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DMM Max Function vs Peak Voltage

havinnoj

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Oct 17, 2012
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What's the difference between the "Max" function on the DMM and using a Peak Voltage Adapter from CDI or Fluke to check "peak voltage"?

I need to test an ignition system on an ATV and can't tell what the true difference is. Any help is appreciated :thumbup:
 
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zkling

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Jan 23, 2007
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Most DMM's don't have a high enough frequency range and response to capture the true peak output of a stator. The DVA or peak adapter uses a cap based circuit that holds a charge for a little while longer while slowly bleeding off and allows time for even the cheapest meter to truly read the max output voltage (peak). You can make one pretty easily but sometimes the parts are hard to come by locally.
 
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havinnoj

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Joined
Oct 17, 2012
Messages
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Most DMM's don't have a high enough frequency range and response to capture the true peak output of a stator. The DVA or peak adapter uses a cap based circuit that holds a charge for a little while longer while slowly bleeding off and allows time for even the cheapest meter to truly read the max output voltage (peak). You can make one pretty easily but sometimes the parts are hard to come by locally.

The ignition and alternator coils need to be above 100V and the ignition pulse generator above 0.7V. I'll be using an Extech EX330 which cites a maximum input voltage of 600 VDC. Frequency range is 0.001Hz to 10MHz. Would the DMM still not work?
 

zkling

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Couple things. A stator puts out an ac voltage. It is essentially a small generator. It's frequency and voltage depends on model, poles, and cranking RPM. I mostly use mine for work on older outboard motors where voltage is <400v. It is a standard tool when working on outboards. The frequency spec you are looking at is the frequency the meter can measure you need to look at the ac voltage at which which frequency range the meter can measure, it's called bandwidth. Without looking up that meter it is probably in the 50-75Hz range, as most basic meters are designed. I think I actually have that meter but in craftsman clothes. That meter will not work by itself. For a few reasons. If you want to discuss it further in depth we can. It will give you a goofy averaged value probably somewhere in the 50-70v range.

You will either need a higher end meter with a larger ac frequency range (labeled bandwidth in meter specs), a DVA peak detector or an oscilloscope. If you are sure the max voltage you are going to get out of your stator is only ~100v that is pretty low and you should be able to find parts pretty easily. The ingnition pulse generator is commonly called the trigger and is what starts the whole process. Do a search for homebuilt DVA, it will probably take you to a boating forum with a simple schematic and instructions.

Do you have the service manual for the quad you are working on?
 
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havinnoj

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Joined
Oct 17, 2012
Messages
59
Couple things. A stator puts out an ac voltage. It is essentially a small generator. It's frequency and voltage depends on model, poles, and cranking RPM. I mostly use mine for work on older outboard motors where voltage is <400v. It is a standard tool when working on outboards. The frequency spec you are looking at is the frequency the meter can measure you need to look at the ac voltage at which which frequency range the meter can measure, it's called bandwidth. Without looking up that meter it is probably in the 50-75Hz range, as most basic meters are designed. I think I actually have that meter but in craftsman clothes. That meter will not work by itself. For a few reasons. If you want to discuss it further in depth we can. It will give you a goofy averaged value probably somewhere in the 50-70v range.

You will either need a higher end meter with a larger ac frequency range (labeled bandwidth in meter specs), a DVA peak detector or an oscilloscope. If you are sure the max voltage you are going to get out of your stator is only ~100v that is pretty low and you should be able to find parts pretty easily. The ingnition pulse generator is commonly called the trigger and is what starts the whole process. Do a search for homebuilt DVA, it will probably take you to a boating forum with a simple schematic and instructions.

Do you have the service manual for the quad you are working on?

Thanks for all this info.. though I'm afraid I won't digest it fully! The 100v is the minimum peak voltage spec for a couple of things. So I could very well see it being higher but probably not magnitudes higher. Here's a link to the pdf file to test the ignition: 2000-2001 CR250 Ignition.

Interesting thought on building one from scratch. I'll take a look at that. :beer:
 
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zkling

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If you do a google search for that honda part number. 07HGJ-
0020100 it looks like many a people have successfully built one. The voltage sounds quite a bit lower than most outboards. Otherwise CDI and a few other folks make a DVA for ~$50
 
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havinnoj

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Oct 17, 2012
Messages
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If you do a google search for that honda part number. 07HGJ-
0020100 it looks like many a people have successfully built one. The voltage sounds quite a bit lower than most outboards. Otherwise CDI and a few other folks make a DVA for ~$50

Thanks. I'll looking to making or buying one. A last question.. is there a standard width between connections on multimeters (i.e. will the 2 prongs on the CDI DVA plug into most multimeters)?
 

zkling

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Thanks. I'll looking to making or buying one. A last question.. is there a standard width between connections on multimeters (i.e. will the 2 prongs on the CDI DVA plug into most multimeters)?

Yes most dual banana jacks are a standard 3/4" width CTC IIRC.
 
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