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VDST Battery voltage
- Thread starter TerryH
- Start date
It depends on where voltage is being measured, also. You cannot compare measuring it at the battery with measuring it somewhere else like at the ECU. There may be a voltage drop due to the resistance of the wires carrying the voltage as well as the draw of the components. It is normal.
I assumed that the aligator clips on the interface lead were for powering the interface and that the program displayed the battery voltage as read by the ECM.
I have verified the voltage at the battery with two digital multimeters and one analogue meter.
I have verified the voltage at the battery with two digital multimeters and one analogue meter.
If the VDST software is telling you what the ECU is reading for voltage then that would be where the difference comes from.
If you put a volt meter on the battery then you are measuring voltage "at the battery". The ECU on the other hand typically does not measure voltage "at the battery" as it is somewhere else. So what it does is display the voltage reading that results from measuring the voltage where it is. That reading will typically be lower then the reading "at the battery" due to resistance in the wiring harness causing voltage loss as well as the ECU and other components using electricity and causing a lower reading due to draw.
So, measuring voltage directly on the battery terminals will give you the actual voltage at the battery. Measuring voltage some where else, whether it is at the ECU or at the head light, will typically give you a lower reading due to the resistance of the wiring. And if that device is using electricity then the reading will be lower still. The ECU is telling you what the voltage reading at the ECU is. That is why it is different then the reading directly at the battery.
If you put a volt meter on the battery then you are measuring voltage "at the battery". The ECU on the other hand typically does not measure voltage "at the battery" as it is somewhere else. So what it does is display the voltage reading that results from measuring the voltage where it is. That reading will typically be lower then the reading "at the battery" due to resistance in the wiring harness causing voltage loss as well as the ECU and other components using electricity and causing a lower reading due to draw.
So, measuring voltage directly on the battery terminals will give you the actual voltage at the battery. Measuring voltage some where else, whether it is at the ECU or at the head light, will typically give you a lower reading due to the resistance of the wiring. And if that device is using electricity then the reading will be lower still. The ECU is telling you what the voltage reading at the ECU is. That is why it is different then the reading directly at the battery.
Brian UK
GT Reference
I would assume that the figures given in the OP were with engine stopped. What the ECU sees will depend on where in the system it reads the voltage and what load is on that particular part of the system as well.
It would be more relevent to give the voltages when the engine is doing 3k rpm.
It would be more relevent to give the voltages when the engine is doing 3k rpm.
A difference of more than 1.5volts between what is measured at the battery with a known reliable and accurate multimeter compared to what is displayed by the VDST software seems very excessive.
I know my electrical theory, I was hoping that someone else may have the same bike and the same software package who can compare figures.
We have done the testing with the bike running at 3,000rpm and the discrepency is still there.
I know my electrical theory, I was hoping that someone else may have the same bike and the same software package who can compare figures.
We have done the testing with the bike running at 3,000rpm and the discrepency is still there.
TerryH said:
VDSTS is a diagnostic tool, not a voltmeter. I don't expect the voltmeter function to be accurate as it depends on what the ECU "reports". You shouldn't expect that function to be accurate as there are too many factors involved in the result displayed. I've worked with Army TMDE equipment and I've never seen a DMM card in a computer to be an accurate measuring device. They are good for indications and trends only.
Stick with the DMM for accurate readings, and use the VDSTS for it's intended purpose. If the voltage display bothers you that much, change that channel (like you can do with your TV) to show something else and forget about it.
Some motorcycle ECU's have correction factors based on battery voltage as read by the ECU.
I'm not sure about the one in the Breva.
I am using VDST as a diagnostic tool which is it's intended use and expect the information displayed (including battery voltage as read by the ECU)to be correct or indicative of a system fault.
This is why I am asking the question if others have come across this discrepency.
This bike has displayed some difficulty in starting at times and I am exploring the possibility that it may be related to the ECU not reading the system voltage correctly.
I'm not sure about the one in the Breva.
I am using VDST as a diagnostic tool which is it's intended use and expect the information displayed (including battery voltage as read by the ECU)to be correct or indicative of a system fault.
This is why I am asking the question if others have come across this discrepency.
This bike has displayed some difficulty in starting at times and I am exploring the possibility that it may be related to the ECU not reading the system voltage correctly.
NOLAGuzzi
Cruisin' Guzzisti
- Joined
- Dec 5, 2008
- Messages
- 102
Others have said the same.TerryH said:
from https://www.guzzitech.com/forum/183/3022.html?start=60Eric said:
I would check my breva for you but I loaned my cable out. Mine is sometimes picky about startup too. I know it should not matter but I find that a little bit of throttle helps.
The software is not perfect (Do you know about the alfaline_0 channel for the TPS setting?) but it is what we have to work with.
Thanks NOLAGuzzi,
Yes I know about the Alfaline_0 channel.
The channel which displays 3.1 degrees for the assigned tps idle value after a TPS reset.
This particular bike has play at the pivot point of the linkage adjustment plates which causes the right hand throttle to vary along with the tps value with respect to the left hand throttle body.
To get it to throttle cleanly off idle I have had to find the mid point of the play for resetting the TPS.
I wonder if the voltage value diffence is due to a voltage drop from a diode junction within the ECU.
Yes I know about the Alfaline_0 channel.
The channel which displays 3.1 degrees for the assigned tps idle value after a TPS reset.
This particular bike has play at the pivot point of the linkage adjustment plates which causes the right hand throttle to vary along with the tps value with respect to the left hand throttle body.
To get it to throttle cleanly off idle I have had to find the mid point of the play for resetting the TPS.
I wonder if the voltage value diffence is due to a voltage drop from a diode junction within the ECU.
As I said earlier using software and a computer isn't a reliable piece of Test Measurement and Diagnostic Equipment (TMDE) simply because there is no way to calibrate the system against a standard. Proper TMDE can be calibrated against a standard and must be done periodically (6 mo, annually etc.)to remain in service for it's intended purpose. Since VDSTS and a computer cannot be calibrated, voltage type readings cannot be considered accurate.
I noticed the same thing on my Breva,I suspected the battery anyway and just fitted a replacement.However when you read the vdst instructions i'm sure it says to have at least 12.2 volts in the battery,surely you need to trust the vdst to give the battery volts not some spurious readings? I've used other diagnostic equipment in the past and the battery voltage reading has always been accurate,you shouldn't need a seperate meter when using diagnostic equipment...
From what I can see the VDST displays the information provided by the ECU and is not measuring the voltage itself.
I would assume that the ECU has been calibrated at some stage with regard to how it reads the bikes voltage as supplied at the ECU.
It's good to know that this is a common occurance and not just isolated to this instance.
Another point is that the ECU data could be transmitet in Hexadecimal , requiring conversion to decimal and also require a conversion factor for the displayed value in the software, eg. the decimal value divided by 10 or 100 as I have seen in another application of ECM and software. Hinting at a software formula error.
I would assume that the ECU has been calibrated at some stage with regard to how it reads the bikes voltage as supplied at the ECU.
It's good to know that this is a common occurance and not just isolated to this instance.
Another point is that the ECU data could be transmitet in Hexadecimal , requiring conversion to decimal and also require a conversion factor for the displayed value in the software, eg. the decimal value divided by 10 or 100 as I have seen in another application of ECM and software. Hinting at a software formula error.
At the end of the day the vdst states battery volts,if this is not displaying battery volts then change the display to show what is being read,if someone changed a component based on this equipment's reading would there? should there? be a comeback on the vdst team...is the tacho accurate,is the TPS correct?etc etc....
alwyn said:
When you find a Perfect world please let us know.
I've been a qualified veh technician for many many years,and in my experience diagnostic equipment has always been accurate,the vdst should be no different,if you pay good money you expect good products...not saying the vdst isn't good,but if there is a glitch it needs to be put right,or at least clarified....