Using Chassis for Negative Ground?

[powersupply]

So bottom line, no reason, really.

Isolation of wiring is given in any case.
Bearing point is no issue as I am mostly concerned about the battery to controller connection, which are all hooked to the main chassis from all the ebikes/scootesr I reviewed. And even if, a grounding connection can be made.

Galvanic corrosion would not be a concern here as I would use leaded wires and leaded shoes/connectors only.

Again, this is has been and is done with cars and trucks (24V and 48V) for ages.

Thanks for confirming this!

 

[footloose]

So bottom line, no reason...

Don't think so. Bottom line appears to be this. Low volt / amp systems could give you a nasty shock. But figure an ebike system at significant voltage and amperage.... Well, your heart kind of becomes the breaker in a geometry that is easy to short. Right?

The amount of power that can be dumped in an ebike short is kind of scary. I had a dead short once (my careless work) and it would have scared the piss out of me, except the fireworks were over before my bladder could respond :lol:

Better to isolate and control + and - as much as possible.

 

[alsmith]

What's so difficult about a 2 wire (+/-) system for simple electrics? It's more understandable with the more complicated systems of cars/motorbikes, but on a bike?

 

[teklektik]

So bottom line, no reason, really.
... I am mostly concerned about the battery to controller connection...
Thanks for confirming this!

So - let's see: a page of reasons and a de facto industry standard and you blithely dismiss it all as "no reason".
Remarkable.

I think you should do what you propose.

• 
  If your throttle sense wire chafes through, your bike will stop running.
  If your ebrake sense wire chafes through, your bike will stop running.
  If a phase wire chafes through - your controller FETs will blow.
  If a hall wire chafes through, the motor hall will blow or at best the motor will stop running.
  If your throttle power wire chafes through, your controller 5v supply will blow.
  If you stab yourself with a single loose strand of Vbatt+ that breaks the skin while you are in contact with the bike - well, it will be shocking - if across your chest your heart will clamp down before you can squeak.

But - you will have the pleasure of knowing you were smarter than the rest of the ebiking world (where these common failures would do nothing at all... )
And, of course, you will have saved 12" of wire.

 

[powersupply]

Hey guys, this is getting out of hand.

It was just a simple question on why in the ebike industry in particular the chassis is not used for conducting.

As mentioned many times, all cars I know of, some trucks, snowmobiles, and yes, even 96V 200A (or was it more?) forklifts do use the chassis for conducting current.
The mentioned reasons are no reasons but considerations.
If they really were reasons, no car, truck, forklift etc would ever use that method.

And I mentioned that the path from the battery to the contorller is important to me, not some tiny bulb at the edge of my scooter.

It is also is not about saving 12" of wire but actually saving some Ohms.
Though I thought this is obvious, but alas, there it is, in bold.

It is also not about the many ifs: what if a truck hits me? Again, these are considerations, but no reasons.

And it is definetly not for having the pleasure of knowing I was smarter than the rest of the ebiking world (whoever that is).
(though I must say I might reconsider that after reading some of these lines)
Who thinks and writes things like that?!?

JEEZ!

So bottom line, no reason, really.
... I am mostly concerned about the battery to controller connection...
Thanks for confirming this!

So - let's see: a page of reasons and a de facto industry standard and you blithely dismiss it all as "no reason".
Remarkable.

I think you should do what you propose.

• 
  If your throttle sense wire chafes through, your bike will stop running.
  If your ebrake sense wire chafes through, your bike will stop running.
  If a phase wire chafes through - your controller FETs will blow.
  If a hall wire chafes through, the motor hall will blow or at best the motor will stop running.
  If your throttle power wire chafes through, your controller 5v supply will blow.
  If you stab yourself with a single loose strand of Vbatt+ that breaks the skin while you are in contact with the bike - well, it will be shocking - if across your chest your heart will clamp down before you can squeak.

But - you will have the pleasure of knowing you were smarter than the rest of the ebiking world (where these common failures would do nothing at all... )
And, of course, you will have saved 12" of wire.

 

[Ypedal]

nobody does this, there has to be reasons..... if you really want to do it.. go ahead and let us know how it works out for you..

Consider charging, when you hook up your charger from the house AC, some chargers are not isolated.. exactly what havoc that could cause i'm not sure.. but i'm sure it's a factor. among others listed above.

 

[amberwolf]

It is also is not about saving 12" of wire but actually saving some Ohms.
Though I thought this is obvious, but alas, there it is, in bold.

A final thought from me: If it is about reducing resistance, then using the frame might not do that, for a couple of reasons. At least, not long-term, because of the last reason.

Typically copper is used in the wires, and that's a better electrical conductor than either steel or aluminum, which are the typical materials a frame is made of. However, the frame is probably a larger volume path than the wire, and thus is possibly (probably?) a lower overall resistance.

There will be at least two connection points where there was only one, before--the bolt point at the frame for the ground at the battery, and the bolt point at the frame for the ground of each other device, whatever it is. Each of those connection points may have multiple layers of various metals involved in the connection, if you use washers. The crimp or solder joint of the wire into the lug, then the lug to the washer(s), then the washer(s) to each other and the frame, and/or the screw if it is also conducting (if you use loctite or similar to secure the screw it may not do any conducting, or not as much). If the connection becomes even a little loose for any reason, at either of the two points, it has a higher resistance. It also allows moisture in between the metals, which could cause galvanic corrosion over time.


Niether one might be an issue for you, but it's another possible set of issues.

 

[kokopelli314]

If your bike uses a dc-dc converter, you risk frying it by grounding traction power to the chassis.

 

[alsmith]

Hey, go for it if that's what you think is best.

Please report back with your experiences, it will add to the knowledge of ways to do things, or possibly how not how to do things!

 

[jimnasium]

Hi, not to beat a dead horse, but I was wondering about this too. Mine is from a safety concern.

I see from many posts on this board pictures of the metal controller box, and the motor itself, strapped to the frame of the bike. The question is, what potential is the controller box at relative to Vbat(-)? Is it really floating? The FETs inside are bolted to the aluminum as a heat sink; I can't imagine that the circuit inside is totally isolated.

Further, the motor housing is attached to the frame through a bottom bracket. That too would be at some potential.

 

[middriveebike]

I think you should do what you propose.

• 
  If your throttle sense wire chafes through, your bike will stop running.
  If your ebrake sense wire chafes through, your bike will stop running.
  If a phase wire chafes through - your controller FETs will blow.
  If a hall wire chafes through, the motor hall will blow or at best the motor will stop running.
  If your throttle power wire chafes through, your controller 5v supply will blow.
  If you stab yourself with a single loose strand of Vbatt+ that breaks the skin while you are in contact with the bike - well, it will be shocking - if across your chest your heart will clamp down before you can squeak.

With so many risk associate with this single connection, what are the benefits?
With so many people willing to risk their balls blown doing this, there got to be a valid reason.
May be you can get some clean signal out of the switching DC converter inside the controller?

For me, risk way over weight benefit, and I will pass on this connection.

 

[alsmith]

Hi, not to beat a dead horse, but I was wondering about this too. Mine is from a safety concern.

I see from many posts on this board pictures of the metal controller box, and the motor itself, strapped to the frame of the bike. The question is, what potential is the controller box at relative to Vbat(-)? Is it really floating? The FETs inside are bolted to the aluminum as a heat sink; I can't imagine that the circuit inside is totally isolated.

Further, the motor housing is attached to the frame through a bottom bracket. That too would be at some potential.

It's your horse.

No-one else has shown an interest in doing this so please go and do it yourself, and report back after a years running.

 

[amberwolf]

The question is, what potential is the controller box at relative to Vbat(-)? Is it really floating? The FETs inside are bolted to the aluminum as a heat sink; I can't imagine that the circuit inside is totally isolated.

It is, unless there's a manufacturing defect, at least in all the controllers I've seen so far, both brushed and brushless, for bikes, golf carts, powerchairs, etc.

Further, the motor housing is attached to the frame through a bottom bracket. That too would be at some potential.

Not so far in the motors I've had--all are isolated, again unless there is a defect.

If there *was* a defect then grounding your frame would be a really bad idea, cuz it would fry things. Unless of course you have fuses in your circuits so they'll blow when a fault occurs, preventing voltages from being present on the casings/frame. But then, you'd also have no working electronics on the bike until you found and fixed the fault, so if you're in a situation where you *can't* just pedal home then you're gonna have to call someone for a "tow".

 

[EldRick]

The other big issue is that while 12v will never hurt you if you touch the wrong thing, 48v or higher at high amperage is lethal! A trivial mistake or a crash could be deadly.

 

[Toorbough ULL-Zeveigh]

As mentioned many times, all cars I know of, some trucks, snowmobiles, and yes, even 96V 200A (or was it more?) forklifts do use the chassis for conducting current.

It is also is not about saving 12" of wire but actually saving some Ohms.
Though I thought this is obvious, but alas, there it is, in bold.

both those are rongo.
where did you learn this from or is this just your interpretation for the reason?


i've never had the opportunity to troubleshoot a forklift so can't speak from direct experience.
but i can guarantee if i were to take a look i would find a big fat black wire running from the negative of the battery to the controller & motor.
the headlights in any car don't (or shouldn't) use the chassis as power return line.
even the radio has a black neg power line in addition to the either green or bare braid ground strap.


the only purpose for the grounding wire on a large vehicle is to prevent ground loops. (no bold required)
ideally there should be zero current in the ground line as well as the chassis.
an ebike is so small & power run so short, ground differentials don't present a problem.

 

[jimnasium]

Amberwolf, thank you for the thoughtful reply. That was exactly the information I was looking for. Cheers.