pdm ground connection directly to battery negative?

[sinjin]

I have install other pdm (haltec, ecumaster, aim) but I am new to link and installing razor pdm first time. 

From razor user manual wiring instructions it says to connect both pdm positive and negative terminal directly to battery + and - ?

All other pdm I have used in past say to connect only + power to battery, and to connect - ground to engine just like I have been taught to do for ecu (star earth point concept).

Just wondering what is different with new razor pdm that recommends connect both + power and - ground back to battery?

Sorry for such basic question thank you for advice.

[aerace_fab]

You can ground it to the chassis with no problem. 

[BeallJK]

always wise to double check - 

confirmation: if you review Link's Razor Wiring Instructions item #3 it shows that grounding the negative posts to either battery negative or chassis.  

[sinjin]

Thank you I see that Link Razor Wiring instruction #3 show ground to battery negative terminal or chassis okay.   Two points I have question to be sure.

1. Is my understanding correct that best practice for ground pdm to engine star earth point and not to battery or chassis yes?

2. Builder of customer car connected razor pdm ground to battery negative terminal already, but I notice all other ground is using engine as star earth point (like ecu, alternator, cops).  Should I ask builder to move pdm ground to same engine star earth point same as other accessories?

[BeallJK]

If it was me I would keep it how the builder of the car constructed it.  Maybe you ask him why he hooked it up that way?

I wouldnt take on the liability of building the car - it doesnt sound like thats your role with the customer?  

If something does happen and grounds are wrong than it’s not your fault and you wont be held accountable to fix or pay for it.

just my 2cents…

 

[Vaughan]

On 9/30/2023 at 6:41 PM, sinjin said:

Just wondering what is different with new razor pdm that recommends connect both + power and - ground back to battery?

The Razor PDM is capable of H-Bridge control which requires being able to connect the high power outputs to both battery power and to ground. If the high power outputs are being used for H-Bridge control, especially for high current draw setups like the TurboSmart Wastegate, then it needs to be able to sink that ground current appropriately hence the requirement for a proper ground.

If you aren't using the H-Bridge functionality the ground is still required but the amount of current flowing through it is considerably less and so it is less important to provide a large high quality ground. Note that chassis or gearbox bellhousing/engine block are often suitable and equivalent to connecting directly to the battery negative as they are designed to have the starter current flow through them.

[sinjin]

6 hours ago, BeallJK said:

If it was me I would keep it how the builder of the car constructed it.  Maybe you ask him why he hooked it up that way?

I wouldnt take on the liability of building the car - it doesnt sound like thats your role with the customer?  

If something does happen and grounds are wrong than it’s not your fault and you wont be held accountable to fix or pay for it.

just my 2cents…

 

Yes my role for build is program the pdm and wire each circuit.  Builder fabricate mount and connect power and ground wire only.  He said he just follow instruction and connect to battery.  Funny thing he also thought it was strange manual did not recommend star earth point like other pdm.  I’m sure it will work but just wondering why razor different recommend from all other pdm maker for my own study?

6 hours ago, Vaughan said:

The Razor PDM is capable of H-Bridge control which requires being able to connect the high power outputs to both battery power and to ground. If the high power outputs are being used for H-Bridge control, especially for high current draw setups like the TurboSmart Wastegate, then it needs to be able to sink that ground current appropriately hence the requirement for a proper ground.

If you aren't using the H-Bridge functionality the ground is still required but the amount of current flowing through it is considerably less and so it is less important to provide a large high quality ground. Note that chassis or gearbox bellhousing/engine block are often suitable and equivalent to connecting directly to the battery negative as they are designed to have the starter current flow through them.

Thank you Mr Vaughan for explain.  

So if using bridge output on pdm we should be using battery earth point and not engine?

If so I assume using battery earth will always be best choice then and will allow for both bridge or low output?  Manual makes sense now. 

[Vaughan]

21 hours ago, sinjin said:

So if using bridge output on pdm we should be using battery earth point and not engine?

Either is fine, the important part is that if you are using the bridge you need to make sure that you have a ground that can deal with the current that the bridge will flow. i.e. the Ground wire size and location is appropriate, for example if using an E-Gate on the bridge then you would want to use a thick ground to somewhere near where the starter or alternator grounds.