Current draw and alternator loading
Discussion
OK..... Done a couple of longish trips in the GTR over the last week. 200 miles to brooklands wings and wheels, the requisite high speed runs on the runway, and 200 miles back again.
There was a bunch of traffic including stop start for 40 minutes or so. Despite fairly warm weather (for the UK) the car could sit with the fans on indefinitely without a problem. However I did notice that with the a/c on the idle dropped and so did the battery volts. I was expecting this due to the direct load from the a/c pump, but the voltage drop was more than I expected.
So got to wondering which element was driving the big drain on the battery.
So just did a few tests in the garage. With no engine running I looked at the voltage drop caused by each of the elements.... Assuming voltage drop is proportional to current this seems a fair indication of load.
I saw...
Radiator fans (2 high power pacet profane) 0.4v drop
A/c fan (under rear clip) 0.2v drop
Heater blower setting 1 0.8v drop
Heater blower setting 2 1.1v drop (0.3v more than setting 1)
Heater blower setting 3 1.5v drop (0.4v more than setting 2)
A/c compressor clutch (just the actuator) 0.4v drop
So I am surprised by a couple of things.....
The heater blower on setting 1 draws twice the current of two rad fans.... And on setting 3 nearly 4 times the current !!!!!
Also just the clutch on the a/c compressor draws the same as the two rad fans !!
Interested if anyone else is surprised or can challenge my conclusions or have any measurements themselves..... I had always assumed the rad fans would be the biggest draw.
Stu
There was a bunch of traffic including stop start for 40 minutes or so. Despite fairly warm weather (for the UK) the car could sit with the fans on indefinitely without a problem. However I did notice that with the a/c on the idle dropped and so did the battery volts. I was expecting this due to the direct load from the a/c pump, but the voltage drop was more than I expected.
So got to wondering which element was driving the big drain on the battery.
So just did a few tests in the garage. With no engine running I looked at the voltage drop caused by each of the elements.... Assuming voltage drop is proportional to current this seems a fair indication of load.
I saw...
Radiator fans (2 high power pacet profane) 0.4v drop
A/c fan (under rear clip) 0.2v drop
Heater blower setting 1 0.8v drop
Heater blower setting 2 1.1v drop (0.3v more than setting 1)
Heater blower setting 3 1.5v drop (0.4v more than setting 2)
A/c compressor clutch (just the actuator) 0.4v drop
So I am surprised by a couple of things.....
The heater blower on setting 1 draws twice the current of two rad fans.... And on setting 3 nearly 4 times the current !!!!!
Also just the clutch on the a/c compressor draws the same as the two rad fans !!
Interested if anyone else is surprised or can challenge my conclusions or have any measurements themselves..... I had always assumed the rad fans would be the biggest draw.
Stu
If you want to measure "voltage drop" from the current flowing, you need to measure over a fixed length of the wiring, and not just the voltage across the battery.
Too many factors change the system voltage to make it a reliable indicator of SoC or Current output.
I'd be amazed if the cabin HVAC blower was more powerful than two Rad cooling fans. Typically, cabin fans are around 60W (~5A) and Rad Fans 80 to 120W (~8A to ~10A).
If the system voltage is falling during idling with a high consumer load (AC, Fans etc) then your alternator is NOT able to output sufficient charge (and you are discharging your battery stored energy, rather than having the alternator supply the required power). One option is to use a smaller puller on the alternator to increase it's performance, as a typical alternator has an output function like this:
Too many factors change the system voltage to make it a reliable indicator of SoC or Current output.
I'd be amazed if the cabin HVAC blower was more powerful than two Rad cooling fans. Typically, cabin fans are around 60W (~5A) and Rad Fans 80 to 120W (~8A to ~10A).
If the system voltage is falling during idling with a high consumer load (AC, Fans etc) then your alternator is NOT able to output sufficient charge (and you are discharging your battery stored energy, rather than having the alternator supply the required power). One option is to use a smaller puller on the alternator to increase it's performance, as a typical alternator has an output function like this:
Mr Pid said:
OK..... Done a couple of longish trips in the GTR over the last week. 200 miles to brooklands wings and wheels, the requisite high speed runs on the runway, and 200 miles back again.
There was a bunch of traffic including stop start for 40 minutes or so. Despite fairly warm weather (for the UK) the car could sit with the fans on indefinitely without a problem. However I did notice that with the a/c on the idle dropped and so did the battery volts. I was expecting this due to the direct load from the a/c pump, but the voltage drop was more than I expected.
So got to wondering which element was driving the big drain on the battery.
So just did a few tests in the garage. With no engine running I looked at the voltage drop caused by each of the elements.... Assuming voltage drop is proportional to current this seems a fair indication of load.
I saw...
Radiator fans (2 high power pacet profane) 0.4v drop
A/c fan (under rear clip) 0.2v drop
Heater blower setting 1 0.8v drop
Heater blower setting 2 1.1v drop (0.3v more than setting 1)
Heater blower setting 3 1.5v drop (0.4v more than setting 2)
A/c compressor clutch (just the actuator) 0.4v drop
So I am surprised by a couple of things.....
The heater blower on setting 1 draws twice the current of two rad fans.... And on setting 3 nearly 4 times the current !!!!!
Also just the clutch on the a/c compressor draws the same as the two rad fans !!
Interested if anyone else is surprised or can challenge my conclusions or have any measurements themselves..... I had always assumed the rad fans would be the biggest draw.
Stu
Part 2:There was a bunch of traffic including stop start for 40 minutes or so. Despite fairly warm weather (for the UK) the car could sit with the fans on indefinitely without a problem. However I did notice that with the a/c on the idle dropped and so did the battery volts. I was expecting this due to the direct load from the a/c pump, but the voltage drop was more than I expected.
So got to wondering which element was driving the big drain on the battery.
So just did a few tests in the garage. With no engine running I looked at the voltage drop caused by each of the elements.... Assuming voltage drop is proportional to current this seems a fair indication of load.
I saw...
Radiator fans (2 high power pacet profane) 0.4v drop
A/c fan (under rear clip) 0.2v drop
Heater blower setting 1 0.8v drop
Heater blower setting 2 1.1v drop (0.3v more than setting 1)
Heater blower setting 3 1.5v drop (0.4v more than setting 2)
A/c compressor clutch (just the actuator) 0.4v drop
So I am surprised by a couple of things.....
The heater blower on setting 1 draws twice the current of two rad fans.... And on setting 3 nearly 4 times the current !!!!!
Also just the clutch on the a/c compressor draws the same as the two rad fans !!
Interested if anyone else is surprised or can challenge my conclusions or have any measurements themselves..... I had always assumed the rad fans would be the biggest draw.
Stu
Redone the measurements with a voltmeter on the battery (2 decimal places) rather than using the readings from the stack.
Rad fans 0.3v drop
A/c fan 0.15v drop
Heater blower setting 1 now 0.1 v drop
Heater blower setting 3 now 0.15 v drop
A/c clutch now 0.15 v drop.
This makes much more sense and goes to show that,depending on the cars wiring, you can't really trust the cockpit volt meter.
Stu
ive been having the same problem with mine.
an auto electrician has done a few checks and couldnt find anything wrong other than lack of relays.
we found the ignition switch was burnt again!! the white wires at the back of the switch have been hot causing a voltage drop comparing across the battery and across the fuses(nice test for you to try.
we have wired in a relay to take the loading as the msd etc when turned on arcs inside the ignition switch and causes alot of heat.
also we found the twin fan set up needs a 40 amp fuses not 30... although the 30 amp fuse doesnt blow it gets mega hot
also have you a battery cut off switch.,.. if so try readings again with this removed!!
the other thing to ask is how old is your car.. they updated the wiring loom in the early 2000 as the main cable from alternator to starter was too small.. might be worth check which you have
its strange you are experiancing the same thing ive been speaking to Richard and Andy about most of this year... is it just SBC? or are others here experiancing it?
dom
an auto electrician has done a few checks and couldnt find anything wrong other than lack of relays.
we found the ignition switch was burnt again!! the white wires at the back of the switch have been hot causing a voltage drop comparing across the battery and across the fuses(nice test for you to try.
we have wired in a relay to take the loading as the msd etc when turned on arcs inside the ignition switch and causes alot of heat.
also we found the twin fan set up needs a 40 amp fuses not 30... although the 30 amp fuse doesnt blow it gets mega hot
also have you a battery cut off switch.,.. if so try readings again with this removed!!
the other thing to ask is how old is your car.. they updated the wiring loom in the early 2000 as the main cable from alternator to starter was too small.. might be worth check which you have
its strange you are experiancing the same thing ive been speaking to Richard and Andy about most of this year... is it just SBC? or are others here experiancing it?
dom
As above, there is a considerable drain on heater fan speed 3,
I have also changed out the ignition switch due to heat damage and intermittent connection ( I was having to "jiggle" the key sometimes for the ignition to stay on!
All in all the alternator I have performs fine and I have no worries about draining the battery with the car running, though I'd think twice about running the heater fan on speed 3 in traffic with A/C, lights and rad fans running.
I have also changed out the ignition switch due to heat damage and intermittent connection ( I was having to "jiggle" the key sometimes for the ignition to stay on!
All in all the alternator I have performs fine and I have no worries about draining the battery with the car running, though I'd think twice about running the heater fan on speed 3 in traffic with A/C, lights and rad fans running.
F.C. said:
As above, there is a considerable drain on heater fan speed 3,
I have also changed out the ignition switch due to heat damage and intermittent connection ( I was having to "jiggle" the key sometimes for the ignition to stay on!
All in all the alternator I have performs fine and I have no worries about draining the battery with the car running, though I'd think twice about running the heater fan on speed 3 in traffic with A/C, lights and rad fans running.
I have the original ignition switch (mini?), spotted the heat during my build and 'sunk' the heat out to the chassis via a thick alloy mounting plate. Touch wood I have had no heat related issues with the switch.I have also changed out the ignition switch due to heat damage and intermittent connection ( I was having to "jiggle" the key sometimes for the ignition to stay on!
All in all the alternator I have performs fine and I have no worries about draining the battery with the car running, though I'd think twice about running the heater fan on speed 3 in traffic with A/C, lights and rad fans running.
V8Dom said:
.....we have wired in a relay to take the loading as the msd etc when turned on arcs inside the ignition switch and causes alot of heat........
Are you referring to the MSD ignition?There should be 2 supplies into the MSD. One is a permanent supply ideally direct from the battery but could be from the starter solenoid. It should be a quite heavy duty wire. The second is a trigger supply from the ignition which is just to tell the unit to switch on so should take next to no current.
Steve
the two wires out of the ignition which dont go to the fuse box are 1 to the fuel pump switch and 2 the wiring diagram says coil but if msd is fitted it wires into there..
yes msd has proper feed, but if turning the ignition on and off, the draw or jump of the msd, fuel pump switch , the supply to fuse box is too much for a little old 50 year old ignition switch.... this ignition switch, i hope has been replaced on the new updated Evo car, as i feel isnt fit fora 100k car ad in the 6 years ive owned mine, im now on my 3rd???,,
i have wired in a 70 amp relay, for now, however after a long chat with the auto electrician, we will be making alot of changes to the standard wiring loom over winter as its lack of relays and over heating of some of the wires is a fire waiting to happen. running a car with only 6-8 fuses also doesnt leave room for inprovement so we will be fitting a second fuse box in the other side hatch for accessories, etc
the other updates ive done in the past which has been discused on here is the addition of a relay for the lights.... as again that switch although rated at the amps needed of the headlights burns out and mine melted part of the loom too last time
yes msd has proper feed, but if turning the ignition on and off, the draw or jump of the msd, fuel pump switch , the supply to fuse box is too much for a little old 50 year old ignition switch.... this ignition switch, i hope has been replaced on the new updated Evo car, as i feel isnt fit fora 100k car ad in the 6 years ive owned mine, im now on my 3rd???,,
i have wired in a 70 amp relay, for now, however after a long chat with the auto electrician, we will be making alot of changes to the standard wiring loom over winter as its lack of relays and over heating of some of the wires is a fire waiting to happen. running a car with only 6-8 fuses also doesnt leave room for inprovement so we will be fitting a second fuse box in the other side hatch for accessories, etc
the other updates ive done in the past which has been discused on here is the addition of a relay for the lights.... as again that switch although rated at the amps needed of the headlights burns out and mine melted part of the loom too last time
Edited by V8Dom on Monday 7th September 23:03
Very timely as I was going to post a similar query. Mind you with an LS7 track car.
I'm also finding a significant voltage drop with the lights, AC, an occasionally fans.
The main draw is with the AC on with the blower going full. My first thought was it was the AC clutch and fan but the blower fan was not in the mix and I need to look at that.
What I have done is put in a 150A relay to take the wimpy key out of the equation. This may exasperate the voltage drop but the key is very much a hazard.
What i have found is that there is a a very small wire (one easily joined with a yellow crimp connector) from the alternator into the harness.
I'll replace this with "cable" to the starter solenoid terminal block to ensure that full power gets to the battery to keep it topped up as a "hot" start without the start battery connected is a bit of a struggle.
I'm also finding a significant voltage drop with the lights, AC, an occasionally fans.
The main draw is with the AC on with the blower going full. My first thought was it was the AC clutch and fan but the blower fan was not in the mix and I need to look at that.
What I have done is put in a 150A relay to take the wimpy key out of the equation. This may exasperate the voltage drop but the key is very much a hazard.
What i have found is that there is a a very small wire (one easily joined with a yellow crimp connector) from the alternator into the harness.
I'll replace this with "cable" to the starter solenoid terminal block to ensure that full power gets to the battery to keep it topped up as a "hot" start without the start battery connected is a bit of a struggle.
Couple of things to add here...
Fitting my fuel on demand unit reduces the current draw from the HP fuel pump from a whopping 10A down to about 2A at idle and around 3A during cruising. Really provoking it and I am yet to draw above 5.5A and then only for a short period (at least on the road!).
I notice that full beam is a huge drain - practically I guess you never have full beam on sitting idling (and even less likely to have them in conjuntion with cooling fans and air con on full).
Mark
Fitting my fuel on demand unit reduces the current draw from the HP fuel pump from a whopping 10A down to about 2A at idle and around 3A during cruising. Really provoking it and I am yet to draw above 5.5A and then only for a short period (at least on the road!).
I notice that full beam is a huge drain - practically I guess you never have full beam on sitting idling (and even less likely to have them in conjuntion with cooling fans and air con on full).
Mark
Interesting one in the garage yesterday afternoon.
I thought I didn't have a battery type cable between the alternator and the starter solenoid, but my memory isn't what is once was... nice high quality battery size cable between them...
Double checked the terminals and resistance, all was tip top.
Next I hooked up the digital multi-meter (DMM) to the battery (BAT), on top of the analog Ultima dash volt gauge (UVG) and my MoTec dash voltage output MDV (this one is regulated to give a clean smooth voltage). I do have an hand held digital Amp-meter but for some reason it's not working.
The battery is a Red Top 60 that is a few years old that was fresh off the trickle charge. No additional start battery was used.
No load engine NOT running
BAT 12.9
UVG 12.6
MDV 12.9
Engine NOT running full electrical load
BAT 11.5
UVG 11.0
MDV 11.2
Engine running No load
BAT 14.1
UVG 13.8
MDV 13.1
Engine running full electrical load (a little more RPM needed due to the load but still about 1100)
BAT 13.8 (double check and same at starter solenoid)
UVG 12.8 then drops to 12 and a bit after a while and back up to 13.2 when blower/AC switched off)
MDV 13.1
Now tough one.. Engine started (when warm) with full electrical load. I have to say it did protest a bit but it did start after a few "churns"
BAT 10.3
UVG about 9
MDV 10.1
Just looking at BAT (the MDV is quite stable) it appears to me that the battery is pretty good and the alternator is providing a good stable voltage and amperage output.
The questions is why does the UVG show a lower voltage (some times significantly) than the BAT.
Two theories are, 1 Calibration of gauge, 2 there is a voltage drop due due to the newly installed master relay.
Number 2 seems more likely as I don't recall a low voltage reading before however, the relay for "Switched items" is rated to 150A which should be more than sufficient (the starter & alternator does not run though this relay, they wired with substantial battery cable through the electrical cut off switch and a current limiter)
Another thought is that the battery feed wire to the relay needs to be beefed up.
I thought I didn't have a battery type cable between the alternator and the starter solenoid, but my memory isn't what is once was... nice high quality battery size cable between them...
Double checked the terminals and resistance, all was tip top.
Next I hooked up the digital multi-meter (DMM) to the battery (BAT), on top of the analog Ultima dash volt gauge (UVG) and my MoTec dash voltage output MDV (this one is regulated to give a clean smooth voltage). I do have an hand held digital Amp-meter but for some reason it's not working.
The battery is a Red Top 60 that is a few years old that was fresh off the trickle charge. No additional start battery was used.
No load engine NOT running
BAT 12.9
UVG 12.6
MDV 12.9
Engine NOT running full electrical load
BAT 11.5
UVG 11.0
MDV 11.2
Engine running No load
BAT 14.1
UVG 13.8
MDV 13.1
Engine running full electrical load (a little more RPM needed due to the load but still about 1100)
BAT 13.8 (double check and same at starter solenoid)
UVG 12.8 then drops to 12 and a bit after a while and back up to 13.2 when blower/AC switched off)
MDV 13.1
Now tough one.. Engine started (when warm) with full electrical load. I have to say it did protest a bit but it did start after a few "churns"
BAT 10.3
UVG about 9
MDV 10.1
Just looking at BAT (the MDV is quite stable) it appears to me that the battery is pretty good and the alternator is providing a good stable voltage and amperage output.
The questions is why does the UVG show a lower voltage (some times significantly) than the BAT.
Two theories are, 1 Calibration of gauge, 2 there is a voltage drop due due to the newly installed master relay.
Number 2 seems more likely as I don't recall a low voltage reading before however, the relay for "Switched items" is rated to 150A which should be more than sufficient (the starter & alternator does not run though this relay, they wired with substantial battery cable through the electrical cut off switch and a current limiter)
Another thought is that the battery feed wire to the relay needs to be beefed up.
Could it be that the further from the battery the gauge is, and therefore, lower in the power pecking order, the lower the reading you will get!
I do question how often you will start the car with everything switched on. Rad fans probably but I switch everything else off until the car is running.
Paul
I do question how often you will start the car with everything switched on. Rad fans probably but I switch everything else off until the car is running.
Paul
My Ultima gauge reads 16v with the engine running and normal electical load (even fans when running don't cause a drop). The only time it dips below 16v with the engine on is with the aircon on at the same time as full beam and/or the fans running. But no lower than 13.5-14v even then.
With engine off and no load it reads around 13.5v or so.
Mark
With engine off and no load it reads around 13.5v or so.
Mark
Indeed, a further look at the voltage to and from the relay with the DMM and then as mentioned the UVG.
The start with ALL electrical loads on was simply a max stress test to see if the system would cope.
Normal procedure is for all loads off and wait till all pumps have cycled and use an auxiliary "start" battery. Spins over and starts like a treat.
The start with ALL electrical loads on was simply a max stress test to see if the system would cope.
Normal procedure is for all loads off and wait till all pumps have cycled and use an auxiliary "start" battery. Spins over and starts like a treat.
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