Ammeter

[bluecamel]

I've been having all kinds of fun with diagnosing and fixing my charging system. Most of the basic tests require a DC ammeter that can read up to 10 - 15 amps (I think). Every multimeter I can find in town, besides the fancy pants $150+ meters, only go up to something around 150mA for measuring DC current. Plenty go higher for AC, but not DC. And no one has a dedicated ammeter.

Can anyone recommend a store that's likely to be local where I can find a decent, fairly inexpensive (under $30 would be nice) ammeter? I've tried Autozone, O'Reilly's, Advance Auto Parts, Radio Shack, Home Depot, and the local car stereo shops. Maybe there's one of these in some unlikely place, like a Walgreens or Dillons?

Thanks!

Branton

[Sev]

To get something that can measure a lot of current you need to spend a lot of money. Or... you can build a shunt. I think I've still got the instructions at home. Basically it's a peice of wire with a calibrated resistance that you measure the voltage drop across and it'll tell you the current.

What test are you trying to do that you need to measure 15amps of current? The only thing that should draw that much (that I can think of off the top of my head) is the starter circuit.

I'll write out the charging system checks for you tonight after work. You shouldn't really need an ammeter in any event.

[bluecamel]

I'm trying to go through this:

http://home.earthlink.net/~trinomial/DOHCcharge.html

Some of the same things are talked about in my Clymer manual, where I need to put an ammeter with an inline fuse in place of the main 30A fusible link. This, I guess, is supposed to tell me whether the system is charging or not (somehow, I take it, this is more accurate than testing voltage across the battery).

I really want to do this because the guy at the local battery shop that sold me the new battery also put a clip around ammeter around several spots on my system and was getting strange amperage readings. For example, around the line coming from the stator, amperage rose with rpms. The same with the line coming out of the rectifier/regulator. However, amperage on the positive cable to the battery actually dropped while revving the engine. It would start at 8 and drop. So, I just want to test everything and make sure there's not some strange short or draw somewhere in the system...or at the very least, verify that he didn't do something wrong, like check AC instead of DC.

I would really appreciate any instructions on building the shunt or testing the system! Thanks!

[slimcolo]

Try using a ammeter like the ones that come with a oil pressure gage. The ones that mount under dash.

[Sev]

Sorry, I forgot about this thread.
You need one of these


Okay, get the bike running then set your multimeter to...
20 volts DC, measure the voltage across the battery at idle. It should be just below or just above 12.8 volts.

Rev it up to 5000rpm and take the same reading. It should be closer to 14 or 15 volts.

If it isn't there is a problem with your charging system. Lets try to find it.

set the multimeter to something in the range of 200 volts AC

Find the three yellow wires coming out of your alternator.

Follow them back to the connector. Disconnect the connector and measure the AC voltage between the wires at 5000rpm. You'll need a friend to rev it up for you. Think of the three wires as A,B,C

Do:
AB
BC
CA

Each should be in the range of 60-80 volts if memory serves. But your manual will have better stats. If one is substantially lower you may have a bad coil.

Turn the bike off and switch your multimeter too the ohmmeter. The higher the reading the better. Now stick the positive lead into one of the yellow wires and touch the negative to the frame. There should be infinite resistance or no continuity. Test the other two wires in a similar matter. If you get continuity then you've got a bad coil and need a new stator.

If the alternator output is good, then you need to check your connections to the regulator/rectifier. If the connections are good going TO the reg/rect and if they're good from the reg/rect to the battery, then you need to replace the reg/rect.

It's fairly simple once you get things broken down into little portions/sections.

[bluecamel]

Thanks a ton, Sev! I've actually done everything you said, but I'm going to be very specific below. Something out of the ordinary is going on in mine, obviously.

Sorry, I forgot about this thread.
You need one of these


Okay, get the bike running then set your multimeter to...
20 volts DC, measure the voltage across the battery at idle. It should be just below or just above 12.8 volts.

Rev it up to 5000rpm and take the same reading. It should be closer to 14 or 15 volts.

Well, this is the fun one. When I installed the new stator, it first was in that range. Then the next day, it wasn't. Same thing after I installed the regulator/rectifier. At first, it was in the correct range, but the next day, it was down around 12 V.

If it isn't there is a problem with your charging system.

Indeed

Lets try to find it.

set the multimeter to something in the range of 200 volts AC

Find the three yellow wires coming out of your alternator.

Follow them back to the connector. Disconnect the connector and measure the AC voltage between the wires at 5000rpm. You'll need a friend to rev it up for you. Think of the three wires as A,B,C

Do:
AB
BC
CA

Each should be in the range of 60-80 volts if memory serves. But your manual will have better stats. If one is substantially lower you may have a bad coil.

Before I got the new stator, I was getting around 12 V on all but one. The other was getting 3 V or so. After the new stator, I still only got 10-15 V on each. This is when I was told that it must be the rectifier, and the rectifier actually did test bad on the diodes.

Turn the bike off and switch your multimeter too the ohmmeter. The higher the reading the better. Now stick the positive lead into one of the yellow wires and touch the negative to the frame. There should be infinite resistance or no continuity. Test the other two wires in a similar matter. If you get continuity then you've got a bad coil and need a new stator.

All checked out okay here.

If the alternator output is good, then you need to check your connections to the regulator/rectifier. If the connections are good going TO the reg/rect and if they're good from the reg/rect to the battery, then you need to replace the reg/rect.

It's fairly simple once you get things broken down into little portions/sections.

Well, it sure doesn't seem simple. I've also tested the rotor myself as well as had it tested by two shops. We all say it's fine. My only conclusion is that something is intermittently shorting. Does that sound reasonable?

The shop apparently hasn't even looked at my bike in the week and a half they've had it. I was tempted to steal it back and just check every single damn wire, but decided to wait and see what they say.

[Sev]

[quote="bluecamel]Before I got the new stator, I was getting around 12 V on all but one. The other was getting 3 V or so. After the new stator, I still only got 10-15 V on each. This is when I was told that it must be the rectifier, and the rectifier actually did test bad on the diodes. [/quote]


You should be getting in the range of 50-70v AC across those three plugs. Not 12volts.

If you're only getting 12volts then either your magnets are dieing or your stator is gone. The rectifier won't affect the AC output off the alternator all it does is turn AC to DC with a series of diodes.

[bluecamel]

Did I mention that even though I was only getting that voltage, I was getting a voltage across the battery of 13-14.5? Does that make sense? And it was a new stator that otherwise tests well.

This is why I've left it with the guys at the shop. I just hope they get to it before another week.

[crazypj]

you can make a shunt with 8 gauge wire 19.1" between measuring points (measure voltage drop in Millivolts.) otherwise visit your favorite auto shop and buy a cheap amp meter
PJ