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BaldBruce
22 March 2011, 1653
Thought I would start a new thread on the simple BMS concept. I need to apologize for two things first. I have been very slow at sharing all this only because of the insane hours I have been pulling at work in the recent months and the trips to China. Hopefully now that we have launched some of these new fangled LED lighting products, my shedule can get back to normal.... well, normal is such an overused term. twitch twitch..

Second on my apology list is I forgot who came up with the KISS my BMS moniker. Whomever that was,stand up and take a bow.

Here is the schematic for interfacing three Cell Log 8 products to your charger and throttle.

929

BaldBruce
22 March 2011, 1700
http://www.elmoto.net/attachment.php?attachmentid=237&d=1283057357

Here is what the prototype looked like. You will note that only one input is wired so far in that particular picture.

This system provides very low cost HVC, LVC and Delta V protection.

BaldBruce
22 March 2011, 1719
Here is the back of the board showing the red LED operating which indicates an alarm condition has occurred. Size is 1 inch by 2.8 inches.

930

Function is to take three Cell Log 8 products and combine their alarm functions in a safe isolated manner.

Charger operatiom is controlled by routing AC supply from charger through the relay. That way if any logger detects an overvolatge cel, it will open and latch off the charger circuit.

LVC and cell mismatch protection are provided by the same relay but an independant pole. This connection can be used in many ways to shut down or throttlle back the controller. I choose to use it to switch in a resistor to limit the throttle input to half it's normal range when a low voltage or large delta votage situation occurs.

BaldBruce
22 March 2011, 1722
Here is the schematic on my bike's main power connections showing how "Kiss my BMS" could be used.
931

DaveAK
22 March 2011, 1727
Do you hand solder your SMD parts? That's something I haven't attempted yet.

Coninsan
22 March 2011, 1727
Great stuff Bruce!

One thing I am noticing though, you AC in and out, their hopefully not supposed to pull the full AC input to the charger right?
Wouldn't it be safer to run this via a solid state relay like on the Mini-BMS?

BaldBruce
22 March 2011, 1732
Do you hand solder your SMD parts? That's something I haven't attempted yet.

Sure, just need to use the right size solder iron and solder. Or buy some paste and a reflow system if you have a few hundred spare bucks laying around.:eek:

Really not that hard for these sized components. I purposelly used everyting 0805 or bigger to make it easy to prototype.

BaldBruce
22 March 2011, 1735
Great stuff Bruce!

One thing I am noticing though, you AC in and out, their hopefully not supposed to pull the full AC input to the charger right?
Wouldn't it be safer to run this via a solid state relay like on the Mini-BMS?

My particular charger is a small on board one that pulls less than 2 amps and so can be handled directly by this small relay. You would want this small one to drive a big external relay if you were using a monster off board charger. Safer??? not sure I follow.

Coninsan
22 March 2011, 1741
My particular charger is a small on board one that pulls less than 2 amps and so can be handled directly by this small relay. You would want this small one to drive a big external relay if you were using a monster off board charger. Safer??? not sure I follow.

Safety meant as a lower risc of burning you BMS with a oversized Charger. But I see that you've already got that figured :)

Nuts & Volts
22 March 2011, 1838
Thanks Bruce! I remember see this before now.

Ok so I want to try to understand this, I am pretty bad at reading schematics. The cell log alarm will close the optocoupler, which in turn closes Q1 and K2. Q1 basically turns on an LED indicator?? And K2 is a double pole switch which opens AC mains so your charger has no pwr and also opens throttle so you stop drawing current?? Q2 is turned on when the AC Mains is switched over, but i dont know what its purpose is??

I do understand that a mosfet closes when a voltage is applied across it, but im bad at follow current paths.

Am I close? Sorry I suck :)

BaldBruce
22 March 2011, 1902
You basically have it. I'll cover it for you in gorry detail.

An alarm input from the Logger turns on the input LED inside the optocoupler. This causes the output of the opto to go from open to conducting. (The resistor in series with each of the inputs limits the current through the opto led so you don't harm it.)

Now Q1 is a P type FET. This means it is off when the gate has 12 volts on it. (normal operation.) When the optocoupler output conducts it drops the gate of Q2 from 12 volts to effectively zero volts and thus turns it on. R1 limits the current when we pull the opto output low.

When Q1 conducts it turns on the LED and the relay energizes. (resistor R4 in series with the LED limits current, while diode D1 protects the circuit from the reverse spike when the relay de-energizes.) The relay of couse can be connected to many outputs, but I chose the AC of the charger and a cutback resistor across the throttle.

The circuit in the lower right does nothing until the alarm trips and if the AC is plugged in. If these two conditions are present Q2 conducts to latch the relay on while the rest of the circuit derives the gate drive necessary to keep this N type FET conducting until you unplug it or reset it by applying a ground to the reset input. This is to prevent cycling from your charger. Once any cell hits HVC, you are finished until you reset.

Clear as mud???:cool:

ZoomSmith
22 March 2011, 2235
Whomever that was,stand up and take a bow
Done.

-Zoom

Nuts & Volts
22 March 2011, 2315
You basically have it. I'll cover it for you in gorry detail.

An alarm input from the Logger turns on the input LED inside the optocoupler. This causes the output of the opto to go from open to conducting. (The resistor in series with each of the inputs limits the current through the opto led so you don't harm it.)

Now Q1 is a P type FET. This means it is off when the gate has 12 volts on it. (normal operation.) When the optocoupler output conducts it drops the gate of Q2 from 12 volts to effectively zero volts and thus turns it on. R1 limits the current when we pull the opto output low.

When Q1 conducts it turns on the LED and the relay energizes. (resistor R4 in series with the LED limits current, while diode D1 protects the circuit from the reverse spike when the relay de-energizes.) The relay of couse can be connected to many outputs, but I chose the AC of the charger and a cutback resistor across the throttle.

The circuit in the lower right does nothing until the alarm trips and if the AC is plugged in. If these two conditions are present Q2 conducts to latch the relay on while the rest of the circuit derives the gate drive necessary to keep this N type FET conducting until you unplug it or reset it by applying a ground to the reset input. This is to prevent cycling from your charger. Once any cell hits HVC, you are finished until you reset.

Clear as mud???:cool:

That definitely helps, thanks again! So K2 is a double pole relay then, one pole on the throttle and one on the charger? Or did you just connect those two in parallel?

I think for mine I would have the relay drive a contactor or just directly drive a contactor on the charging circuit. I would use a contactor due to my HV needs. You could also send a signal to the charger if your charger has a cutoff circuit

frodus
23 March 2011, 0820
man this would be great if you made it for 48 cells, those car guys would love it. They're always bitching about BMS's and how you shouldn't use one, top balance, bottom balance, blah blah. Thing is, I don't care WHAT you do, but monitoring and LVC/HVC is important. Those cell logs are great!

ZoomSmith
23 March 2011, 1259
An alarm input from the Logger turns on the input LED inside the optocoupler......
.............you are finished until you reset.

Oops sorry, I went into an EE induced catatonic state.

Any chance you translate this Bruce?

BaldBruce
23 March 2011, 1923
man this would be great if you made it for 48 cells, those car guys would love it. They're always bitching about BMS's and how you shouldn't use one, top balance, bottom balance, blah blah. Thing is, I don't care WHAT you do, but monitoring and LVC/HVC is important. Those cell logs are great!

That would be easy. It is simply 3 more optocouplers. It would then cover all ranges we might need for any El Moto voltage we might normally see. Not to many bikes over 144V. I used a very small relay for mine, but I would envision a bit bigger one for more general use. Amperage of 10 good enough for most users? Should I build you a prototype to test?

BaldBruce
23 March 2011, 1927
Oops sorry, I went into an EE induced catatonic state.

Any chance you translate this Bruce?

Ya plug it in and it works to stop wise guys from self destructing their batteries.........

BaldBruce
24 March 2011, 0018
144V version schematic
Layout is done too but I won't bother you with the details. Put in two relays so I could switch 15Amps though. Still pretty small board.
939

Coninsan
24 March 2011, 0338
Beautifull Bruce :)
I see the ground also listed as AC neutral, what does this mean for wiring the AC from the charger through the board? And more crucially, will it hold 220 volt AC?

SplinterOz
24 March 2011, 0354
Bruce... love your work... will be building one of these very soon.

frodus
24 March 2011, 0807
Bruce, Thanks a ton for doing that. I know more and more people are getting those celllog's and using them in their vehicles. It's a great cheap simple solution for people that want protection but don't really want a full BMS.

BaldBruce
24 March 2011, 0936
Beautifull Bruce :) <BR>I see the ground also listed as AC neutral, what does this mean for wiring the AC from the charger through the board? And more crucially, will it hold 220 volt AC?<BR><BR>This is a 120V product due to the choice of components for the relay latching circuit. Other than that it is a 12V circuit. So you could use it on 240VAC by tweaking the holding circuit values or removing the resistor to make that part inoperative. The neutral connection is necessary only from a reference voltage standpoint and is not passed through to the charger or anything else. It just enables the latching circuit by having a return path for the tiny amount of current the latch circuit needs. Main neutral line would bypass this PCB and be wired straight to the charger.

BaldBruce
24 March 2011, 1747
Prototype PCB ordered. Due to ship April 8. Part ordering for the couple component pieces I don't have in stock is next. Schedule is to have 2 protos built and tested in the next three weeks. (I'm too cheap to pay for really fast PCBs!!!!) Recomend we prove out this version before making any quantity of these boards.

DaveAK
24 March 2011, 1811
Who do you use for your PCBs? What about someone who will solder on SMD parts for someone who's not up to the challenge just yet. :)

BaldBruce
24 March 2011, 1827
Sunstone PCB. Some assembly required.:eek:

Seriously though - I will of course help any and all Elmoto Members if they want to go down this path.

I'll solder one up for a nominal fee to cover my costs - even for you Dave......

BOM attached :945

DaveAK
24 March 2011, 1850
I'm working up my BMS layout right now. I got my LTC4803 chips today. 44 pin SSOP package. Scary stuff!

BaldBruce
24 March 2011, 1924
Did you mean the LTC 6803?????

If you want just one or two soldered in place, I would be glad to do it for you. I work with packages far worse than this one at work every day. BGA packages are the real monstors. We have to x-ray the damn things to see the tiny little connections hidden underneath.....

Nuts & Volts
24 March 2011, 1951
Sweet, Bruce I will be interested in these in the future. I would prolly pay you to solder them and the beer necessary, but I may want to try a board or two myself to get the practice.

Any concerns with going higher voltage on these. Say a battery pack of 400V with 13-17 cell loggers? I realize I would have multiple PCBs.

DaveAK
24 March 2011, 2012
Did you mean the LTC 6803?????

If you want just one or two soldered in place, I would be glad to do it for you. I work with packages far worse than this one at work every day. BGA packages are the real monstors. We have to x-ray the damn things to see the tiny little connections hidden underneath.....
Yup, the 6803. Just a typo. Right now I'm laying out the schematic. Apart from the LTC6803 I can go through hole for everything else, but I'm going all out on SMD right now. :) Haven't made a final decision, but if it's just going to be a couple of chips I might take you up on your offer.

BaldBruce
25 March 2011, 1748
Sweet, Bruce I will be interested in these in the future. I would prolly pay you to solder them and the beer necessary, but I may want to try a board or two myself to get the practice.

Any concerns with going higher voltage on these. Say a battery pack of 400V with 13-17 cell loggers? I realize I would have multiple PCBs.

Nope. The isolation of the opto couplers is way over 2500V. Just use one small pcb per 72v or the larger pcb per 144V. Just wire the output relays in parralel for the LVC circuit and wire the HVC in series to interrupt the charger. Your 400V example would need three of the 144V PCBs.

BaldBruce
25 March 2011, 1816
The price for a particular pcb depends on many factors, but the two biggest are time and quantity ordered. I'll be putting an order together for some of the 144V version pcbs on lets say May 1 after I have proven I have no bugsin my layout. So who wants one? or 3?

Example price for the 2 protoypes I ordered with a 10 day lead time was 55 bucks with shipping included. $27.50 each

If I had gotton that with a 2 day delivery the price jumped to 750 bucks!
If I had ordered 10 PCBs in a three week lead time the cost was 120 bucks. $12 each

The more people we can put orders in together the lower the price per board.
I'll look up the Newark prices and let you know what the pieces-parts cost also.

SplinterOz
25 March 2011, 1854
I would only want the 72 volt one... maybe two of them.

Nuts & Volts
25 March 2011, 1911
I would only want the 72 volt one... maybe two of them.

Well you could still get the 144 board and only populate it with what you need. The difference in cost of the board could be as little as $5.

Anyways I am in for 3 boards, is there a way to maybe have the board run a contactor on HVC?? instead off having to run the AC through the board?

Thanks Bruce

BaldBruce
25 March 2011, 2109
Of cource you can run an external contactor if that is your need. Just run whatever voltage you need to operate the external contactor through the relay contact. The relays are rated for 250VAC or 30VDC maximums at 16 amps so you can easily drive any normal contactor.

BaldBruce
25 March 2011, 2116
Costed BMS attached. Looks like all the parts will cost just under 10 bucks. You might shave a few pennies here or there with other selections, but be carefull substituting parts unless you completely understand the ramifications.
Figure another 10 bucks maximum for the pcb and you can have a KISS my BMS for less than 20 bucks!

947

Nuts & Volts
25 March 2011, 2147
Awesome! Very well designed indeed. It gives me some flexibility with what I externally switch on and off

This is way better, safer and more organized than anything I would have wired together by hand :) I'm excited

SplinterOz
26 March 2011, 0152
ok count me in for 4... that will cover me, Mark, Paul and one spare.... :)

Nuts & Volts
24 May 2011, 1058
Any updates Bruce? I am actually interested in using some of these in late June. I dont mind being somewhat of a beta tester if necessary.
Thanks

ZoomSmith
24 May 2011, 1216
Bruce, if you are still counting, count me in for a couple.