Need help with AMPS pull question

I mounted the airhorns on my 2007 rsv that my brother had mounted on his HD back in 1969. Back then he purchased SEARS air horn compressor and dual horns. I found them in a box recently, tested the compressor worked and mounted the whole thing on my RSV. I used the dedicated wiring harness with relay from Carbon One - great harness- designed for replacing the stock horn on the right side with a Stebel air horn- which pulls up to 20amp. The fuse in the harness is 20amp. These horns are so loud I can only TAP at the horn button and not lay on it. So I have probably tapped the horn button about 20 times in test. Today I needed to alert the rider ( friend) ahead of me that the passenger's scarf had come off her neck and was about to wrap in the rear wheel - that would not have been a pretty sight. I hit my horn button and silence. ( front left horn sounded but that isn't much) when I got home I immediately checked the 20 amp fuse and it was blown. I dropped a 30amp in the holder. I have an inline volt meter and at idle I see 13.5 v

when I hit the horn it drops to 12.5V

So here is the question: Old compressor obviously pulls more than 20amp, is it ok to go with 30 amp fuse or will that much draw hurt "something" - remember this is a dedicated power line direct off the battery using a relay.

Thanks for any guidance.

VentureFar...

Does your air compressor have a ground wire or does it ground at its mount.

If it has a ground wire is the mount insulated from the frame in case of a short?

Perhaps there is a short to the compressor body but your horn blasts were so brief

before to not blow the fuse. You could test continuity from the power in wire to the mount to see if you have continuity (ie low ohms....short circuit)

Does your air compressor have a ground wire or does it ground at its mount.

 

If it has a ground wire is the mount insulated from the frame in case of a short?

Perhaps there is a short to the compressor body but your horn blasts were so brief

before to not blow the fuse. You could test continuity from the power in wire to the mount to see if you have continuity (ie low ohms....short circuit)

Before I go to the garage let me explain that the compressor's built in metal mount bracket is spray painted black and the metal bracket I mounted it to is spray pained black and the spray painted bracket is attached to the factory painted passenger foot pad So no bare metal from the compressor is touching any bare metal.

What should I do to ground the compressor with everything painted

Thanks for your help.

VentureFar...

I'm suggesting you may have a short on the compressor so the body is live when

you relay sends power to it.

A bolt through the bracket is your ground path.

No tags or anything on the compressor showing normal current rating?

The label was old and impossible to read so I took it off and painted the body.

This is a diagram of what I know. Please guide me on what to check.

I have a DVM with ohms and also continuity tester.

The compressor bracket will beep when using the continuity tester to frame ground

http://img.photobucket.com/albums/v468/ihavethespirit/pbVentureFar/C249CD23-317E-43D1-9191-1339748FEEC9_zps378figit.jpg

Thanks again for guidance.

VentureFar...

Maybe what is trying to be explained is, even though you have ground at the compressor, it is not enough so to speak for the amount of amps being used. Just for giggles connect and extra ground to the bolt on top of the trans if your working on that side of the bike where the right side OEM was.

I just went thru horn He!! on mine. Ended up being a combo of things to include a bad connector @ the relay. I would say 30a for the horn would be a bit much. But if its on a dedicated feed thru a relay its feasible.

OK to answer your question about using a 30 amp fuse, if you have a direct short the 30 amp will also blow. AS far as hurting the compressor, the compressor will only draw what it draws, supplying the compressor with extra amp capability will NOT increase what it draws. Before you go 30 amp, how about trying a 25 amp?

Now, the only possible potential damage will be to the battery itself. If you are using the stock lead acid battery it will eventually be weakened from hitting the horn. The drop you saw is about right, so you can imagine what continuous usage is doing something to the battery. I highly recommend using an AGM battery which can handle a stronger load with ease...

Very concerned your picture shows .1 ohms across the wiring points. Looks like one side shows to ground and the other side to +12v. Ohms Law states that this is 120 Amps on a 12 volt system.

The quality of your meter can easily effect this reading. You could also wire a meter with at least a 30 Amp scale in series with the compressor and read amps directly.

I would recheck this reading, and I would expect about .8 ohms or a little higher, which would equate to 15 Amps on a 12 volt system.

Next I would check both wiring points to the compressor frame. Assuming the frame is not designed to also be ground (should not be if it has dedicated ground wiring point). The expected reading would be very high (5M ohms+) to infinity.

Bkuhr

You wrote

You could also wire a meter with at least a 30 Amp scale in series with the compressor and read amps directly.

I am using a good digital volt meter.just to clarify:

Do I take the ground lead off the compressor and attach the meter leads in that line?

Thanks all

VentureFar...

Bkuhr

You wrote

You could also wire a meter with at least a 30 Amp scale in series with the compressor and read amps directly.

 

I am using a good digital volt meter.just to clarify:

 

Do I take the ground lead off the compressor and attach the meter leads in that line?

 

Thanks all

 

VentureFar...

Yes, you could take the ground lead off the compressor, attach Amp meter plus to the compressor, and amp meter negative to the removed ground lead or frame ground.

Ensure leads are in the correct AMP ports of the meter, and Amp scale set to highest possible.

I would agree with testing ohms on the unhooked compressor from the + terminal to the body of the unit for a short.

Carefully inspect your power in connection too....any possibility the + wire terminal is touching the compressor body?

Although the compressor wouldn't spin with the volt meter in line, the readings varied from 11 ohms to 18 ohms when I press the horn button.

Does that sound right?

Thanks again for the help. M

VentureFar...

Although the compressor wouldn't spin with the volt meter in line, the readings varied from 11 ohms to 18 ohms when I press the horn button.

Does that sound right?

 

Thanks again for the help. M

VentureFar...

A volt meter must be hooked in parallel. The Amp meter is hooked in series (in line). A Ohm reading 'in line' is useless as you are applying external battery across the ohm scale, and stand a very good chance of damaging the meter.

First lets test your Amp meter. Set meter leads in the ports for amps- red lead usually has a different port for amps than normally used for volts and ohms. There may be 2 different ports, one for amps and one for mA milliamps. Put red lead into Amps port. Black lead usually remains in the same common port used for volts and ohms.

Now put meter in highest Amp scale, and touch leads to a 9v transistor radio battery, Red to battery plus and black to battery negative. Meter should show 2-3 amps. If not the internal fuse in the meter may be blown, and would need replacement. This fuse is used just for Amps readings, and the meter would still work volts and ohms with the blown fuse.

Assuming the meter is ok, the compressor should turn with the meter in series and set up for amps, if it turns without the meter.

A volt meter must be hooked in parallel. The Amp meter is hooked in series (in line). A Ohm reading 'in line' is useless as you are applying external battery across the ohm scale, and stand a very good chance of damaging the meter.

 

First lets test your Amp meter. Set meter leads in the ports for amps- red lead usually has a different port for amps than normally used for volts and ohms. There may be 2 different ports, one for amps and one for mA milliamps. Put red lead into Amps port. Black lead usually remains in the same common port used for volts and ohms.

Now put meter in highest Amp scale, and touch leads to a 9v transistor radio battery, Red to battery plus and black to battery negative. Meter should show 2-3 amps. If not the internal fuse in the meter may be blown, and would need replacement. This fuse is used just for Amps readings, and the meter would still work volts and ohms with the blown fuse.

 

Assuming the meter is ok, the compressor should turn with the meter in series and set up for amps, if it turns without the meter.

Ok idiot alert. Stand back it might be contagious !

This time I did as you said. MOVED the red lead to the 10amp fused hole. Took a smoke detector down and checked the Battery at 2.75 amps.

This is a fluke 77 multimeter.

The 10A hole says "10A fused. "

Is it going to blow when I NOW properly check the compressor??

Thanks

VentureFar...

As we are suspecting compressor is pulling more than 20 amps, then yes- the 10amp meter fuse will blow. Best not to do this test.

Would be better if you could get a DC amp clamp.

verify with ohms compressor coil resistance across both wire connections, and wire connections to compressor case, all with compressor unwired.

1st short your leads to each other and measure ohms, likely around .1 ohms. This is lead resistance. Subtract this reading from readings taken on the compressor.

I would agree with testing ohms on the unhooked compressor from the + terminal to the body of the unit for a short.

 

Carefully inspect your power in connection too....any possibility the + wire terminal is touching the compressor body?

No ohm change from zero ohm test compressor body to either electrical connection on the compressor body. There is no marking for plus or minus and I have switched plus and minus many times when hitting it with jumper cables before I mounted it.

Is there a "for sure" plus and minus?

VentureFar...

As we are suspecting compressor is pulling more than 20 amps, then yes- the 10amp meter fuse will blow. Best not to do this test.

Would be better if you could get a DC amp clamp.

 

verify with ohms compressor coil resistance across both wire connections, and wire connections to compressor case, all with compressor unwired.

 

1st short your leads to each other and measure ohms, likely around .1 ohms. This is lead resistance. Subtract this reading from readings taken on the compressor.

Ok I am brave and have two meters so I went for it.

1st left lead off and compressor spun. Took a moment but registers 30.0 Amps.

2nd switched "power" leads on the compressor and tested again. Compressor spun and Fluke said 30.0 amps.

Guess it pulls 30 amps when I hit the button.

Actually that is no shock because if you stand next to the bike when I hit the horn you KNOW this thing is pulling Amps to be THAT loud.

So based upon confirmed current draw of 30 amps. Obviously momentarily. I won't. "Lay" on the horn - don't need to - it wakes the dead- is it looking like a 30 amp fuse and a light horn finger will all work together???

Thanks so much all your guidance.

VentureFar...

No ohm change from zero ohm test compressor body to either electrical connection on the compressor body.

 

VentureFar...

Does this mean you read zero ohms from terminal to body, or no ohms (infinity) from terminal to body?

As for specific + and - terminals, it is possible it does not matter. and chance of posting a picture? Sometimes a specific + terminal would be brass colored and a - terminal silver colored.

Ok I am brave and have two meters so I went for it.

 

1st left lead off and compressor spun. Took a moment but registers 30.0 Amps.

2nd switched "power" leads on the compressor and tested again. Compressor spun and Fluke said 30.0 amps.

 

Guess it pulls 30 amps when I hit the button.

Actually that is no shock because if you stand next to the bike when I hit the horn you KNOW this thing is pulling Amps to be THAT loud.

 

So based upon confirmed current draw of 30 amps. Obviously momentarily. I won't. "Lay" on the horn - don't need to - it wakes the dead- is it looking like a 30 amp fuse and a light horn finger will all work together???

 

Thanks so much all your guidance.

 

VentureFar...

Looks like you really are pulling 30 amps- Is this a Train Horn:thumbsup2:

Fuse should be rated slightly higher than the load. I would install a 35 amp fuse.

Now you have to ensure you have the proper wire size for a 30 amp load, or the wire could overheat and melt or burn.

For a 30 amp load you need at least 12awg wire, and consider using 10awg wire. Also need to ensure the relay you are using is rated for 30 amps, or the contacts could fuse closed, leaving the horn blaring.

Make sure the big wire is used from battery to relay, relay to compressor +, and compressor - to frame.

Thanks. Checking on the size of the wires.

Will photo the install tonight.

Thanks

VenturFar...

A lot of usefull info posted but the simple question (is it safe to go to a 30 amp fuse?) has not been answered. The straight answer on this is most likely not. The reason is simple. The fuse should not be able to carry a higher amp load than the wiring it is supposed to protect. If the wiring is of a heavy enough gauge to handle 30 or more amps than it is not a problem. But if the wiring is too light then instead of the fuse blowing the wiring will overheat and possibly cause an electrical fire.

The compressor may be drawing to much because it is defective or it simply may be a heavy duty compressor which requires 30 or more amps to operate.

If it is the later simply

1. Run a heavier gauge wire directly from the battery through a 35 amp fuse (if that is what is needed) to a relay.
   
2. Then from the relay to the compressor.
   
3. Use the bikes existing horn wiring to activate the relay.
   

Ooops The thread #20 just before mine did answer the situation quite well. I must have overlooked it some how.

Agreed.

I am checking with carbon one who made the harness to confirm guage and relay.

If not then I will rewire. Carbon one's harness is designed for stiebel horn and not they monster I have

Thanks for the advise.

Would suck to be on the side of the road with horn blaring and bike on fire.

VentureFar....safely

Gauge is almost always marked on the wiring EG: awg12. And the relay will usually have its amp rating marked on it.

FYI metric wiring is often marked in Millimeters which can be converted to Gauge thickness VIA a chart easily found on the internet