Alltrax 4834 and me0909 wiring set up help.

[fehlbergo]

Hi guys,

I'm currently working on an electric motorcycle prototype for my final year uni project. My frame is well on it's way and I have nearly all the components I need to put together the electrical and drive side of things. I'll run you through what I have and what I'm planning for the electrics, because I'm really not sure if it's correct or the safest way to do it.

Motor - Motenergy me0909
Controller - Alltrax 4834
Battery - LiFePO4, 48v, 20AH with BMS
Magura throttle 0-5k ohm
Battery kill switch - 300A
Fuse - 300A

I found a wiring diagram online and modified it with the set up I currently have.

As this is a proof of concept motorcycle with a custom made frame I won't even be thinking of trying to register it, so having a proper ignition switch and working accessories aren't a major problem. With the current set up I would plan to use the kill switch as the ignition switch.

One question I have is; do I need a contactor with the precharge resistor and diode? I've seen this set up a lot and I'm wondering if I need it, or if it would greatly increase the safety of my components?
Something like this

Thanks

 

[amberwolf]

That seems a pretty small pack for a motorcycle, as many such packs are only able to sustain 1C (so 20A for this pack), with short peaks of 2C (40A for this pack), so some questions:

Battery - LiFePO4, 48v, 20AH with BMS

How much continuous and peak discharge current is the BMS rated for?

How much c & p discharge current is the pack itself rated for?

How much c & p current is the controller rated (limited) for?

How much c & p current do you expect to actually pull during use?

 

[fehlbergo]

Yeah, it's a tiny pack. Won't get a lot of run time, but I'm not super fussed about that at the moment. I got the components off a previous student, so I'm not 100% on the details of the battery and BMS. I can probably find that out if it's critical?

The controller has a current limit of 300A @ 30s-2min. 200A @ 5min. 135 @ 1hr.

I plan to baby the bike a bit. It's a cargo motorbike with an experimental front steering, so I don't really want to go that fast... Attached render bellow.

What are the risks of running the system without a contactor though? Am I more likely to fry the BMS or controller?

Cheers

 

[amberwolf]

Cant' see anything useful about the front end in that render. :/

The controller has a current limit of 300A @ 30s-2min. 200A @ 5min. 135 @ 1hr.

If in use you actually pull that kind of current from that battery, I'd expect the BMS to either shutdown the system every time you touch the throttle from a complete stop, or blow up, depending on how fast it reacts and how well it's made.

If the BMS doesn't have a current protection on it's output and a way to shutdown the pack on overcurrent, drawing that kind of current from that small a pack is probably going to kill it pretty quick, unless it's made from A123 cells.

If it's a typical generic pack made from 18650 cells, I wouldnt' expect it to last much beyond initial testing, if it survives that far, based on what I have seen of a couple of Vpower/CammyCC packs, adn stuff posted about other types here on ES. :/

What are the risks of running the system without a contactor though? Am I more likely to fry the BMS or controller?

I think the BMS is more likely to be fried by the excessive current this system will be capable of pulling, if it actually does end up pulling that much.

Contactor is used to prevent welding your switch shut if you have to disconnect under load (assuming you use a contactor designed for that purpose).

Usually needing to disconnect under load means the cotnroller already fried. which usually results in shorted FETs whcih in a brushed motor system often means full power to the motor with no control of it.

A contactor *might* mean you could shut it down with the switch that way, while attempting to do so directly with the switch might not work as it might arc across the switch contacts and weld them together.

But a "jumper plug" you can yank out of the system would still work even if siwtch or contactor fails, and it's pretty cheap to do. See a recent thread by Spinningmagnets about an open source switch which includes some discussion on that.


Precharge you can do without a contactor--just look up the word here on ES, by topic title, and display by topic, and there should be plenty of examples.

 

[fehlbergo]

Cant' see anything useful about the front end in that render. :/

This might be clearer~ Not sure if it has an actual name, but I've just been calling it double knuckle steering. Kind of a bastard cousin of centre hub steering. I will be using a cable steering system to transfer the inputs from the handle bars/steering column to the front wheel.

XYZ Cargo Bicycle uses the same system

I was told that the pack was made by a reputable source with good cells. But I'm not really sure what the means :?

The exact same set up - motor, batteries, controller and throttle - I'm using has been used by another (different) student in the past, but he used a contactor and no kill switch or fuse...

So I'm assuming the batteries and BMS can handle it. The controller is programable, so I could drop the output stats down to be more gentle.

Thanks for explaining the purpose of contactors btw. I didn't really get what they were for, but it makes sense now. Cheers.