Sevcon Controller, what BMS to use??

johnnyz

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Im hoping someone can help me...I have a guy who wants to electrify his boat. I ordered 91 125ah BYD cells to make a 96 volt battery (33 kw) and he bought this kit. Its a Sevcon Gen 4. It has the motor, Controller, throttle, start button, kill button, Cooling plate for controller, plumbing, reverse/forward...but my question is; How the hell do you hook up a BMS to this?..it has a large contactor..and if there is a BMS made for this where does it go??...Ive done tons of ebikes, and my own projects, but this is something else..how would he charge this???....The cells have been arriving so im charging and balancing them, if anyone can help me it would be MUCH appreciated!IMG_20211201_132533R.jpg

Thanks

John
 

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Why would I what?...Of course this needs a BMS, especially with Lifepo4...Yes I want to make a 30s 3p Battery with ONE BMS, I just dont know which one, and if there is a compatable BMS with this specific Sevcon controller.
 
The balance leads obviously do, but how would the BMS 1) stop the charge when High voltage is reached and then stop the discharge when low voltage is reached?
 
The cheap BMS disconnects the charger when the battery is full and it disconnects the controller when the battery is empty.

The more expensive ones can give your a warning (I mean not a beep, I mean a signal via a bus system or a wire) before both states are reached, and there are also BMS out there wich can trigger external contactors for charging and discharging, the cheaper ones do this with Mosfets.
 
Thanks for the responses, but assuming that I dont know what I am doing because I have only dealt with ebikes, trikes, small motorcycles, now a Surron..and not a Sevcon controller and yes, a bank of batteries big enough to fry my ass...

I know that I need to get a BMS that will work via contactor probably for shutting off the Charging current and discharge but need something to reduce power levels when the cells get low, etc.

Ill contact the support team at Sevcon I guess
 
The sevcon controls the contactors itself, that has nothing to do with the bms.

Either get a stand alone bms to control the battery, or an advanced one that communicates on can bus with the sevcon.
I dont know how the later works, but maybe you can find some info in the manual.

How to charge? Get or build a suitable charger and connect to the battery I suppose? (trough the bms)
There is no charging trough the controller as far as I know if that is what you were after?
 
Thanks to j bjork...thats some of the answers I was looking for..I can get a BMS to control LVC and HVL but would like it to modulate the power as the battery gets low..just wasnt sure if it could be done through the Sevcon Controller..same as the Charger...

Will contact Sevcon and see what they have to say..

John
 
Like almost any other controller you set lvc in the controller.
Sevcon is a little more advanced than most, so you actually set two lvc and hvc:s and how you want the ramp up and down in current to be.
I think it is a better idea to start by reading the manual before you contact support.

The hvc and lvc in the bms is just there when something fails, not really to use for end of charge/discharge.
 
johnnyz said:
but need something to reduce power levels when the cells get low, etc.
That's what the controller does, via whatever settings it has for that.

I don't know what specific settings your Sevcon has available, but typically there will be settings in advanced controllers for limiting current draw from the battery below a specific battery voltage level, without the BMS communicating with it at all. Then other settings to simply shut it down below an even lower level, and possibly even a length of time it must remain below that level before it does so (so that short dips due to acceleration don't shut it off).



The BMS can't limit current or power except by completely disconnecting the battery from the load (via FETs or via contactor, or a shutdown line to the controller, etc).


A sophisticated enough BMS might be able to communicate specific info to a controlling system (be that a controller that understands this info, or a "head" unit that controls everything else and interprets this data and then tells the controller what to do), but I don't know much about what's available in that level of stuff. I would guess that there are large-EV BMSs that use CANbus and the like for this.



Regarding a BMS that can use a contactor, the large-EV systems are likely to be designed for this already.

A typical "cheap" BMS can be modified to do so. Instead of wiring the battery thru the FETs of the BMS, instead just wire it so it still uses teh BMS's shunt, but so the controller and system draw power from the other side of that shunt, rather than from the other side of the FETs beyond that shunt. If the shunt is on the wrong side of the FETs, you can simply use a busbar or other necessary wiring to "wire around" the FETs, so the shunt is still in play. That way the BMS can monitor current flow and do what it needs to, but isnt' using the FETs to control anything.


Then you can wire the gate control for those FETs to isntead control a driver for the contactor coil, and wire the contactor's contacts so they break whichever main power wires you need to for your system.

If the Sevcon is controling the contactor already, then if the Sevcon has an input line for enabling or disabling the system (which also shuts off the contactor), then you can use the BMS gate control to drive this input line. If it's the only input line, you can use logic circuits to combine the BMS input and keyswitch input and any other safety interlocks such that *any* of them that is in the "disable" state will disable the Sevcon. (I'd put lights on the logic so you can very easily see which ones are active and which are not, to make troubleshooting easy).
 
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