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Bluthundr31

Is there a way to test each fuse to determine amperage drawn on it?

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Bluthundr31

I might want to add "accessories" to an existing fused circuit but I would like to find a fuse that can handle the additional amperage before I go connecting wires to a circuit.

HOW DO YOU DETERMINE HOW MANY AMPS ARE BEING USED ON EACH CIRCUIT WHEN THE BIKE IS RUNNING & OUT ON THE ROAD?

 

I know I can put in an independent fused circuit for the accessory, but if I can tap into an existing circuit without overloading it, that might work out better.

 

Any electrical guru advice would be appreciated.

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AZgl1800

Well, first you need an ammeter capable of handling the current in that particular circuit.

 

Most of our little hand held DVMs only handle about 10 amps.

 

so, if the circuit is fused with a 10 A fuse or smaller, just simply remove the fuse, and bridge across its' terminals (socket) and read the circuit draw direct from the DVM/analog ammeter. 

 

I have both, analog and DVM, I use the one that suits my needs.

 

You will usually find, that the circuits are fused at roughly twice the current draw in the particular circuit.

They are there to protect the wiring from a direct short to ground.

 

Don't follow the temptation to just up the size of the fuse to handle the extra current you want. That fuse is designed to protect the small wires in that circuit.

 

If you need more current, say for an Air Horn ( 30 amps ), then you need to use a relay that gets its' power from an appropriate point.  ie, the Accessory fused terminal at the fuse block.  Make sure that the new relay is fused close to the power source, as you want to protect that new wiring from a direct short if that should happen.

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Bluthundr31

Thanks John, GREAT info!!  I'm using a Fluke 77/BN DVM multimeter and I saw the 10A and 300mA sockets but wondered if we could check the other fuses too with just the handheld DVM.  My *91 GL1500I needs a stereo upgrade (possibly with rear speakers), and a decent intercom set-up.  I'll be doing a bunch of research on how to best get 'er done, but then I stumbled onto this problem and was stumped for the correct answer.  

What is the point when a "relay" is needed?  Is it 30A or greater?

I'll keep in mind that the stereo and intercom set-up needs to be under 30A. 

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AZgl1800

the use of a relay is called for when the additional load you need to add will exceed the rating of the fuse in the circuit you are taking the power from.

Normally, we just use the "circuit used" as a trigger to operate a relay,

  • this could be because the control action might be turning lights on/off, powering an added on Air Horn and triggering from the OEM horn button circuit, or adding on extra Running Lights.... whatever the reason, the extra load is more than the OEM fuse can handle....

Never increase the fuse value beyond what the manufacturer has it marked for. The wiring attached to that circuit can't handle the extra load without getting hot and melting the insulation, or possibly burning up the wires.

 

And always make sure to use a fuse near the power source for the new Relay Controlled circuit. You don't want an inadvertent short to melt heavy wiring and causing a fire while you are rolling down the road.

 

When adding relays, it is best to get the power directly from a Battery terminal, or an added on terminal block that is connected thru a fuse to the Battery's positive terminal.  ( here, I used a 30A fuse to protect the terminal strip that I added to my bike. And I labeled each circuit with a tape label maker )

 

Nothing worse than finding owner added on wiring and you not having a clue as to what they are used for?

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AZgl1800

Here is an example of what I found, and how I cleaned up my bike's wiring.

 

The unmarked wires is the way I found a terminal strip block just free floating around, not secured in any way. It could have easily short circuited a hot terminal against a bare grounded point causing a fire. That added on terminal block did NOT have a fuse between it and the battery.

 

It does now, I used the same block but it is now secured where it can't get in trouble.

 

Click on any picture to see it in a larger view.

 

 

This is how I found the terminal block...

 

post-30-0-71208500-1500902953_thumb.jpg

 

 

This is how I rearranged things, added labels to the wires so I can see what they are for years down the road.  In this picture, the wire labeled "Air Horns" disappears under the seat, then to the rear of the bike. the PO installed the air horns behind the rear tire. And that wire just disappears to where?? I had to trace it out, tug and pull until I saw something move in the back of the bike, then traced that to the air horns. Add to that, the wire was NOT fused!!!  The picture is a bit fuzzy, the 3 labels are "Dist" ( Distribution Block ), "Trailer" ( hot 12v line to trailer circuits ), "Air Horn" as described.

 

post-30-0-63412800-1500903035_thumb.jpg

 

 

 

 

and here, I labeled more wires.  Note in this picture how I ran the Hot 12v wires going to the battery behind the battery bracket, and thru a piece of rubber hose to prevent them from getting chaffed by vibration over the years and bouncing down the highways.

 

post-30-0-06078600-1500903047_thumb.jpg

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Bluthundr31

Very cool information/pics.  You did a great job!!!  Sounds like a small-ish fused terminal block would be a decent source for the stereo and intercom wiring/power.  I'm still researching the "How-to" info for both projects, but I'll pick-your-brain when the time comes., , , , ,THANKS AGAIN

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Bluthundr31

For anyone who asked the same question that started this topic, , , The answer is YES (if you can pay $10.99)

Cen-Tech makes a 30 Amp automotive fuse circuit tester. I got one at Harbor Freight. It plugs into any ATC blade fuse slot and reads the amps being drawn on that circuit. You remove the good fuse from the fuse slot, plug it into the tester, then plug the tester into the slot where you just removed the good fuse. The bike will run/function normal. Now turn on the tester and the digital display shows the current draw. Accuracy is -+2%. Use it on any circuit up to 30Amps and you can verify accuracy for the 10A or less circuits using a DVM method. Handy little tool for the entire fuse block.

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AZgl1800

you might want to edit that last post,

 

it is NOT "Voltage Draw", it is CURRENT DRAW

 

 

I think the next trip to HF will see one of those current testers in my cart :)

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Bluthundr31

Thanks John for catching my "mis-speak".  its been corrected, sorry for the mistake.  The tool really seems to work well.  Used it on the car first and had good results.

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Swagonmaster

I read about an in interesting way to find amperage with a resistor. You put a one ohm resistor (of high enough rating that it won't fry itself) in the place of the fuse and measure the voltage drop across that resistor. Since volts divided by ohms equals the amperage it should give you a good idea of how much amperage you are pulling through that circuit. Just remember, that if there's more than one item being fed by the fuse you will see the total draw, not just the component of interest.

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Bluthundr31

Thanks, good to know swagonmaster. If I decide to "add" to my electrical needs, I'm going to want to know how many amps are already being drawn on an available circuit, so it's a good thing to know what the total draw is for the circuit being tested.

 

BTW, Welcome aboard! There's a great group of folks here who'll help you keep that wing on the road

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AZgl1800

just remember, that if that Resistor's value of 1 ohm is a significant overall value to the total normal resistance in that circuit, the load may well not perform properly.

 

IE, for a small load like a bulb, it probably won't have much of an effect, and the DVM would give a very good reading on the current flow.

 

but, if it is a motor circuit, or maybe a heavy airhorn that wants to pull 30 amps, that 1 ohm resistor is going to prevent you from getting a good reading.... the voltage drop across that resistor will be excessive, especially if the load has a very small internal resistance of something like 0.1 ohm...

 

when doing diagnostics, you must keep all things in perspective.

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