Multi-Cell Slave-Version 2

Threads relating to the BMS system begun by Peter Perkins

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Kicad schematic

Postby GregsGarage » Sat Feb 25, 2012 4:42 pm

I've redrawn the schematic using Kicad. It's been a while since I last tried it, so far so good. :D Components have been moved on the schematic just to try and make it clearer, they have no reflection on how I am thinking of positioning them on the actual pcb. The component reference system I was using had to be changed a bit. So capacitor C1 on the first cell was referenced as C1a now becomes C101, C1d is now C104, etc. I had to do this because Kicad uses the letter suffix for multi part components such as op-amps that may have 4 op-amps on one chip.
Attachments
4Cell250212.jpeg
4 Cell Slave redrawn with Kicad 25-02-2012
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Re: Multi-Cell Slave-Version 2

Postby retepsnikrep » Sat Feb 25, 2012 10:09 pm

Looks ok but we said a lower value resistor for the transistor driver IIRC

We also said 10uf for the bigger cap
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Re: Multi-Cell Slave-Version 2

Postby GregsGarage » Sun Feb 26, 2012 1:21 pm

R3xx (driver resistor) at 330R gives a current of around 10ma @ 3.6 volts. A 220R would be 16ma @ 3.6 and 19ma @ 4.2 volts. I could change it to 220R if you think that would help. I will also update C2xx to 10u. I am working on the layout, it's a bit tricky making it all fit. I am thinking of stacking the ICSP headers into pairs of 2. This will allow programming from the edge of the board with 90 degree headers.
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Pictures of progress on 4 cell slave.

Postby GregsGarage » Mon Feb 27, 2012 1:25 pm

I've still got some work to do, but here are a couple of screen shots of the board in 3d view. I don't have a 3d model of the optos so they just show pads at the moment and the board is about half routed. I've paired up the ICSP headers so that you have the option of fitting straight or 90 deg pins, or nothing at all. I will add some holes in the crner for mounting, although I plan on sliding them into a case with grooves. Any comments?
Attachments
Bottom1.jpg
Bottom1.jpg (127.68 KiB) Viewed 8594 times
Top1.jpg
Top1.jpg (150.16 KiB) Viewed 8594 times
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Re: Multi-Cell Slave-Version 2

Postby retepsnikrep » Mon Feb 27, 2012 1:51 pm

Impressive models. 8)

If we are going smd I think we should have smd leds, transistors and caps as well.
In fact everything except the 3w resistor which should be the only component on other side.

But if this works then we can move to full smd for the production version ;)

Not sure how you will attach header plug to the icsp in a stack?
Regards Peter

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Re: Multi-Cell Slave-Version 2

Postby GregsGarage » Mon Feb 27, 2012 2:40 pm

I was originally aiming for just the 3 watt as through hole. The transistors changed to through hole actually to save space. Using a smd transistor means you then need a via to get the signal to the opposite side of the board and was taking up more space. Same with the leds. The through hole cap is C2xx, only required if we decide to use pwm, so it is optional. C1xx is smd and again the through hole eliminates some vias.

Not sure how you will attach header plug to the icsp in a stack?

One of these cut in half. http://www.rapidonline.com/Cables-Connectors/10-10-Way-Right-Angle-Header-22-0815
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Re: Multi-Cell Slave-Version 2

Postby GregsGarage » Wed Mar 14, 2012 10:43 am

retepsnikrep wrote:If we are going smd I think we should have smd leds, transistors and caps as well.
In fact everything except the 3w resistor which should be the only component on other side.


I'm still working on the pcb layout, unfortunately I haven't been able to spend all the time I would like on it. :( After trying several different layouts, I am going to try with everything smt except the 3w resistor and leds (but if anyone has a suggestion for a right angle led let me know).

For the transistor this looks like a smt equivalent. http://uk.farnell.com/fairchild-semiconductor/bc818-40/transistor-npn-sot-23/dp/9846662

I'll change C20x to a ceramic 0805 part and the ICSP pads may need to change to smt pads, I'll see how I get on.
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Re: Multi-Cell Slave-Version 2

Postby GregsGarage » Thu Mar 15, 2012 11:01 pm

I think I've cracked it. Here's what I've got.
Attachments
top2.jpg
View from the smt side. The 3d library has the wrong part shown for the transistor, it actually only has 3 legs, not the 6 as shown. Still don't have a model for the optos.
top2.jpg (40.69 KiB) Viewed 8559 times
bottow2.jpg
View from the through hole side. I had to change the ICSP headers to smt pads and have angled them.
bottow2.jpg (61.25 KiB) Viewed 8559 times
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Re: Multi-Cell Slave-Version 2

Postby retepsnikrep » Fri Mar 16, 2012 5:52 am

Greg

Looks nice but for auto assembly in china can the machines cope with parts at an angle I've only ever seen pcb's with stuff at 90 degrees or aligned vertically or horizontally?

Also having the pic on underside oposite resistor might cause it to drift as it heats up :?

Peter
Regards Peter

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One HCH1 Civic Hybrid running 60ah A123 Lithium pack.

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Re: Multi-Cell Slave-Version 2

Postby GregsGarage » Fri Mar 16, 2012 10:21 am

retepsnikrep wrote:Looks nice but for auto assembly in china can the machines cope with parts at an angle I've only ever seen pcb's with stuff at 90 degrees or aligned vertically or horizontally?

I have thought this could be a problem, we will need to find the answer to this question. If it does increase costs then probably the easiest solution is to rotate all smd components 45 degrees, then the board can be loaded at a 45 degree angle and hey presto, all compents are 90 degrees.

Also having the pic on underside oposite resistor might cause it to drift as it heats up :?

I did try about a half dozen different approaches to get the resistor away from the pic. Now I'm not saying it can't be done, but I haven't been able to get it to work. :evil: I can post the Kicad files if someone else wants to have a go.

I think we can do a couple of things to minimize the pic heating up.

First, boards must be mounted with the resistor up or the board vertical. Heat rises so don't orient the boards with the resistor below the pic.

Second, some sort of heat insulator between resistor and board. It must be non conductive and heat resistance, maybe some bare FR4 sheets?

Third, we can do some testing and see how much drift we get with increased heat.

Fourth, don't balance on a regular basis. This last idea comes from talking to Evan Tuer a couple of weeks ago about his 106 electric which he converted from the original nicad to lithium a couple of years ago. He has come to the conclusion that he will balance the pack once a year. He has stopped doing regular balancing on his pack, finds it unnecessary. Of course your mileage will vary and maybe he has got lucky with his cells.
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