Need Help Choosing Motor, Controller, etc.

[dcastillo]

(anyone feel free to correct me if Im wrong)
The contactor is usually a solenoid controlled by the controller, it connects the battery to the motor. This allows the controller to be in charge of connecting or disconnecting the motor (kinda makes it safer). I use a manual relay instead (giant push button).
Precharge resistor would go across the terminals of the relay (or contactor). The purpose is because the terminals of the controller have a large capacitor on them, if you directly connect a battery to it you will get a huge inrush current and arcing as the cap instantly charges. By having a resistor always there, it keeps the capacitor fully charged so when the batteries are directly connected, there wont be an inrush of current.

also see here
http://en.wikipedia.org/wiki/Pre-charge

 

[drm]

Attached is the simplified schematic from kelly without using a contactor, though I highly recommend at least a manually one so you can use a precharge resistor to avoid nasty sparks every time you plug in

I dont think that circuit shows a pre-charge resistor.

I also do not think that most of us think about the risk of what we are controlling (me included) should something in the circuit fail. I think it is easy to miss if you are used to gas karts. If the engine overspeeds or stops responding to your foot, then you can turn the ignition switch off right? Are we keeping the same sort of control for the electrics?

I worry about the controllers and components failing in a non-safe manner. If the something in output side of the controller shorts, I do not think the kill switch will help.

I would recommend a solenoid/contactor that is tied into the ignition switch. The mechanical disconnect switch is not a bad idea either and could be used if it is accessible from the driver seat.

 

[dcastillo]

I dont think that circuit shows a pre-charge resistor.

I also do not think that most of us think about the risk of what we are controlling (me included) should something in the circuit fail. I think it is easy to miss if you are used to gas karts. If the engine overspeeds or stops responding to your foot, then you can turn the ignition switch off right? Are we keeping the same sort of control for the electrics?

I worry about the controllers and components failing in a non-safe manner. If the something in output side of the controller shorts, I do not think the kill switch will help.

I would recommend a solenoid/contactor that is tied into the ignition switch. The mechanical disconnect switch is not a bad idea either and could be used if it is accessible from the driver seat.

I agree safety with electric karts is number one, I think you misunderstood my post (or I miss posted )

First you are correct, the schematic doesnt have the precharge res, I only posted it cause he thought the controller was overly complicated and I wanted to show him its actually very simple to use...

even a solenoid/contactor can fail. As a Electrical engineer, "I think" my push button is the safest thing possble. It is mounted on the positive side of the batteries, and positioned right under my steering wheel. As soon as you hit the "giant red button" you instantly disconnect power from everything and the kart dies.... no questions asked....

on top of that, I have a 2amp fuse to the controller power, an 80A fuse to the motor and a 100A fuse on every battery's positive terminal (making it impossible to short a battery and cause catastrophic issues, which is good cause I was the first one to short one of the batteries not my 6yr old)

Please be safe, electricity is DANGEROUS
-Danny

 

[drm]

RE: individual motors and controllers for each wheel without live axle

this could a good test for your team. set it up in a controlled environment and see what the actual conditions are. you could trim your speed input if it was there was consistent bias. for a 20mph kart, how would minor differences even affect the outcome?

understand the risks of what you are controlling.
- what happens if one wheel has traction and one doesnt?
- what happens in a turn (simulate a differential?)
- other??

this is where the fun comes in solving the problems.

 

[drm]

I agree safety with electric karts is number one, I think you misunderstood my post (or I miss posted )

First you are correct, the schematic doesnt have the precharge res, I only posted it cause he thought the controller was overly complicated and I wanted to show him its actually very simple to use...

even a solenoid/contactor can fail. As a Electrical engineer, "I think" my push button is the safest thing possble. It is mounted on the positive side of the batteries, and positioned right under my steering wheel. As soon as you hit the "giant red button" you instantly disconnect power from everything and the kart dies.... no questions asked....

on top of that, I have a 2amp fuse to the controller power, an 80A fuse to the motor and a 100A fuse on every battery's positive terminal (making it impossible to short a battery and cause catastrophic issues, which is good cause I was the first one to short one of the batteries not my 6yr old)

Please be safe, electricity is DANGEROUS
-Danny

just clarifying

sure contactors can weld but what is the likely hood of that vs. the controller? I dont know...

Cutting out the source like you have done is basic and will work no doubt about.

The point is, you evaluated the hazard and risk and mitigated it, and all should think about it as it is easy to forget.

 

[itsid]

I think dcastillos post is just the way to go. add big fuses into every sub-circuit that could fail,
that way you not only know you have a failure, but you can also trace where it originated.

contactors are (if chosen correctly) unlikely to weld;
Almost all controllers I've seen have some sort of fuse either attached to their power-in or embedded in the circuitry..
It's still good practice to add a fuse on your own, if you're unsure about the controllers fuse.

PWM controllers as we are talking about here, die on failure, it's impossible to have a motor running wild with a dead controller (it'll stop the motor!)
worst case it'll short internally and cook away all components.. still no way to short the batteries in a way that'll power the motor(s).

Anyways, since some controllers are at least "not cheap" it's better to protect it properly

I don't know if it's safer to use a push button than to use a std. contactor setup...
any of the two might fail/weld..
I don't know which one of the two is more likely to do so...
I think it all depends on size and capacity in the end.

Anyways, do what you can in regards of safety.. it's better to slightly overengineer safety gear than to discharge a single 12V 100 Amp battery through your body

If in doubt I'd say go for dcastillos set up,
it might be slightly overengineered, but at least it's as safe as possible.
And that's what you'd want.

'sid

 

[bdiermeier]

(anyone feel free to correct me if Im wrong)
The contactor is usually a solenoid controlled by the controller, it connects the battery to the motor. This allows the controller to be in charge of connecting or disconnecting the motor (kinda makes it safer). I use a manual relay instead (giant push button).
Precharge resistor would go across the terminals of the relay (or contactor). The purpose is because the terminals of the controller have a large capacitor on them, if you directly connect a battery to it you will get a huge inrush current and arcing as the cap instantly charges. By having a resistor always there, it keeps the capacitor fully charged so when the batteries are directly connected, there wont be an inrush of current.

also see here
http://en.wikipedia.org/wiki/Pre-charge

So the pre-charge resistor simply goes between the positive and negative of the battery disconnect? And just to clarify- the disconnect, like the one you linked, just goes in the positive lead between the battery and controller?

Also, what resistance and rating resistor do you recommend? I imagine it has to be very large wattage, but I'm not sure about how many ohms.

 

[dcastillo]

see attached... looks like they recommend a 1K 10W

where they are using a remote contactor, I am using a manual one... same concept though

 

[drm]

my kelly controller came with resistors and diodes but they are common items. mine also came with serial cable and null modem adapter.

 

[bdiermeier]

Hi guys! This project kinda stalled out for a while, but I'm finally getting back into it, and am about to order parts. I just have a couple questions before I order.

1. For the Kelly controller, can I get away with the small (50a?) size, or should I step up to the larger (100a?) size? It's a $40 difference, so I'd like to go smaller if I can.

2. Can anyone recommend good connectors for the batteries/motor? I will be using 4 gauge wire. It's kinda overkill, but it was given to me free so I'll use it.

3. How water resistant are the motors? Could they handle being used in a damp or snowy parking lot? (Assuming the controller is waterproof)

Thanks!

 

[bdiermeier]

One more question- would one band brake on the axle be enough, or should I use two?

 

[itsid]

one properly mounted well dimensioned brake should be sufficient.
Better stopping power isn't a bad thing though

'sid

 

[drm]

Whose project was this? Do you have a sketch that shows what you are concocting?

 

[bdiermeier]

Whose project was this? Do you have a sketch that shows what you are concocting?

It's my project, with some help from a friend. And what would you like a sketch of?

 

[bdiermeier]

Whose project was this? Do you have a sketch that shows what you are concocting?

Just for more detail it is a solid axle cart powered by two 1000w 36v motors. I plan to use (3) 12v batteries to power it. The motors will be controlled with a Kelly controller, still looking for advice on which one. Use will be mainly in parking lots. I don't know what other info I can give you, other than what is already in this thread.

 

[dcastillo]

if you are powering both motors with the same controller, then the 50A will not be enough...
And 4gauge wire is way... way... over kill.... even if its free I wouldnt use it... for one its hard to work with and the connector pricing goes through the roof and gets hard to find once you go past 10gauge... I switched for 10 to 8 gauge and it was a pain in the butt to find the connectors I needed and they cost a lot.... but Im running a 2KW motor...
You should use 10gauge, its good for solid 50 amps with higher spikes if needed...

 

[bdiermeier]

if you are powering both motors with the same controller, then the 50A will not be enough...
And 4gauge wire is way... way... over kill.... even if its free I wouldnt use it... for one its hard to work with and the connector pricing goes through the roof and gets hard to find once you go past 10gauge... I switched for 10 to 8 gauge and it was a pain in the butt to find the connectors I needed and they cost a lot.... but Im running a 2KW motor...
You should use 10gauge, its good for solid 50 amps with higher spikes if needed...

Thanks! And I'm probably sticking to my 4 gauge. Every electrical engineer I've talked to has recommended 4 gauge, so I guess better safe than sorry. So far connectors are not horribly overpriced, and it's plenty workable for what I'm doing.

 

[dcastillo]

thats fare, definitely better safe then sorry, but just so you know, 4gauge is rated for a constant current up to 135A....
But if you already know where to source connectors for a good price then go for it (heck, I may ask you in the future to find me some once I get a larger motor down the road )

 

[drm]

It's my project, with some help from a friend. And what would you like a sketch of?

it was a rhetorical question which is hard to gauge over the internets. It seems you ask a lot without much research. How do you plan to wire everything up? If you draw it out, you might answer future questions.

You can use whatever AWG you want but it is wise to protect it correctly to prevent fire. Your EE buddies should be able to help you out there.

As for connectors, I would use these my next go-around: http://www.powerwerx.com/anderson-powerpoles/powerpole-sets/

I use bluesea products and they have some reading material on wire sizing: https://www.bluesea.com/articles/1437

 

[dcastillo]

As for connectors, I would use these my next go-around: http://www.powerwerx.com/anderson-powerpoles/powerpole-sets/

thumbs up to the anderson powerpole connectors, those things rock. I got mine from McMastercarr. Perfect for 10awg (once you go larger the price jumps up )