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Hugues
27 August 2012, 2343
As much as I understand the way of working and purpose of a ground for an electrical appliance at home (if the high voltage slowly leaks to the frame of a washing machine for example, you'd want this leak to be flushed to the ground and not build a high voltage on the frame where someone could be zapped).

But then for a motorbike, in the instruction manual of my BMS for example, i'm asked to connect it to the ground. And I understand by ground they mean the frame of my bike. But this one is not connected to the earth due to the isolation of the tires, so what is the mechanism involved here ? How can this prevent a high voltage building up on the frame ? Just because it's a huge mass of metal ?

And then, in another thread, i'm bench testing my battery pack, BMS and DC-DC converter. I think N&V told me to connect my BMS ground to the DC-DC converter ground (because i don't have the frame with me yet). Here the DC-DC converter is just a tinny piece of metal compared to my bike frame. How about I just connect the BMS ground to a small copper bar ? What is the difference between grounding this way and grounding to the DC-DC ground. Surely I'm missing something here.

I like to understand what I do and why I do it and not just do it because it's written to do so.

SplinterOz
28 August 2012, 0014
Ground in this sense is just terminology for the -ve side of you 12 volt system.
For an EV the frame should NOT be used for "ground" or "earth" of either voltage system if it can be avoided.

Hugues
28 August 2012, 0409
Ground in this sense is just terminology for the -ve side of you 12 volt system.
For an EV the frame should NOT be used for "ground" or "earth" of either voltage system if it can be avoided.


??
from the Orion BMS wiring manual:
http://www.orionbms.com/resources/
"Ground Lug
A ground lug is provided on the outside of the enclosure. The BMS MUST be grounded to a vehicle chassis or Earth ground (if stationary) for proper electrical noise rejection. "

I thought I also read this in other manuals and forums.

You mean by "Ground in this sense is just terminology for the -ve side of you 12 volt system" that my ground is just the negative, usually black wire of my components ?? I'm a little surprised here.

Let's see what others have to say, because i'm quite surprised to read this, but why not.

picaroon
28 August 2012, 0504
Its annoying that the word 'ground' can mean different things in electronics!

It sounds like the 'ground' lug on your bms is there to prevent static electric, or any other voltage leaks perhaps, damaging sensitive cicuitry inside. So connecting it to an earth spike in the ground while stationary is probably what you would do if using when bench testing or maybe when used with solar charging perhaps. I would still keep it separate from your house earth. When its fitted to your bike frame it will allow static charge to dissipate, your frame must be isolated from anything electrical though.

EDIT:I was mistaken, the frame can be also used as 12v ground.

Hugues
28 August 2012, 0557
.. So connecting it to a earth spike in the ground while stationary is probably what you would do if using when bench testing or maybe when used with solar charging perhaps. I would still keep it separate from your house earth.
All clear, that's probably what i will do while on the bench in the garage (earth spike)



When its fitted to your bike frame it will allow static charge to dissipate, your frame must be isolated from anything electrical though!

This is less clear now. Wouldn't the user manual of my DC-DC converter tell me to connect it's ground to the frame too ? I will check this tonight of course but..
And I've got shielded cable for my HV lines, i have to connect the shield to the frame. So only the BMS should be connected to the frame ? nothing else ?

picaroon
28 August 2012, 0634
I'm sure you can still bolt your dc-dc converter to the frame as it would most likely be isolated. But I agree with Splinter that I wouldn't use the frame as my 12v -ve like is traditionally used by ice bikes or cars. It probably can be done, it just feels safer not to do it and run extra cables for the 12v -ve for the lights, horn etc....

frodus
28 August 2012, 1116
There's absolutely no reason you cannot or should not ground the 12v side of an isolated dc-dc converter to your chassis. In fact the Orion and elithion require you to do so. You could run with a ground only connected individually to each device bit then you get into some nasty ground loops. You absolutely should ground at one single point with each device having its own run to that point.

The Orion is designed so that it can check isolation between the pack and the 12v ground. Its got features in place that check this. If you don't have things grounded to chassis, your chassis could potentially be "hot" and you wouldn't know it because it isn't grounded to -12v.

If your dc-dc is isolated you've got no issue with accidentally touching it. All cars have 12v ground running through it and some motorcycles do (although its easier to run a harness due to location of the lights and rubber dampeners isolating the lights.

I've got experience with both the Orion and Elithion systems.

The only time you should not connect the dc-dc to the frame is when you have a non-isolated dc-dc which essentially puts pack ground on the frame. Touch the pack positive while you work and you might get zapped a little with pack voltage.

With an isolated dc-dc there's no issue. You can touch pack positive and lean on the chassis and unless the dc-dc failed, you're fine. But with the Orion and Elithion, you'll know if there's an isolation issue because the bms will fault.

And chassis ground in the case of EV's means the 12v ground or -12v. Do not connect this to earth ground of a house.

Hugues
28 August 2012, 1259
Ok
My dc-dc converter is from Sevcon, fully isolated, specs here :
http://www.electricmotorsport.com/store/pdf-downloads/sevcon_dcdc.pdf

They don't mention anything about ground actually, unlike the Orion BMS. So I understand I will be able to bolt its case/heat sink to my frame , but while on the bench, I'm not going to connect the 12 v output negative to the ground of my BMS , right ?

frodus
28 August 2012, 1354
-12v is ground. The negative of the 12v dc-dc is always connected to ground on the Orion. Thats my point. They're one and the same and they're connected together. Its not ground as in house ground. Terminology is one thing. The other thing is whether you want your 12v ground connected to your chassis. If you do not you miss out on that test that the Orion can check for isolation between pack and your 12v system. If you connect you will have no issues because its an isolated dc-dc.

Do this:

For the ground (pins 11 and 12) of the bms connect it to the -12v of the dc-dc converter. This is sometimes referred to as 12v common. Connect the positive 12v to charge power when charging and to ready power when discharging. Always on is always connected to a 12v source.

Sounds like you may be having some trouble understanding how it all goes together. Have you drawn a schematic first? Do that before you hook anything up and post on your build thread.

I've offered help before due to the complexity of your system. Offer is still open. The differences between your system and my own is minimal.

Athlon
28 August 2012, 1502
Generally in safe EV there are 4 different electrical potential

the + main pack
the - main pack
the + 12V system
the - 12V system

the latest one ( - 12V system) can be connected to the chassis frame , in this case you call the frame "Ground".

The high voltage main pack wires MUST BE AWAY from the chassis , any high voltage wire touching any metal inside the car or the bike can create a lethal situation.

DC-DC must be ISOLATED so the high voltage and the 12V never share the ground.

Hugues
29 August 2012, 1206
I read the Orion BMS wiring manual once more and I realise I may have confused some of you with this Ground thing.

On first page of the manual it is written in red that the ground lug of the BMS (picture below) must be connected to the bike frame, to avoid static electricity build up.

3544

I've started to update my wiring diagram to include the BMS and DC-DC converter, here:
3545

It's clear that 12V+ from DC-DC goes to port 1 of BMS (always ON) and with a switch to port 2 (READY mode).
Then the 12V- of the DC-DC goes to port 11 or 12 of the BMS (called ground, and I don't know if these ports are connected internally to the ground lug).

But no where in the manual of the Orion BMS it is mentioned to connect port 11 and 12 (12V negative ground) to the bike frame, as suggested by some of you above. The BMS seems to be able to detect leak into the frame through the ground lug maybe ? I checked continuity between ground lug and port 11 and 12 and there is none.

So I will contact Orion to set this straight, 12V negative has to be connected to bike frame or not. I'll post their reply here.

Hugues
29 August 2012, 1208
I read the Orion BMS wiring manual once more and I realise I may have confused some of you with this Ground thing.

On first page of the manual it is written in red that the ground lug of the BMS (picture below) must be connected to the bike frame, to avoid static electricity build up.

3544

I've started to update my wiring diagram to include the BMS and DC-DC converter, here:
http://www.gliffy.com/pubdoc/3515533/L.png

It's clear that 12V+ from DC-DC goes to port 1 of BMS (always ON) and with a switch to port 2 (READY mode).
Then the 12V- of the DC-DC goes to port 11 or 12 of the BMS (called ground).

But no where in the manual of the Orion BMS it is mentioned to connect port 11 and 12 (12V negative ground) to the bike frame, as suggested by some of you above. The BMS seems to be able to detect leak into the frame through the ground lug maybe ? I checked continuity between ground lug and port 11 and 12 and there is none.

So I will contact Orion to set this straight, 12V negative has to be connected to bike frame or not. I'll post their reply here.

frodus
29 August 2012, 1220
Sounds like they test for voltage between that ground lug and pack positive. Double check.

Hugues
30 August 2012, 0916
Got a mail from Chris at Orion BMS,
not mandatory to connect 12V negative of Orion BMS to frame but if one wants to use the frame leak detection features then 12v negative must be connected to frame.
He says it's also good to connect it for noise reasons.

case closed.

they could have mentioned it in their manual i guess, or maybe i missed it.

thanks for your patience.

Allen_okc
30 August 2012, 1205
i pretty much isolated the battery pack and the 12 volt system from the frame - it required double the amount of wiring...

sysTom
07 January 2013, 1832
Very elucidating thread. I am retrofitting a 2009 GPR-S with a newer BMS from Elite Power Systems. The tech there also confirmed that -12V could and perhaps should be connected to the chassis. But, of course, you don't want BATTERY+ or - anywhere near chassis, for safety reasons we must keep them isolated. Here is my dilemma: My new DC-DC converter is a four-lead device, internally isolated. The legacy DC-DC converter (or 'inverter' as it says on the legacy schematic) is a three lead device! It shares ground! I see Battery- is electrically connected to everything on the 12V system. Zirg! It appears I will have to rewire a goodly portion of the bike. So much for getting this up and running quickly.

Athlon
07 January 2013, 1855
just one notes about your wiring , kill switch and intertia switch should be in series with key switch.

If you just cut the contactor a very high voltages spike will flow trough KSI wire (all the current that was flowing in the contactor will try to flow in the KSI) and this will destroy the controller.

Emergency switch should always turn off the controller from KSI and later (few millisecond) the controller will disconnect the contactor once all the mosfet are in the off state , if you just open the contactor with the mosfet in on state the full current will try to flow inside the electronic board.

If you want the controller ON but the bike unable to run you should use the interlock input , this will allow you to have the controller on and ready for everything BUT to run the bike , interlock is also used for the sidestand switch as safety feature for not running the bike with the sidestand open

Also I see your menu button directly connected to the 96V , any wire outside the battery box should always use 12V ( the best is to have also KEY KSI under relay) , water can easily get into pushbutton and the mix between water , 96V and human is not a good mix.