8 Battery Lead Acid Slave Board

Threads relating to the BMS system begun by Peter Perkins

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dillond666
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Re: 8 Battery Lead Acid Slave Board

Postby dillond666 » Fri Jan 28, 2011 7:15 pm

Ideas,

First I thought of joining a master board to the slave board (physically, not electrically) and routing grooves between them, simply snapping to separate. This would mean that I don't pay pcb cart the "one off tooling fee" twice, which would be cheaper.
Then I thought perhaps combining a master and slave into a single board (connected through optocoupler) would help reduce the length and number of interconnections. Two black boxes instead of three, just populate the bits you need. I was planning to optoisolate the buttons and speed sensor on the master anyway. Any thoughts? Interference nightmare?

Derek

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Re: 8 Battery Lead Acid Slave Board

Postby retepsnikrep » Fri Jan 28, 2011 7:50 pm

I think option two sounds interesting if you can fit enough slaves on a reasonable size board.
Regards Peter

Two MK1 Honda Insight's. One running 20ah A123 Lithium pack. One 8ah BetterBattery Nimh pack.
One HCH1 Civic Hybrid running 60ah A123 Lithium pack.

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dillond666
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Re: 8 Battery Lead Acid Slave Board

Postby dillond666 » Mon Jan 31, 2011 12:08 am

I've been busy doing a schematic for a combined master/8slave assembly. The main hassle is making it all compact enough when it comes to pcb layout. I now know why the world has gone surface mount! The layout for the combined board is nearly done too :wink: I'm getting more familiar with KiCad.
I got the new sensor and green leds from Farnell. I would say it is an improvement on the previous one. I have managed to fire the green light through the fibre cable and get the light detector notice it. The light detector is able to swing almost to the positive rail when the driven load is my (new spiffy) multimeter with its uber high input impedance but if you ask it to drive a 10K resistor (like the picaxe pulldown) it craps out completely. I then tried driving the base of a BC548 transistor and it is able to drive the 10K resistor to logic levels no problem 8)
I think the way to utilise this idea would be to make a smart (arse) cable assembly using the led, sensor and transistor and a bit of heatshrink goodness. This would allow the cable to be fitted (or retrofitted) to screw terminals or a molex sil pin array. The terminal on the recieving end would need positive, gnd and signal and the transmitting end needs gnd and signal.

I am using a picaxe 18m2 for the master and a tellymate for video. The 18m2 has no hardware reset though so I'm not able to do a watchdog :shock: I was going to use a dallas semi part (ds1232) for the watchdog because it looked quite good but alas it is not to be.

Derek
Last edited by dillond666 on Tue Feb 01, 2011 10:14 pm, edited 1 time in total.

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Re: 8 Battery Lead Acid Slave Board

Postby retepsnikrep » Mon Jan 31, 2011 5:54 am

We look forward to seeing it all up and running. :D

Nice the little transistor amp makes a cheapo fibre connection possible 8)

I also like the Master on the slave board idea which makes for a nice compact system for smaller numbers of cells. Avoids long interconnects and wiring errors.

Might make the basis of a neat cycle pack bms with say upto 16 cells in series. Hmm?
Regards Peter

Two MK1 Honda Insight's. One running 20ah A123 Lithium pack. One 8ah BetterBattery Nimh pack.
One HCH1 Civic Hybrid running 60ah A123 Lithium pack.

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dillond666
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Re: 8 Battery Lead Acid Slave Board

Postby dillond666 » Tue Feb 01, 2011 8:12 pm

Quick schematic of the el cheapo fibre optic receiver.
Pic input should obviously have a 10K pull down resistor. :wink:
Not tested for serial comms yet, new motherboard on order for
workshop computer :roll:
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cheapfibre.png
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dillond666
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Re: 8 Battery Lead Acid Slave Board

Postby dillond666 » Thu Feb 03, 2011 11:59 pm

Emailed the gerbers to PCB cart in China. Hope I haven't arsed anything up :shock:

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Re: 8 Battery Lead Acid Slave Board

Postby retepsnikrep » Fri Feb 04, 2011 6:41 am

:oops: I did. Good luck :shock:

How about laser diodes to shine down the fibre?

http://www.picaxeforum.co.uk/showthread.php?t=16150
Regards Peter

Two MK1 Honda Insight's. One running 20ah A123 Lithium pack. One 8ah BetterBattery Nimh pack.
One HCH1 Civic Hybrid running 60ah A123 Lithium pack.

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dillond666
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Re: 8 Battery Lead Acid Slave Board

Postby dillond666 » Mon Feb 21, 2011 10:23 pm

UPDATE:
The combined master/8 slave boards have been despatched from China :D
I've changed some of the values on the schematic to make absolutely 100% sure the picaxe adc input can't exceed 5V

I had a little play with the el cheapo fibre link but didn't get anything useful from it. Looking at things on the scope, the waveform looks more like a triangle than a square. It would perhaps be better to make use of a comparator to ensure a good solid rail to rail squarewave output. Perhaps it will be more hassle than it's worth to make it good enough for serial comms but I'll continue to tinker around with it. I've ordered a selection of electronic component goodies to play with, I'll try something with an LM393 comparator next because that would be useable for the hall effect speed sensor arrangement that I'll be home brewing :wink:

I had a little play around with some varistors and the bench power supply and can confirm that they don't seem to do much (any) clamping near their voltage so I can only suggest they be used to clamp the huge high current/voltage transient spikes, for a sharper "knee" the TVS diode or the zener seem more appropriate.
I can also confirm that it is nearly impossible to get a metal enclosure of decent size for reasonable money :( I got a couple of modem enclosures in plastic just to have a look, thinking they could be foil lined for EMI shielding but it's more likely that I will engage in some DIY metal bashing.
I was also toying with using one of the serial mp3 sound modules. This would allow the BMS to talk to you (using your pre recorded messages). Think Knight rider in the 80's. It could get tiresome pretty quickly but could also be useful and pretty cool, any thoughts?
How about laser diodes to shine down the fibre?

Perhaps, but it's the receiver that is causing the most hassle I think.

Derek

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dillond666
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Re: 8 Battery Lead Acid Slave Board

Postby dillond666 » Wed Feb 23, 2011 12:08 am

I have made up a test rig using two picaxes and the el cheapo LED / phototransistor fibre optic assembly.
Using the simple transistor amplifier on the receiver end has allowed a reliable 100ms pulse to be transmitted and received.
This is all I need to get my slave bus running fibre optics on the cheap 8)

I then reconfigured the receiver to omit the transistor amplifier and connected the phototransistor instead to the input of the LM393 comparator. I connected a potentiometer to the other input to allow adjustment of the threshold. With a little tweaking I was able to get a good TTL level squarewave out of the comparator. I tried to communicate using 2400baud serial but it didn't quite work. The problem is that the slow rise and fall time of the phototransistor mashes up the serial signal so no matter where I set the threshold I can't get reliable comms.

Perhaps an op amp before the comparator would help? I'll also need to double check I'm driving the led as hard as is reasonable.

Derek

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Re: 8 Battery Lead Acid Slave Board

Postby retepsnikrep » Wed Feb 23, 2011 6:36 am

Nice work.

Reduce the serial speed. I believe the picaxe supports 300-600 baud.

Put a 1-10K pull down resistor on the photo transistor output.

Some of the picaxe inputs are schmidt trigger try one of those.

Use pulseout / pulsein instead of serial. Transmit different length pulses rather than lots of high/lows then response time is less critical. I did try that in one of the master/slave versions some time ago and it wasn't bad.

My earlier thoughts on pulsin pulsout are here

viewtopic.php?f=53&t=2060&p=15714&hilit=pulsout#p15714
Regards Peter

Two MK1 Honda Insight's. One running 20ah A123 Lithium pack. One 8ah BetterBattery Nimh pack.
One HCH1 Civic Hybrid running 60ah A123 Lithium pack.


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