# Digital tachometer? DC clamp meter?



## Woodsmith (Jun 5, 2008)

Now I have a small 6 1/2" golf buggy motor to experiment with I want to know how fast it spins so I can work out gear ratios and the like for a small learning curve project.

I have been looking at this sort of hand held contactless tacho on Ebay.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=170417291504&ssPageName=STRK:MEWAX:IT
I was just wondering if there are any recommendations over this sort of kit, what to look for and what to avoid. I know it is cheap anyway but no point spending even a little money on rubbish.


Also, I was thinking of getting a DC clamp meter to measure working currents to a motor. Something like this one.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=350241570050&ssPageName=STRK:MEWAX:IT
Again, any suggestions before I spend my hard earned money?

Thanks.


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## Amberwolf (May 29, 2009)

I have used that exact tach (borrowed from a wheechair repair place) to measure some of my powerchair motors and other things. It will hold the peak speed, and show you the current speed, toggling between them pressing that button. 

Just stick on some of the reflective sticker material included with it on the shaft of whatever you are measuring and it works fine. It's ok with just like a white dot on a dark background, too, but much better with the sticker stuff.

I dont' know it's accuracy compared to any other one, but it was accurate for the items I already knew the RPM of.
________
Christabell


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## Tesseract (Sep 27, 2008)

I also have the same tachometer and can also attest that it is accurate.

I long since lost the reflective stickers it came with, so now if I want to be really sure to get an accurate reading I spray paint the target flat black and then tape a piece of aluminum foil onto one spot. 

As for the clamp meter, it looks just like a B&K Precision 369B, but in different colors and can read higher currents... I have said B&K meter and let's just say that for professional use it leaves much to be desired. It's not terribly accurate with "high crest factor" currents (i.e. - reading the battery current) and it's not too rugged, either (the jacks are all wobbly even though I hardly use them), but it's not a *bad* meter, it just perfectly exemplifies why paying twice as much for the Fluke was worth the price paid, is all. I still use it when I need to make two measurements at the same time, I just put it on the side I know will see the more continuous current reading.


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## Woodsmith (Jun 5, 2008)

That's good, thank you both.

I will get the tacho and keep looking for the clamp meter. 
I will need to think about how much I spend on the clamp meter as I won't be using it in any professional capacity. I already have good ones for my electrical work but they are ac only.


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## major (Apr 4, 2008)

Woodsmith said:


> I will get the tacho and keep looking for the clamp meter.
> I will need to think about how much I spend on the clamp meter as I won't be using it in any professional capacity. I already have good ones for my electrical work but they are ac only.


Hey woods,

Check out this one. http://www.diyelectriccar.com/forum...r-100-amps-36368p4.html?highlight=clamp+meter 

Post #35 shows a picture. Post #30 gives the link.

major


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## Woodsmith (Jun 5, 2008)

Cheers for that major, I will look out for one this side of the pond and compare shipping costs.

As an aside, one of my relatives sent me a $20 bill last Christmas. It sits on the shelf as I'm not sure what to do with it as it is hardly worth exchanging but it is not enough to spend on anything!


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## Woodsmith (Jun 5, 2008)

Jane347 said:


> Come here,all...
> [Dodgy link removed]
> Fantastic place,go there and have a try,
> Big surprises are waiting for you.


I ain't clicking on that link!
Who knows where the spammers may take me!


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## Woodsmith (Jun 5, 2008)

I have a new toy!

I clicked the 'Buy it now' button on the 21st and this morning, the 23rd, a package is delivered. Excellent service.

I have been playing with the tachometer to see what it is like. 
First impressions are that it feels a little 'plasticy' but that is normal for cheap stuff nowadays. It cost £17.99 and that included P+P and a plastic foam lined case, some reflective strips and some silica gel.
It takes four AA batteries. The first battery is a little difficult to fit as the terminals are a little too tight but the rest are ok.
It reads instantaneous RPM and it also counts revolutions.

I tried it on my lathe first and took this video.


I then tried it on my golf buggy motor. I couldn't take video of that as I needed a hand and a foot to hold the leads on the car battery and a hand to hold the tacho. I decided not to put my mobile phone in my mouth!
At 12v the golf buggy motor spins at 1750rpm. I wonder if it will be a linear relationship with 3500rpm at 24v, 5250rpm at 36v and 7000rpm at 48v? If so I will need to rethink my tractor project or it will be a 40mph tractor!


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## Amberwolf (May 29, 2009)

Well, all the powerchair motors I tested here with that tach at voltages from 12V to 48V in increments of 12V ended up linearly increasing the unloaded RPM with voltage. They're PMDC brushed motors, both 2pole and 4pole, so similar in construction to golf buggy motors (especially if the GB motor you have is also PMDC).
________
PRETTYBABE


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