Power, VDC issues

[HB280ZT]

Hi All,

 

Well I am having a problem with the battery numbers that I am reading/datalogging on my PDA. What I mean by that is that as the car gets hot the voltage numbers drop, from 14 VDC to as low as 11 VDC. I know when it is low because the car runs like @#$% !

 

Now I have replaced the alternator and battery and checked all of my conections and I still have the same problem. I have looked at all of the MS V3 diagrams to see where the system gets its VDC reference but have not been able to find it, yet.

 

So if someone can tell me where datalog gets the VDC reference from for logging then I can start looking at possible components that could be causing this problem.

 

For more information about my system I am running everything through a relay board to my MS unit. The relay board is on the fender between the brake master cylinder and the water washer bottle and the MS unit is installed in the factory 280Z ECU mounting location.

 

So if someone can point me in the right direction that would be great.

 

HB280ZT

[Matt Cramer]

The VDC is from the 12 volt wire that supplies Megasquirt. Specifically, it's run through the R3/R6 circuit on a V3.0 board.

[z-ya]

Where is the relay board getting power from and what gauge wire have your for both ground and power to the relay board? You should have the relay board power tied to the battery., not another circuit or the starter/alternator.

 

Pete

[HB280ZT]

Thanks for the information.

 

As for where I am getting power it is coming directly from the battery via a fuse and 10 guage wire. The ground is also a 10 guage wire and it is grounded to the intake manifold with the injectors and such.

 

Here is a picture of my battery and basic wiring:

[z-ya]

Do you have a ground from the engine block to the battery? How many and what size ground wires do you have in the cable between the relay box and the Megasquirt?

[HB280ZT]

Yes I have a ground wire between the battery and the block and one between the block and the chassis and I think they are 2 guage. If you look at the picture the blue wires on the battery are the positive connections to the fuse blocks, alternator and starter. The brown wires are the grounds to the engine and chassis. Plus I have another ground wire, same brown wire between the engine and chassis on the other side of the motor around the A/C unit.

 

As for the wires between the relay box and the MS unit I used the wires that came as part of the MegaSquirt Wiring Bundle 12' that I got from DIYAUTOTUNE. Not sure if I added anything else as I built this setup 4 years ago now.

[HB280ZT]

HI All,

 

Well I am now having another problem with my new alternator, it was put in the car 4 days ago!

 

So the issue is it is putting out 15 VDC at idle and upwards of 18 VDC at speed. Well I promptly got off the road and disconnected the alternator and made it home on the battery. It showed 12.24 VDC on the PDA most of the way home and dipped down to 11.88 VDC by the time I got home.

 

So I will be off to the parts store (Advanced Discount Auto Parts) to have them check and hopefully replace the alternator for the 3rd time in 3 months, twice in one week. We will see if they give me a hard time again with the exchange.

 

Will keep you all posted on the results of my quest!!

 

HB280ZT

[softopz]

I dont know if this has to do with it but are you running the internally regulated alternator? If so did you do the proper splices putting diodes in the plug.