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Discussion Starter #1 (Edited)
I wanted a voltmeter and ammeter on my scoot. While a voltmeter is frequently adequate, without an ammeter you can't tell if the battery is being charged, being discharged, or is fully charged. I assembled a digital voltmeter/ammeter and outline its construction here. If you are comfortable with soldering, reading schematics and like this sort of thing, I intend this as an example of what is possible. If not, best to step away...

The finished product is seen in f1.jpg. My 2018 b650 is on, but not yet started. The battery reads 11.95 V and 9.9 A is flowing out of the battery (minus sign), i.e., discharging it. After starting and at idle, f2.jpg indicates the battery now reads 14.20 V and 4.6 A is flowing into the battery, i.e., charging it.

The "voltmeter ammeter.jpg" image shows the schematic for the project.

ABOVE the horizontal dashed line, the components to display the readings are shown. They are all mounted together in a small enclosure. There are two LCD panel meters, a voltage regulator and two resistors. All part numbers are shown. The upper panel meter reads full scale (2000) with 20 V applied. This will be used to read battery voltage; the schematic wires up the middle decimal point so the display becomes 20.00 as required. The lower panel meter reads full scale (2000) with 0.2 V applied. This will be used to read battery current by sensing the voltage across a 0.001 ohm resistor in series with the battery. Since current = voltage/resistance, full scale current is 0.2 V / 0.001 Ohm = 200 A; the schematic wires up the third decimal point so the display becomes 200.0 as required. The back of the small enclosure is shown in f3.jpg all wired up and ready to go. Files f4.jpg and f5.jpg show the meters under test: f4 reads 12.72 V and 0 A (correctly!); f5 demonstrates the backlighting in a dark room.

BELOW the horizontal dashed line, the current sensing resistor in series with the battery is shown in schematic. Note: the red components (two circulator voltmeters) are just the equivalent circuit of the panel meter circuit! The only thing to build from the bottom schematic is shown in f6.jpg: the 0.001 Ohm resistor is curled in appearance and soldered to two lugs. This assembly rides on a phenolic board for mechanical strength (f7.jpg). One end bolts to the ground terminal of the battery; the other end receives what was previously at the battery's ground terminal.

The wires marked A,B,C,D connect the battery area to wherever the meters are mounted. I mounted my meters to the rear of the front brake fluid reservoir using a bent aluminium bracket attached with clear silicone caulk, as seen in f8.jpg.

Is it accurate? I think so. With the bike on but not running, if I toggle between lo and hi beam headlights, the current increases by 0.8 A. This seems correct: lo beams are 2 x 55 W and hi are 2 x 60 W. 120 W - 110 W = 10 W increase, which at 12 V requires 10 W/12 V = 0.833 A. Riding today with a heated jacket liner (77 W), and the heat-troller set at about 50% duty cycle, The current would jump up and down by 77/12 ~ 6 A or so at idle. Ok.

Finally, I pulled the fuel pump fuse and cranked the scoot. It didn't start (of course) but indicated current around 60 A was being pulled by the starter. I can't find anything in the service manual to back up this finding. And note this represents a 0.06 V drop in the starter circuit across the current sensing resistor, so not enough to worry about.

damocles
 

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I disagree with your comment above:
"While a voltmeter is frequently adequate, without an ammeter you can't tell if the battery is being charged, being discharged, or is fully charged."


I have a 2017 650 Executive. I use continuously a plug into accessory outlet voltmeter. It shows the generator charging while the engine is running. It also shows the battery charge in volts when off. If it was being discharged while on a ride the volts would drop below 12 or so. when shut down and before starting I occasionally put an external voltmeter on on the Battery Tender pigtails and usually see 13 volts or so after being on the charger. Yes, this won't show the amps in it but does show the volts.
 

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I like both Volt and Amp's but learned many years ago an Amp meter can catch fire and burn up a car. Chrysler used Amp meters thru the 80's. 100% of all current from the Alternator went thru the Amp meter and they got very warm or meltdown hot.



Most newer Amp meters are really a Milliamp meter. It has a shunt and a bypass wire so when the calibrated armature sees current going one way or the other thru the shunt. But 80% of the total current goes thru the bypass wire.
 

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Discussion Starter #4
I can't really argue with this. From a voltmeter, you can know if you are charging (voltage reads high from alternator), or if you are using way too much power than the alternator can supply (voltage reads low because battery is discharging to help out). But you can't really tell if the battery is fully charged at any given moment. With an ammeter, you can see the current drop to zero. This means the battery is neither supplying current (because the alternator is handling everything) and also the battery is not storing any more electrons because it is fully charged (because enough time has elapsed to fully charge the battery). When running heated jacket/gloves, I want to know: if I shut the bike off right now, do I have a good chance there is enough battery power to start it again?

damocles

P.S. Really...I am just trying to get my post count to >=10, so I can see photos others have posted (and not just mine) to the forum :smile

I disagree with your comment above:
"While a voltmeter is frequently adequate, without an ammeter you can't tell if the battery is being charged, being discharged, or is fully charged."


I have a 2017 650 Executive. I use continuously a plug into accessory outlet voltmeter. It shows the generator charging while the engine is running. It also shows the battery charge in volts when off. If it was being discharged while on a ride the volts would drop below 12 or so. when shut down and before starting I occasionally put an external voltmeter on on the Battery Tender pigtails and usually see 13 volts or so after being on the charger. Yes, this won't show the amps in it but does show the volts.
 

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Discussion Starter #5
Great point. I put the current sensing resistor at the ground end of the battery for "safety". And also, with a maximum current of 60 A through a 0.001 Ohm resistor, that represents 3.6 W, which formally exceeds the 3 W rating of the resistor I used. Yikes! But that is the starting transient. Typical currents are far less than this: 15 A corresponds to 0.225 W. So I am hoping a fire is not in my future.

damocles

I like both Volt and Amp's but learned many years ago an Amp meter can catch fire and burn up a car. Chrysler used Amp meters thru the 80's. 100% of all current from the Alternator went thru the Amp meter and they got very warm or meltdown hot.



Most newer Amp meters are really a Milliamp meter. It has a shunt and a bypass wire so when the calibrated armature sees current going one way or the other thru the shunt. But 80% of the total current goes thru the bypass wire.
 

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Out of curiosity how did you calculate the exact size and shape of the piece of metal for the .001 ohm resistor? Not trying to be critical, and kind of hard to tell from the picture but the solder looks like it didn't flow out very well, like maybe not enough heat was used. I would be somewhat worried about one of those solder joints cracking, either through stress or vibration, or from heating, which would probably leave you instantly stranded. (Just trying to help you get your post count up. ;) )
 

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Discussion Starter #7
Out of curiosity how did you calculate the exact size and shape of the piece of metal for the .001 ohm resistor? Not trying to be critical, and kind of hard to tell from the picture but the solder looks like it didn't flow out very well, like maybe not enough heat was used. I would be somewhat worried about one of those solder joints cracking, either through stress or vibration, or from heating, which would probably leave you instantly stranded. (Just trying to help you get your post count up. ;) )
This current-sensing resistor was purchased, not made by me. This project was put together 13 years ago, and used for 5 years on a previous bike. I believe the resistor was made by Vishay/Dale, but the present offerings no longer look quite the same; they look easier to solder, in fact. It didn't strand me then, but it is always possible. If it does strand me, I know what to do: move the ground strap back onto the battery with the toolkit screwdriver. ;)

I have made it to the promise land of >10 posts, so thanks.

damocles
 

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I just went with a straight digital Voltmeter which does the job for me. If the motor is off it shows lower than 12 v as I'm drawing from the battery, and when the motor is running it's above 12v as it's charging. Seems to do the job.

Mounted it on the panel just above the key. You might not be able to use this location if you have the handlebar cover/pad on the bike. I prefer the bare-bar style.

 

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This current-sensing resistor was purchased, not made by me. This project was put together 13 years ago, and used for 5 years on a previous bike. I believe the resistor was made by Vishay/Dale, but the present offerings no longer look quite the same; they look easier to solder, in fact. It didn't strand me then, but it is always possible. If it does strand me, I know what to do: move the ground strap back onto the battery with the toolkit screwdriver. ;)

I have made it to the promise land of >10 posts, so thanks.

damocles
Thanks for the info. I didn't realize you could buy something like that. 13 years is a pretty good reliability record!
 

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Discussion Starter #10
EDIT TO ORIGINAL POST: Never connect a wire to the positive battery terminal without having a fuse inline and close to the battery. Wire "C" should be fused but is not explicitly shown as such. Almost any value will do, as this wire carries microamps. The fuse is just there for safety... Sorry.

damocles
 
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