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[Reply #15 on:]

Yep, that's exactly what I was suggesting, pity there's no UART in the small AVRs and the 2313 doesn't have an ADC I think.

That would be a very simple circuit (you have 1 pin left for the temp sensors as well).

FWIW I have the same thing (but not isolated) planned for a monitoring gadget I'm working on, albeit with slightly larger (32-bit) processors.

______
Rob 

[Reply #16 on:]

Stringing all the battery monitors in series as Crossroads suggests cuts down on opto isolators (which could be reduced to 1 per board), however it has the disadvantage that if one board fails, the whole string fails and you can't immediately locate the fault. Having the boards individually addressable mostly avoids this, because most failure modes of a single board won't cause the entire system to fail, they'll just cause that board to fail to respond.

[Reply #17 on:]

That's true, in my system I have a method to bypass a faulty node.

I think the above would be reliable enough for this application, but it is one-out-all-out. Maybe a watchdog and an error light so at least you'd know which one was faulty. The error signal could be used to hold in an analog switch/relay so a faulty node was automatically bypassed.

I guess it's a tradeoff between code and hardware simplicity. Or go back to one of the MUXed ideas, I just hate the idea of 40 wires though when 1 can do.
______
Rob

[Reply #18 on:]

Anyone noticed that the OP appears to have gone away. This is possibly all too much for him.

[Reply #19 on:]

I'm still enamored of the idea of just wire-ORing 40 open collectors from optoisolators with a receive-end minimum-but-workable pullup, and allowing the occasional collision.

I would like to be able to replace any battery and (usually, in most failure modes) keep working even if one battery monitor dies. The higher level should be able to alarm when a battery is just not heard from for a minute or so..

And the hardware is simple.

Hmmm??

[Reply #20 on:]

Anyone noticed that the OP appears to have gone away.

Yep, that often happens when a project is not as simple as first thought I guess.

Having said that it's not rocket science and every time this pops up we go over the same 3-4 methods.

Maybe someone should design a working system then we can all move on

______
Rob

[Reply #21 on:]

After reading the comments, I think we can come up with a system that could in parallel and be break proof also.

Every card is collected open collector style to a master data line.
Every card also monitors that line to see who is talking when.
Still give every sender and ID, and work out a protocol so that they only transmit when its their turn.
Find a data rate that is workable with these loads and split up the time from there.
Not what this darlington opto is capable of driving, and maybe the incoming opto needs to be a sensitive one to keep the overall current load down.

Connecter use could be optimized, just picked convenient to show package, and probably the thermistor also, I just grabbed one to show it.

I think I have it set up so that a High out of the ATTint is seen as a high back at its listening port.
This card could be wired in parallel, and will also support the serial wiring I posted earlier where one card drives its neighbor.

What say ye that have worked with opto's before?

[Reply #22 on:]

Hey,

Only concern is all those receiver LEDs draw current.

All those open collectors have very low leakage; no problem.

Maybe with 6N139's watching the bus to try to avoid collisions only, or read relatively low baud rate.

?? Hmmm.

[Reply #23 on:]

"all those receiver LEDs draw current"

That's why I picked the darlington output.
Guess its time to look up some specs and see what these parts can actually do.
Maybe a heftier output transistor is needed.

I'm out fora while ...

[Reply #24 on:]

give every sender and ID

I think this is an issue unless there is a method to do this in the field. Units need to be easily replaceable.

work out a protocol so that they only transmit when its their turn.

Given that each node now monitors the serial line you could do as you say and have a protocol driven by the master. You could also though use Terry's idea of slaves just transmitting whenever, because they can now monitor the signal they know if the transmission was corrupted so they can try again.

However it's done the system needs to allow for 48 (lets say 50) batteries. That allows it to be used with a 96v system and 2v batteries or something like the OP's system of 40 batteries

So 50x say 10mA = 500mA to drive the optos, that's a lot for an opto I think. I haven't used optos much but I'd say using a darlington for the incoming opto would help. In fact the outgoing one probably doesn't need to be a darlington.

Another option is isolated RS485.

______
Rob

[Reply #25 on:]

I apologize for not responding to all these comments earlier. The thread did not seem to gain any interest at first and I have been talking to dc42 by email. I'll be honest this is all way over my head , but that will not stop me from trying.... I ordered a mega board, project board with jumpers and 5 sample ti battery chips. The big issue with these chips are cost. I will look at all of the ideas offered and try a few variations till I find a solution that works and is inexpensive. (will be a great learning experience for me as well)....


Luke

[Reply #26 on:]

The big issue with these chips are cost

They look like fantastic chips but they do a lot more than you seem to need.

______
Rob

[Reply #27 on:]

It isn't that I wouldn't use more of the functions of these chips but the problem is I am using 1250 ah batteries and these are good to 327 ah. I only want to use 40 at first and looking online these are going to cost in the area of 10-12 each. If it is going to be easier to use these then I will. I am curious what is going to be the easiest setup for such a newbie as me  

Just to clarify, this is for 40-1250 ah sla batteries in series.

Luke

[Reply #28 on:]

Hmm, okay I was thinking 12V lead-acid batteries with lots of capacity.
More info to start would have been good.

Give up some more info - what is this thing installed in, how are the batteries recharged?

I don't understand this:
"I am using 1250 ah batteries and these are good to 327 ah"

[Reply #29 on:]

The ti battery monitoring chip [/url]http://www.ti.com/lit/ds/slusaa0/slusaa0.pdf[/url] is rated up to 327 amp hour rated batteries and I am using 1250 ah batteries.
These are used with a large ups unit (multiply 40 battery strings). The ups units are 500 kva rated units. Charge voltage is 13.3 volts on float and peak at 15.4 volt on recharge times that by 40 on a string.
One other function I would like to add would be measuring internal resistance. The way we test in the field is with an ac tester in mv. Now I would guess that you guys have a more exact way to test for this. This is not absolute, but would be great to detect a bad battery early.

Luke