Zero-Draw, Solid State Contactor w/Precharge (Arduino)

[rf]

One of the equipment manufacturers warned against using pre-charge resistors with their controllers, saying they would cause damage. They said, if you must, something like 1.8 ohms was as high as you should go.

I wonder exactly what the issue is there?

The constant rate ramp precharge thing I did seems to solve a lot of issues and is super easy to implement.

Processor starting before power is stable, crashing and leaving wrong things on?

 

[fechter]

Processor starting before power is stable, crashing and leaving wrong things on?

Yeah, probably something like that. If the controller is getting powered through a resistor about the time it does it's startup beep routine, it could cause the voltage to drop out and malfunction.

 

[jonescg]

On almost all large scale EV's they just permanently strap a precharge resistor across the relay. I am beginning to think of our bikes as high power enough to warrant that... tho... if a controller is left on enough current can creep through to drain our tiny packs so much faster.
...
So - if you string a 5K resistor across your contactor terminals you will be good for a full month of leaving it on (minus contactor power). Most EV's do something more like 750 ohms etc.

Chiggy CHeck it - you should do that.

-methods

If not for the TTXGP rules which state the controller needs to be discharged in seconds once the bike is turned off, I would do exactly this. The caps are unlikely to be all that leaky, even with say a 500 ohm resistor. That said, I have three additional contactors to break my pack up, so I'd need precharge resistors on al of them too... Yeah I think my HV relay / delay system will work OK.

 

[liveforphysics]

I've never seen an large EV that had a permanent pre-charge across the contactor. Everything big Ive seen has controller integrated precharge or external pre-charge hardware like most hybrid cars feature.

 

[methods]

I've never seen an large EV that had a permanent pre-charge across the contactor. Everything big Ive seen has controller integrated precharge or external pre-charge hardware like most hybrid cars feature.

Then you have not seen like 99.9% of EV's.... i.e golf carts and buggies. These guys have been doing this since the 50's - it is not new. The Sevcon and the new Owl Trax that have built in precharge are totally new. Yes - they are bad ass - but only 0.1% of people actually own a Sevcon so the majority solution is still a precharge across the contactor.

-methods

EDIT: Big is a relative term. RC is what I would call small - like a skate board or a 1kw bike. Mid size would be golf carts, buggies, and small ev's like a bug. Then - you did say "big" - which would be a full sized EV car or a high power bike... So I guess I would agree with you that "BIG" Ev's dont use a precharge like that - but BIG ev's are also high budget and not really what your average EV guy is working with. (for now - till they start hitting the junk yard where we can pick-n-pull)

EDIT 2: The BIG EV's dont avoid a precharge across the contactor because it does not work... they do it because LAW forces them to be able to discharge the system to be "safe". I know you are a big advocate of THE LAW lol...

 

[rf]

One of the equipment manufacturers warned against using pre-charge resistors with their controllers, saying they would cause damage. They said, if you must, something like 1.8 ohms was as high as you should go.

I wonder exactly what the issue is there?

The constant rate ramp precharge thing I did seems to solve a lot of issues and is super easy to implement.

Fechter: where can we find a refresher on your constant rate ramp precharge? (And why do I always put the t in the wrong place when I type your name?)

 

[circuit]

I've never seen an large EV that had a permanent pre-charge across the contactor. Everything big Ive seen has controller integrated precharge or external pre-charge hardware like most hybrid cars feature.

Then you have not seen like 99.9% of EV's.... i.e golf carts and buggies. These guys have been doing this since the 50's - it is not new. The Sevcon and the new Owl Trax that have built in precharge are totally new. Yes - they are bad ass - but only 0.1% of people actually own a Sevcon so the majority solution is still a precharge across the contactor.

-methods

EDIT: Big is a relative term. RC is what I would call small - like a skate board or a 1kw bike. Mid size would be golf carts, buggies, and small ev's like a bug. Then - you did say "big" - which would be a full sized EV car or a high power bike... So I guess I would agree with you that "BIG" Ev's dont use a precharge like that - but BIG ev's are also high budget and not really what your average EV guy is working with. (for now - till they start hitting the junk yard where we can pick-n-pull)

EDIT 2: The BIG EV's dont avoid a precharge across the contactor because it does not work... they do it because LAW forces them to be able to discharge the system to be "safe". I know you are a big advocate of THE LAW lol...

Depends on what you call "all EVs". Golf carts? Probably they are a "<60V systems", where it is not necessary to have no voltage or leakage detection. DIY EVs? Those are built to no standard. Normal EVs, such as Tesla, use numerous contactors, not only on positive battery terminal, but also negative and sometimes in a few in the middle of pack to split it to "<60V" packs. Proper precharge circuitry, leakage detection, etc. Dealing with high energy packs is no joke, you need to take special safety measures.

 

[fechter]

Fechter: where can we find a refresher on your constant rate ramp precharge? (And why do I always put the t in the wrong place when I type your name?)

"Methods" version is on page 9 of this thread.
Long-winded development thread here: http://endless-sphere.com/forums/viewtopic.php?f=3&t=40142
Actual hardware: http://endless-sphere.com/forums/viewtopic.php?f=31&t=49026

 

[liveforphysics]

I've never seen an large EV that had a permanent pre-charge across the contactor. Everything big Ive seen has controller integrated precharge or external pre-charge hardware like most hybrid cars feature.

Then you have not seen like 99.9% of EV's.... i.e golf carts and buggies. These guys have been doing this since the 50's - it is not new. The Sevcon and the new Owl Trax that have built in precharge are totally new. Yes - they are bad ass - but only 0.1% of people actually own a Sevcon so the majority solution is still a precharge across the contactor.

-methods

EDIT: Big is a relative term. RC is what I would call small - like a skate board or a 1kw bike. Mid size would be golf carts, buggies, and small ev's like a bug. Then - you did say "big" - which would be a full sized EV car or a high power bike... So I guess I would agree with you that "BIG" Ev's dont use a precharge like that - but BIG ev's are also high budget and not really what your average EV guy is working with. (for now - till they start hitting the junk yard where we can pick-n-pull)

EDIT 2: The BIG EV's dont avoid a precharge across the contactor because it does not work... they do it because LAW forces them to be able to discharge the system to be "safe". I know you are a big advocate of THE LAW lol...

HEVs is a category with parameters.
Golf karts do not fall into it.

The reason it's not done in HEVs is the delay would be unacceptable between turning the key on and getting to an acceptable voltage drop that wont damage the contactor prematurely. You can shave a lot of time off the top-end of the precharge process with active control.

 

[methods]

Your logic does not follow.

There would be no delay because the resistor spans the contactor at ALL TIMES therefore the controller input caps are never drained therefor they never have to be refilled (other than the very first time - which would happen at the factory or after service)

It is only the regulations (like at the TTXGP) that say the controller must be completely discharged.

Tell me why you would not just hang a PreCharge resistor across your terminals and never drain down the internal caps in the controller. Not a postfacto argument justifying why it is done - but a real arguement for why it SHOULD be done.

Leaky caps? I dont buy that argument. My current meter says there is little to no leakage.
Safety? I dont buy that either for a personal EV.

-methods

HEVs is a category with parameters.
Golf karts do not fall into it.

The reason it's not done in HEVs is the delay would be unacceptable between turning the key on and getting to an acceptable voltage drop that wont damage the contactor prematurely. You can shave a lot of time off the top-end of the precharge process with active control.

 

[Arlo1]

Your logic does not follow.

There would be no delay because the resistor spans the contactor at ALL TIMES therefore the controller input caps are never drained therefor they never have to be refilled (other than the very first time - which would happen at the factory or after service)

It is only the regulations (like at the TTXGP) that say the controller must be completely discharged.

Tell me why you would not just hang a PreCharge resistor across your terminals and never drain down the internal caps in the controller. Not a postfacto argument justifying why it is done - but a real arguement for why it SHOULD be done.

Leaky caps? I dont buy that argument. My current meter says there is little to no leakage.
Safety? I dont buy that either for a personal EV.

-methods

HEVs is a category with parameters.
Golf karts do not fall into it.

The reason it's not done in HEVs is the delay would be unacceptable between turning the key on and getting to an acceptable voltage drop that wont damage the contactor prematurely. You can shave a lot of time off the top-end of the precharge process with active control.

Don't most china, maybe most all cotnrollers have bleed resistors inside them from + to -? I know I saw this on at least one of my many china controllers and wondered WTF is it there for? But Zombies just showed us he is adding them as well and with all my experimenting its actualy a good thing. I would chose not to have precharge on the controller all the time... If it was maybe on a switch with a fuse. I blow a lot of shit up and having a fuse is good to stop from burning up a lower resistance precharge... I higher precharge will never bring the caps up all the way with things I have added to my controller.

 

[jonescg]

Arlo - All Kelly controllers show the wiring diagram with a 20 W resistor permanently across the contactor.

I think precharge circuits are a total pain in the arse. I would really prefer not to have them, but where a rule states you must discharge the caps in the controller you need a separate precharge-discharge circuit. For any EV up to about 450 VDC, I reckon that a big, 20 W resistor permanently across the main contactor is a winner. Then the only reason you would need to use a precharge again is after breaking the pack up into safer voltage units, but even then the caps are probably still well charged.

Precharge circuits, especially ones where there is an additional switch or HV relay / Solid state etc, are just another point of failure, and it's an epic failure when it does happen. frock, even Zeros can weld contactors! The hoverpod I've been working on needed a discharge circuit because while we're in prototype stage there's some painful voltages around. So we came up with a precharge-discharge through a relay and delayed contactor on. Which worked great until someone turned it off too soon after turning it on. Boom, relay blew up, welded shut and threw sparks several meters across the shop floor.

So yeah, don't go fooling around with precharge-discharge if you don't have to.

 

[Arlo1]

What IM trying to say is... With my e-bmx for instance. I used to leave my power wires attached to the bike... I bricked my last battery from that. What happened is I didn't use it for over 1 month and the batteries were at the safe 3.8 per cell but.. That's not much energy in the pack so it slowly discharged it self to nothing.
I want a switch that turns off the contactor and cuts all power from the battery to the controller so it can sit as long as I am gone away from it with 0 draw!
My DIY controller uses ~35 watts to run the CA and the fans, now of course I can have them on a switch or something but lets be honest its a diy controller what if something I built is not perfect and fails while I'm away.... So for these 2 reasons I want the caps discharged as well. What I'm planning is a Pre-Charge with a contactor like fetcher drew up for me and a couple Hi OHM resistors from + to - in the controller! Its not that hard to do and well worth it to me.

 

[bigmoose]

I keep thinking through our "topology" in a "systems approach." What we currently have (component wise), is sure not optimum or well thought out.

The precharge/contactor "module" should provide bidirectional isolation and precharge. To do that easily, there needs to be no parasitic draw in the controller and subsequent hotel loads. In otherwords the controller and everything downstream needs to be "OFF" during the precharge.

We can accomplish this with a system level switch that has two NO conacts. The first one closes to precharge (like an ARM switch) and then you count to 5 and turn it to RUN. Now that would work, but it puts the operator in the loop to count right, not forget, and not short cycle things.

A better approach is a precharge/contactor (PC) "module" that takes the input from the "ignition switch", a simple NO (Normally Open) contact that you close to "turn things on" This switch should switch battery voltage to the precharge/contactor module. When the PC module has sensed that the caps are charged, it closes the contactor (whether solid state or contactor) and then sends a permissive signal to the controller to turn on about 500 mSec after the contactor close command. Like an opto isolated NPN transistor with both leads going back to the controller.

The circuitry should be "smart" and if a contactor is used it should contain an economizer to minimize coil current and hence current draw from the battery.

Till our discussions on this thread, I never thought about it including a dissipative function to drain the controller's caps, but that could "easily" :? (except for the heat) be added to the downstream side of the contactor.

Also, apologies to methods for posting this in his thread. Arlo got me thinking again with his post above, and thought I would share my thoughts. If methods thinks it inappropriate, I'll move it to another thread. I always thought methods provides the glue to make the available pieces we have access to work better, I guess I keep thinking about the "ultimate system" that no one has yet built.

edit: PS Does anyone know the legal requirement for the nominal time to discharge the controller caps?

 

[fechter]

I've ruined some batteries by having the controller always connected also. The only drain was cap leakage, but that was enough over a few months. Precharging through a resistor pretty much requires there is no other load than the caps, otherwise you'll never reach pack voltage by the time the main contacts close. While this can be done easily enough in most setups, it would be better if the precharge circuit could handle some drain, like a dc-dc converter or the controller logic power. This can simplify wiring.

I've also heard more than one report of a voltage spike making through the charger and blowing the controller FETs resulting in a sudden full power to the motor (brushed system). This can happen if you live where they have lightning. Best to completely disconnect the controller when not riding.

I tried designing something like bigmoose is talking about where you monitor the cap voltage and kick in the main switch when it charges up enough. It got really complex and I went for another approach. It could be done with a microcontroller and not be too bad.

A lot of systems just use a big contactor and slam the caps with full voltage when the contacts close. OK for a small system, but will weld the contacts shut if you have a larger system. Even if the contacts don't stick, it has to be rough on them.

 

[bigmoose]

fechter I agree with you. Precharge/contactor module would be smart with a micro. It would precharge as a constant current source to the controller. Again, not simple and "cheap" and not as robust as analog...

 

[liveforphysics]

I sometimes go months without touching various ebike setups. This is why if I'm going to go through the trouble of doing a disconnect system, I want it to not fail a pack like my tiny 5Ah roadbike pack if I park it at medium/low SOC.

IMHO, it either does the complete job and poses no risk to the pack or it's not something I would bother with changing from the two little crappy RC plugs I have now, one with a resistor. Gives me precharge and complete isolation already, it's just less convenient than a simple switch on the handle bar that does it for me without bending down fumbling with plugs.

 

[fechter]

Luke, if you just used a big FET switch and slammed it on super fast so it doesn't have time to heat up, do you think it would survive? I know they blow up if they're turned on at the wrong speed for sure (tested repeatedly). This would be the equivalent of using a contactor with no precharge. You'd get some seriously high peak currents, but the parts might survive it.

What happens to the caps when you do this? Seems like 1,000A could possibly damage something, but maybe the ESR is enough to limit it to a safe level.

 

[John in CR]

What's the safety issue that draining the caps when off solves?

 

[methods]

Big Moose - you guys are of course free to speak of anything you like in my threads - I always say this. Everyone is welcome except belligerent haters.

Hey guys - Keep up the discussion and find the best solution!
I am checking out

I am at Starbucks right now uploading the boot loader to this Arduino SSR, then I will write up some test code, then I will burn it in for a week, then I will finish off this short production run of 10pcs to satisfy those who I have promised deliverables to, then I will make another short run of 20 to 50 for myself (I want about 10) and for folks who need HVC control in the future.

That will be the last of my contribution for a while. I am moving on to take a straight job for 3 to 5 to 10 years to refill my war chest. I am sick and tired of working in a bleeding hot greenhouse on dirt floors, broke, with an unhappy wife, mountains of deferred maintenance, no health care, looking like a hillbilly slob, etc.

I want to work at Google. I think that will maximize my impact.

So - I will be out for a year while I re-establish my bad-ass-ness and make a new name for myself... then I will be back enforce with a big budget and a big ego and we can get this shit rolling again.

-methods

 

[methods]

Sweet... I got the AVRISP MKii hooked up and green light. Used an Adafruit mini-programming port that required some serious ghetto rigging to get working. Got the power hooked up. Regulator output is 5.003V on my 87V.

Ready to strap the boot loader - off to look up all the mini-versions of Arduino that folks claim work.

Goal for today?

1) Get a boot loader on it
2) Get a blinking LED (in this case - a blinking gate level mosfet)
3) Load up a testing profile
4) Go back to my dusty, sweaty, hot, shitty shop and hook this up between a 100AH 100V pack and some sort of representative load - or over-representative load.

Then - I am going to go get the three boogie boards I have... all of which were made for kids... and duct tape them together to make them buoyant enough to keep me infront of the white water instead of drowning in it! I have one with a hard bottom and two from the 80's that are basically just blocks of foam. Starting with 2 - I am heading out to the big waves at the lighthouse and we are going to see if I can eat rocks. I really need to get some GoPro video of the local bad-asses... they wait next to a cliff for big waves to come in and catch them just before getting smashed up against the rocks. Dudes are LOCO... I catch the white wash from those waves and that is a blast. Kind of tired of surfing - body boarding can be done with much more abandon because there is no fear of hurting anyone else or the board. I can let loose.

-methods

 

[bigmoose]

...That will be the last of my contribution for a while. I am moving on to take a straight job for 3 to 5 to 10 years to refill my war chest....I want to work at Google. I think that will maximize my impact....So - I will be out for a year ...
-methods

Nooooooooooooooooooooooo!!

I think Google became an extension of the N S A during the past years... Tesla seems like your kind of company or SpaceX might even be better!

 

[methods]

I have had a change of mind.
I will work where I can. Do what I must
I need to maximize my income for the next stage of the revolution.

I learned what I needed to learn here - I now understand the role that cash plays in this game. I have to leave some of my ideals behind - at least for a while - so that I can develop the power (in the form of cash/tools/workspace) to make my dreams come true.

-methods

 

[bigmoose]

You speak truth methods, cold starts take capital and lots of it. I really believe the rumor that most businesses operate at a net loss for 3 years.

I cannot justify my "dabbling" with this stuff with any business case I can generate. My friends who have started businesses from scratch have me in awe. I can optimize an existing business and tune it's products; but I am starting to believe that I do not have the required insight, temperament and skills to start something (and make it profitable) from scratch. ... my Dad couldn't do it either, but his Dad could and did in the 1920's. Grandpa owned and ran a general store in the coal patches of Pennsylvania before the Great Depression.

 

[methods]

I am excited

Nothing is more rewarding that reinventing myself - again.

-methods