a maximum voltage of 35v, but if I put a 2 to 1 voltage divider on the 48 volt battery, I can monitor the 16 volts from the voltage divider and display it as 48 volts. All this might seem complicated but it is easy to do. Hope I haven't bored you. If I can help, let me know.
Check out the gokart.
Mike


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