Measuring electrical load

kerrizor

Premier Member
IBR Finisher
#1
So I was thinking about upping my aux lights from the current Denali D4 -> ...something bigger... and recalled some chatter that even the mighty GSA couldn't power _everything_.. and I realized that despite my comfort with wiring and whatnot, I don't actually know how to find the capacity of my 1250GSA's system, or what it's current load is. Anyone have any resources that they can point me towards?

(I know this is a bit of a general question.. sorry!)
 

Stephen!

Flivver Flyer
Premier Member
IBA Member
IBR Finisher
#2
Three-phase generator with 510 Watt nominal power.

Without knowing its base load and adding all the loads of all the extra stuff you installed, about the only way I can figure to get your total load is to connect an amp meter in series with your battery and do the math.

510 watts @ 14 VDC (Typical automotive alternator output) comes to just around 36 amps.

If you measure the amps going through your system at full load and subtract that from total available (36), you will have a number for what remains for more goodies.
 
Last edited:

mess533

Ron Messick, Independence, MO IBA#598
Premier Member
IBR Finisher
#4
Amperage is measured in line with your circuit. Either with an Amp clamp or meter in line. Do you have a meter picked out?

I'm nearly certain I have a meter at home. I'll look when I get there in a few hours. I'll mail it to whoever needs it.
 
Last edited:

kerrizor

Premier Member
IBR Finisher
#5
Amperage is measured in line with your circuit. Either with an Amp clamp or meter in line. Do you have a meter picked out?
Of course I don't own a clamp meter any more ("I'm not doing anything where I'd need this thing... might as well downsize!") - I assume the line to the starter motor would be a good single-line spot to test.
 

mess533

Ron Messick, Independence, MO IBA#598
Premier Member
IBR Finisher
#6
If you were to test the lead going to the starter you would get the amperage being used by the starter. Sadly to get whole system amperage readings you'll need to test a circuit at a time. Or place the clamp on every lead leaving the battery. Being careful to not overload the fuse in the meter.

Looked in the garage and I no longer have my meter. Maybe thats why my old neighbor stopped talking to me before they moved?
 
Last edited:

mess533

Ron Messick, Independence, MO IBA#598
Premier Member
IBR Finisher
#8
My apologies, I tried taking amperage readings on my bikes. Both operate on a can-bus network as does yours. Being on a network within the bike many signals are on each wire. The meter I suggested is looking for a single signal. You'll need an osciliscope to get amperage readings. I hope you haven't gone ahead and purchased any meters. Again, I apologize!!!
 

kerrizor

Premier Member
IBR Finisher
#9
My apologies, I tried taking amperage readings on my bikes. Both operate on a can-bus network as does yours. Being on a network within the bike many signals are on each wire. The meter I suggested is looking for a single signal. You'll need an osciliscope to get amperage readings. I hope you haven't gone ahead and purchased any meters. Again, I apologize!!!
No worries! That's kind of what I was afraid of - having to find a NERD to beat up for his oscilliscope. I'll grab his slide rule while I'm at it! ;)

..but seriously, I suspect going the other direction and just mathing out the load of each accessory is a decent enough approach here, and will get me close enough in the end.
 
#10
On an old school bike, I was able to pull the main fuse and insert an amp reader I got from Harbor Freight to read the amp draw. (Amp reader has connection for the main fuse) With it installed I could see how many amps the bike itself required run at 5000 RPMs. Subtracting the output of the alternator, let me know how many amps I had for other uses.

-Mark
 

rneal55555

Premier Member
IBR Finisher
#11
You should be able to find the base load in a Repair Manual or ask in a BMW Tech forum somebody will know. then just add what you've added for a total.
 

EricV

Premier Member
IBR Finisher
#12
@kerrizor - My google fu is usually pretty good, but I can't find any re-occurring value for the wattage overhead on the R1250GSA.

Do you have a voltmeter installed that you can monitor? In simple terms, if you see that dropping below 12.4 V or so, you're in the danger zone and below 11.8 or so some bikes won't fire the injectors. You sometimes end up coming to a stop at the gas station only to discover your battery is too dead to start the bike.

Obviously, it would help to know if you have XXX watts to play with, left over from the 510 the bike puts out. But you could also run a static wattage test in the garage, at idle and at the RPM that stabilizes max output, then start plugging lights into leads off the battery until you see it go below 12V at the RPM where it's normally stable at max output of the stator/alternator. If you've got enough stuff laying around to increase the wattage draw, it will give you a general baseline.