View Full Version : what to look for when buying DC Ammeter
chitown1234
02-01-2009, 01:08 PM
also
what to avoid in specs
good sites to buy a meter from?
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Q-Hack!
02-01-2009, 01:41 PM
also
what to avoid in specs
good sites to buy a meter from?
In my mind, you aren't worried about accuracy to 5 nines. Go for price and don't worry about it.
H2OPWR
02-01-2009, 02:42 PM
I buy them from a company called Futurlec. Google it and you will find the site. Good accuracy and about $9.00 each.
Painless
02-01-2009, 02:51 PM
I buy them from a company called Futurlec. Google it and you will find the site. Good accuracy and about $9.00 each.
Larry,
In one of your videos you mention a cheap clamp on ammeter you have? How much and where for that one?
H2OPWR
02-01-2009, 03:03 PM
Larry,
In one of your videos you mention a cheap clamp on ammeter you have? How much and where for that one?
The cheap clamp meter that I have was $125.00. It does a nice job of measuring volts and Ohms. I will not even try it any longer with amps it is way off. My test results would look great but I would not only be deceiving everyone else I would be deceiving myself. Clamp meters that do a good job with all phases of high amp measuring are expensive. I have found that inexpensive panel meters with a shunt are very accurate but getting a good multi meter to be accurate and also measure the number of amps we use is practically impossible. The Fluke that I use is very very accurate but will set you back close to $400.00. If you or anyone wants accurate readings my best advice is to go with panel meters.
BoyntonStu
02-01-2009, 03:40 PM
The cheap clamp meter that I have was $125.00. It does a nice job of measuring volts and Ohms. I will not even try it any longer with amps it is way off. My test results would look great but I would not only be deceiving everyone else I would be deceiving myself. Clamp meters that do a good job with all phases of high amp measuring are expensive. I have found that inexpensive panel meters with a shunt are very accurate but getting a good multi meter to be accurate and also measure the number of amps we use is practically impossible. The Fluke that I use is very very accurate but will set you back close to $400.00. If you or anyone wants accurate readings my best advice is to go with panel meters.
"The cheap clamp meter that I have was $125.00. "
In my book, $125 ain't cheap.
Cheap is a $2.99 mulitimeter from Harbor Freight and a 14" length of #10 magic copper wire.
This combination is accurate to within 3%-5% at currents up to about 40 Amps or so. That is a very CHEAP and accurate way to measure DC Amps.
See my previous posts on the #10 magic wire.
BoyntonStu
H2OPWR
02-01-2009, 04:51 PM
"The cheap clamp meter that I have was $125.00. "
In my book, $125 ain't cheap.
Cheap is a $2.99 mulitimeter from Harbor Freight and a 14" length of #10 magic copper wire.
This combination is accurate to within 3%-5% at currents up to about 40 Amps or so. That is a very CHEAP and accurate way to measure DC Amps.
See my previous posts on the #10 magic wire.
BoyntonStu
I totally agree that $125.00 is not cheap but for a Clamp meter that will measure high amps it is as cheap as it they come cheap. Clamp meters are much more than multi meters that are not designed for high amps. That is why I recommended panel meters. They are cheap and accurate and can be mounted in a project box in the vehicle.
Larry
Painless
02-01-2009, 07:29 PM
"The cheap clamp meter that I have was $125.00. "
In my book, $125 ain't cheap.
Cheap is a $2.99 mulitimeter from Harbor Freight and a 14" length of #10 magic copper wire.
This combination is accurate to within 3%-5% at currents up to about 40 Amps or so. That is a very CHEAP and accurate way to measure DC Amps.
See my previous posts on the #10 magic wire.
BoyntonStu
Stu,
If you recall, I tried your shunt setup with my last test cell but found that the readings bumped up and down a lot over a wide range. When I double checked with my meters built in amp function that issue stopped.
Not sure what caused that.
chitown1234
02-02-2009, 05:04 PM
panel meters may be the best way to go is there a way to see what the amps out put is from the cars alt with it so i can put the right fuse in my set up
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H2OPWR
02-02-2009, 05:25 PM
panel meters may be the best way to go is there a way to see what the amps out put is from the cars alt with it so i can put the right fuse in my set up
I am not sure that I completely understand your question.
If you want to know the maximum output of the alternator then the only way you will be able to find out is to call the parts department of a dealership that sells your type of vehicle. Just keep in mind that the amperage rating they quote will be MAX amp draw. Most alternators will not sustain that output for more than a few minutes. Once they get hot your output will fall 10 to 20 percent.
If you want to find out the maximum available amperage you could use in your HHO Device that is quite a bit harder. First you need to find out your alternator capacity. Hot load not peak. Then you do need access to a good accurate amp meter of some kind. Then with everything on that you can turn on hopefully including a partially discharged battery and measure the output of the alternator and subtract that from Max hot load. Then do not use all of the available current left. You simply do not want to push the limit too close. You will find yourself stranded or worse. Play it safe when you calculate how much current you can use. Most vehicles can handle 15 amps stock many can handle much more.
Hope this helps but what you are trying to do is hard to do.
Larry
chitown1234
02-03-2009, 05:07 AM
ok thanks larry for you help
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BoyntonStu
02-03-2009, 03:36 PM
Stu,
If you recall, I tried your shunt setup with my last test cell but found that the readings bumped up and down a lot over a wide range. When I double checked with my meters built in amp function that issue stopped.
Not sure what caused that.
Russ,
Sorry that happened to you.
Watch my videos, the Amps do not vary more than 0.1A in any of them.
I have checked the accuracy several times.
There is no technical reason (other than w minimum temperature effect), why a #10 copper wire shunt would not equal any other shunt's performance.
Strange things are always possible.
BoyntonStu
H2OPWR
02-03-2009, 03:43 PM
Russ,
Sorry that happened to you.
Watch my videos, the Amps do not vary more than 0.1A in any of them.
I have checked the accuracy several times.
There is no technical reason (other than w minimum temperature effect), why a #10 copper wire shunt would not equal any other shunt's performance.
Strange things are always possible.
BoyntonStu
Stu, I think the amp bouncing Russ was seeing is because his cell was doing exactly what mine is right now. With the large plate stack and the large volume of gas it is hard to keep the electrolite level steady. As the electrolite level constantly raises and lowers so will the amp draw. I am not certain just guessing.
Larry
Painless
02-03-2009, 06:43 PM
Stu, I think the amp bouncing Russ was seeing is because his cell was doing exactly what mine is right now. With the large plate stack and the large volume of gas it is hard to keep the electrolite level steady. As the electrolite level constantly raises and lowers so will the amp draw. I am not certain just guessing.
Larry
Larry,
That was with the small test cell, who knows, perhaps the copper wire was damaged in some way.
Russ.
Does anyone know where I can get an amp meter to mount on my vehicle that goes higher than 60 amps and won't break my wallet too much.The 60 amp one I use now was about $38 at Napa.
Painless
02-04-2009, 08:36 AM
Does anyone know where I can get an amp meter to mount on my vehicle that goes higher than 60 amps and won't break my wallet too much.The 60 amp one I use now was about $38 at Napa.
How about using one of these mv LCD meters with a shunt?
http://www.futurlec.com/Panel_Meters.shtml
Russ.
How about using one of these mv LCD meters with a shunt?
http://www.futurlec.com/Panel_Meters.shtml
Russ.
Russ I looked at the site and I don't quite follow what you mean.Bear in mind the electricians hat I own is size small if you know what I mean.
gashead
02-04-2009, 09:22 AM
i purchaced a 30 amp meter from ( the scooter store ) and it will read 20-21 amps before my cell blows a 15 amp fuse, i have a 50 amp from harbor freight tools, but its hard to read ( 25 amp increments ). im still looking
Gary Diamond
02-04-2009, 12:03 PM
i purchaced a 30 amp meter from ( the scooter store ) and it will read 20-21 amps before my cell blows a 15 amp fuse, i have a 50 amp from harbor freight tools, but its hard to read ( 25 amp increments ). im still looking
What kind of fuse are you using? Is it a slow blow type? Is your wire large enough? Sure you can have a crapy meter, why not test it, use a known load with a known source, IF YOU USE a battery charger is not a known source!
A battery charger has a very high AC 60 ripple on it, God only knows what that will do for your reading. When you use a battery with a charger the battery becomes a big Cap. which will clean up the AC ripple.
SO A BATTERY CHARGER ALONE, IS A WORTHLESS THING, WHY NOT BUILT THE POWER SUPPLY FROM FREE COMPUTERS AS STU POINTED OUT.
gashead
02-04-2009, 12:22 PM
What kind of fuse are you using? Is it a slow blow type? Is your wire large enough? Sure you can have a crapy meter, why not test it, use a known load with a known source, IF YOU USE a battery charger is not a known source!
A battery charger has a very high AC 60 ripple on it, God only knows what that will do for your reading. When you use a battery with a charger the battery becomes a big Cap. which will clean up the AC ripple.
SO A BATTERY CHARGER ALONE, IS A WORTHLESS THING, WHY NOT BUILT THE POWER SUPPLY FROM FREE COMPUTERS AS STU POINTED OUT.
i am using an inline 10 gauge wire fuse holder with a 15 amp automotive fuse not the maxi fuse. i think the meter is junk, it is consistant though. consistantly 5 - 6 amps too high lol
Painless
02-04-2009, 04:24 PM
Russ I looked at the site and I don't quite follow what you mean.Bear in mind the electricians hat I own is size small if you know what I mean.
hg2,
You could copy Stu's design. Take 12" of 10 gauge wire and attach the millivolt meter across it in parallel. The number of millivolts will equal the number of amps as the resistance of 12" of 10 gauge is 1 ohm.
Russ.
BoyntonStu
02-04-2009, 05:04 PM
hg2,
You could copy Stu's design. Take 12" of 10 gauge wire and attach the millivolt meter across it in parallel. The number of millivolts will equal the number of amps as the resistance of 12" of 10 gauge is 1 ohm.
Russ.
Do NOT connect the voltmeter leads at the ends of the wire where it is attached to other wires.
Do it like this X____:_____<12">________:_____X
X is were the wire connects to the battery and the cell.
Attach the voltmeter leas to ":" spaced 12" apart.
BoyntonStu
Stu is the 10 gauge wire in line with the voltage going to my cell or is it isolated somehow?The reason I ask is because I have to use 6 gauge wire to power the cell with the high amp draw I have now.
Sorry if I'm not clear on this,electric is just not my strong suit.
BoyntonStu
02-04-2009, 07:42 PM
Stu is the 10 gauge wire in line with the voltage going to my cell or is it isolated somehow?The reason I ask is because I have to use 6 gauge wire to power the cell with the high amp draw I have now.
Sorry if I'm not clear on this,electric is just not my strong suit.
For #6 copper wire, use 4.75" between your voltage measurement points.
4.75" of #6 is equivalent to 12" of #10.
BoyntonStu
BoyntonStu
02-04-2009, 09:43 PM
Sorry Stu but your math is wrong. To get .001 ohm resistance you need 30.372in of #6
My bad!
I was thinking the inverse ratio.
I calculate 29.85"
30" will do it!
Thanks,
BoyntonStu
Thanks for the help guys I got it now.I'm glad I got some awg 6 left over from rewiring that's stuff's not cheap.
Q-Hack!
02-05-2009, 02:25 AM
Just make sure you don't coil it up... It needs to be relatively straight. Finding a place for 30 inches of wire under the hood could be problematic.
Edit: You know, I say that, but if we are measuring DC does that really apply? Inductors tend to block AC and pass DC. One of you EE's want to confirm or deny my previous statement?
Will it hurt just to make a turn or two,you're right I'd rather not have 30" of wire laying on top of everything.
Painless
02-05-2009, 08:41 AM
Will it hurt just to make a turn or two,you're right I'd rather not have 30" of wire laying on top of everything.
You could always affix it to the underside of your hood?
Q-Hack!
02-05-2009, 12:38 PM
I know for a fact that a single 30' circle would be good. It's when you start looping the wire back over itself that you will have trouble.
Both are good ideas to consider thanks again.
BoyntonStu
02-05-2009, 04:36 PM
30" of #6 wire allows you to directly measure Amps in mili-Volts.
14 mV = 14 A
Very convenient.
However using only 15" will double the reading and it may still be useful and accurate.
14 mV with 15" of #6 = 28 A.
Since you will be using a digital meter, you should not have any problem seeing the tenths digit.
7.0 mV = 14 Amps
BoyntonStu
Stu when you say the tenths digits will that be amps down to the tenths or mv or both?
BoyntonStu
02-05-2009, 07:59 PM
Stu when you say the tenths digits will that be amps down to the tenths or mv or both?
Let's imagine that your meter reads 7.4 mV.
That would indicate 14.8 Amps.
BoyntonStu
That clears it up I understand now,thanks Stu