DIY Electric Car Forums banner

1 - 9 of 9 Posts

·
Registered
Joined
·
16 Posts
Discussion Starter #1
Thinking of using two main contactors both with pre-charge relays. One controlled by the Curtis controller and the other controlled by the Emus BMS. Placing the Curtis controlled power contactor on the positive cable and the Emus BMS power contactor on the negative cable.

Any thoughts, good, bad, otherwise?
 

·
Administrator
Joined
·
6,157 Posts
Bad idea

The pre-charge system operates by charging the capacitors through an extra resister (I use a kettle element)

So when you close the first contactor - no current flows
Then you close the pre-charge contactor
Then you close the second main contactor

Using two pre-charge systems simply can't work
 

·
Registered
Joined
·
508 Posts
My main concern with using the BMS to open a contactor is that it might happen under load. You don't want to have the situation where a momentary dip below some LVC causes it to open. This might be in the middle of some acceleration event, example, passing a car. It could also damage the contacts which are impossible to inspect with an enclosed contactor. I have an "okay" green light wired to my Orion and I find sometimes it goes out for strange reasons which have nothing to do with protecting the pack. With a light you can always slow down and check things out in a secure setting.
 

·
Registered
Joined
·
16 Posts
Discussion Starter #4
OK, So I have abandoned the idea of two main contactors. The EMUS BMS has a circuit to cut power to protect the batteries. They recommend connecting it to the main power contactor. I don't like that idea either. HPEV recommends connecting it to the throttle switch to cut battery output.
I am not using a clutch switch and thought that might be a good circuit to control batteries.


Any suggestions on using the EMUS BMS to control battery load?
 

·
Administrator
Joined
·
6,157 Posts
BAD IDEA
You should use two main contactors - it's a legal requirement here and is should be elsewhere

Only one of them should be part of the "pre-charge" system

You do NOT want to be opening either of those contactors everytime you take your foot off the throttle - bad idea and will lead to the contactor failing SHUT

I would suggest that the BMS warning is more like an Oil Pressure light
It should NOT "do anything" so much as be a BIG warning that something is wrong

Not sure if you are using AC and can use re-gen

I'm using a series DC motor so Re-gen is not an option

This does mean that I can use a very simple circuit to shut the throttle down to zero whenever I touch the brakes
 

·
Registered
Joined
·
508 Posts
You can get away with a single contactor with an A.C. motor but I would always use two contactors with a D.C. setup. DC controllers typically fail "on" and you need all the help you can get to open the circuit should this happen. First contactor turns on with keyswitch, second (typically) is activated by the controller. If not, then use a separate switch to "arm" the system.
 

·
Registered
Joined
·
209 Posts
Do I understand your question correctly that you want your Emus BMS to intervene by not allowing a throttle signal to get to the controller rather than opening a main contactor?

Perhaps it is possible, but would not do it myself. What if someone is driving, the BMS intervenes and to the controller it looks like the throttle is not pressed at all and the current drops. Problem no longer triggering that intervention (if for example the reason was low voltage error due to voltage sag).
In the meantime, the driver is confused due to no throttle response and plays around and floors the pedal. An in that moment the BMS resumes the throttle signal to the VCU..... bad things can happen.
And at the same time: if the error is caused by low SOC or high temperature, the controller current drops to zero but how about power used by the dc/dc and heater?
Personally I prefer a BMS to be in control of a pack being “online” and thus have the ability to open contactors during errors.
A safety plus is that you will need to restart and go through precharge again (assuming the bms goes out of drive mode and into ready mode after having opened a contactor.
 

·
Registered
Joined
·
158 Posts
Hi i have a similar setup with emus bms and hpevs ac motors and curtis controller. The emus guide suggested circuits does show controlling the main contactors from the bms. The HPEVS circuits have the main contactors controlled from the curtis and thus it controls the precharge relay etc which makes sense.

I am considering having further contactors within each battery box which only come on when u turn the ignition switch which would then energise the curtis controllers at the same time (as the 12v supply to the curtis is also on the ignition circuit as is the bms). This would mean that normally when the ignition is off no HV cables are live outside of the battery boxes. I did wonder about allowing the bms to control these contactors might be a good idea but actually the risk is higher i think from the bms suddenly cutting power when a voltage sags (this i guess could be likely at full acceleration when current is at full draw and this would surely cut the contactor life) and im not sure any of the BMS alarm states (low voltage high temp etc ) really justify an instant contactor cutoff and just a big red warning light on the dash would be enough for you to slow down and stop as soon as safe and investigate. I do have 2 big emergency stop switches on the dash that either cut the throttle supply for if the throttle cable snaps or sticks on as i have a direct chain drive and no clutch) and one that cuts 12v power to the curtis controller which hpevs reckon was ok to be used in a true emergency and would cut power to the contactors and stop everything. I did consider a third cutoff swith which cut power to my battery pack contactors but left the ignition on these might be helpful if the insulation montor detected a leak from battery pack to chasssis. I also have an internia switch which also cuts power to the curtis controller if there is a crash.

Any views on this would be gratefully received
 

·
Registered
Joined
·
508 Posts
It looks to me like your setup is fine. The throttle "cutoff" switch will probably never be used - but you never know. Two contactors is never a bad idea: first wired through ignition switch and second controlled by the controller. If you were racing, a switch to interrupt power to the contactor coils would be required.

Using the third contactor would be a personal choice I guess, but you could obtain the same functionality with two, depending how you wired them; ex. key switch to leave basic functionality "active", toggle switch to activate first contactor, then momentary push-button switch to "start" the system up.
 
1 - 9 of 9 Posts
Top