1985 LTD Electrical System DC requirements

Reference information handy in one place - part numbers, aftermarket equivalents, circuit diagrams, and more
  • Sponsored Links
Post Reply
User avatar
Posts: 1501
Joined: Wed Nov 18, 2015 12:44 pm
Location: Victoria, British Columbia, Canada
Motorcycle: 1985 GL1200 LTD (X2), 2008 GL1800 (sold)

1985 LTD Electrical System DC requirements

Post by Rednaxs60 » Wed Feb 28, 2018 8:04 pm

I have mentioned in some of my posts that the electrical system ampere requirements are more important than the electrical system voltage requirement. I mention this because it is an accepted fact that the output from the alternator unit is expected to be maintained at ~14.0 VDC regardless of the electrical system load. It is the electrical system load in amperes that fluctuates and causes the RR to allow more or less current into the electrical system to maintain the voltage at ~14.0 VDC.

I have a 3 wire external alternator installed (55 amps) and IMHO, it is more effective in reacting to the varying load demand than the OEM 3 piece alternator unit.

In this regard I purchased a clamp meter that measures direct current. Had one that I thought did but found out it only measured AC. The readings are an indication only and I do understand that the accuracy of my meter may not be up to that required by NASA, but I now have an appreciation for the ampere requirements of the system, and roughly how the load distribution is.

Measured the DC in the electrical system on my '85 LTD here in Victoria this afternoon. The key here is the voltage indicated on the dash voltmeter staying constant at ~14.0 VDC.

On start and with fast idle (1150ish RPMs) and 14.0 VDC display on the dash voltmeter: 17 amps
At fast idle and 14.0 VDC on dash voltmeter: fluctuate between 15.5 amps and 17 amps - indicates battery has been topped up
At fast idle and 14.0 VDC on dash voltmeter with both sets of driving lights on: 20.5 amps
At fast idle and 14.0 VDC on dash voltmeter with both sets of driving lights on and rad fan as well: 23.5 amps (have a manual switch for rad fan)
At fast idle and 14.0 VDC on dash voltmeter with both sets of driving lights, rad fan, and heated clothing: 29.0 amps

Considering the alternator units on these bikes is capable of a max ampere output of approximately 35 amps, these readings indicate to me that there is more than enough power for the bike operation as designed and intended by the OEM without any additional loads added by the owner such as driving lights, and heated clothing.

The '85 LTD FI and '86 SEi FI bikes have a 30 amp circuit connected to the battery terminal of the starter solenoid. Took a reading from the wire to the starter solenoid and it displayed ~10.5 amps. Took a reading on the wire/cable from the starter solenoid to the battery it registered ~3.0 amps. This indicates to me that the battery is taking 3.0 amps and 7.5 amps are going back into the electrical system for bike operation, and that 7 amps are going into the electrical system through the ignition switch. I did another check of the amperage from the alternator and it was still at ~17 amps.

I think this reading to the starter solenoid is quite important from an understanding perspective. I have mentioned that I do not subscribe to the philosophy of connecting additional loads to the battery positive terminal. If the amperage going from the power junction to the starter solenoid at ~10.5 amps was connected to the positive terminal of the battery, the battery would be continually in an overcharging state even though there are other loads needing some of this power. It would be nice to think that the power would be discriminating and go to where it is needed and not affect any other component, but since there is no control over this the battery would be seeing more power than is intended.

I also connected my heated clothing into the electrical system. The heated liner increased the electrical system load by 5 to 6 amps – considerable actually.

Turned on the signal lights, and the electrical system current fluctuated approximately 1 amp - bounced around actually. Not too concerned because the signals are short duration use.

I annotated a schematic with some arrows for current flow and letters for current at various locations. This schematic is when the engine is started and at idle.

Here is the schematic:

Point A is the one connection where the total electrical system load is represented. In the case of my bike at idle it is approximately 17 amps (goes up progressively as loads are added to the electrical system) - good number to start with.

Point D is approximately 10 amps of which this is split such that point C has a current flow of approximately 7 amps and point B (battery) has a current flow of approximately 3 amps. Point C is a 30 amp circuit that is connected to the starter solenoid battery terminal and is apparently only on the '85 and '86 FI models. This further indicates a best practice of not connecting directly to the battery positive terminal as there would be 10 amps at the battery instead of 3 amps - the short battery cable connection to the starter solenoid does do a specific design service - ensures the battery is a load device on the system, not a power junction, and prevents overchargin ghte battery. For those who do not want to do a lot of wiring change, a best practice of connecting extra circuit(s) at the the battery terminal of the starter solenoid should be preferred instead of at the battery positive terminal.

Point F is the DC flow into the system, as does point B. This is at start and when the battery supplies supplemental power to the electrical system. This is for a short duration. The DC flow will primarily be to the starter solenoid, not from it.

Point G indicates the current flow from the alternator unit.

The remainder of the 17 amps at point A goes through the ignition switch at point E and is approximately 7 amps.

In regards to the above, I would submit that an initial wiring upgrade to ensure more effective and efficient electrical system operation, and to ensure longevity of the alternator unit and other electrical components is to relocate the RR sense wire to point A – power junction. This eliminates the voltage drop in the electrical system wiring and the probability of overtaxing the alternator components because of the voltage drop that is sensed from the electrical system. A relay would have to be installed to ensure power is only to the RR when the key is turned on.

The second change would be to connect a 12/10 GA wire from the power junction to the starter solenoid to replace the dual red and red/white wire to the starter solenoid. This gauge of wire would be sufficient for the amount of current flow from the power junction to the stater solenoid.

The third change would be to install a new RR that uses the MOSFET technology. This can be a shunt or series type RR. These RR units do not have a sense wire, but instead use the RR output wire for the voltage reference check. The best replacement is a series RR, but these units are not as inexpensive as the shunt type RR units with the MOSFET technology.

The fourth change would be to install an external alternator driven off the end of the crankshaft providing the owner with a number of alternator ampere sizes to choose from. A 40 ampere rated alternator would be more than sufficient for everyday use.

Thought I'd share some of my findings.

Just MHO and YMMV.


"When you write the story of your life, don't let anyone else hold the pen"


Post Reply