7circle wrote: I thought at first you where just adding the bits to a spare board as you only need one in the circuit.
Actually, we need 2, one at the start of each sub-pack, and we want to use the link software to measure the shunt current. This circuitry will go on one or two boards per panel, so every 34th or every 17th board will have this circuitry in place of the end-of-row isolation circuit. End of row is only needed at ends of rows, never at the beginning, and the diffamp circuit will be at the start of a string of 8 or 9 BMUs (on one panel). For ~98% of the boards, there will be nothing populated in the diffamp/end-of-row area.
But your Pin1 uTxm on IC1 has swapped with Byp on Pin6 and the designators are all different. (R8,9,10,11,15 .. and others)
Fairly recently, we did a 3-wire rotation of the bypass and two transmit wires. This is so that we could take advantage of an internal inverter, so that the timer could generate differential drive without external components. Those boards are busy enough as it is.
The shunt diffamp output connects to LI, so we can use the link software to measure shunt current.
Looks like your putting the CellV straight in with out divider.
(Sorry I'm nosey)
? There has to be a divider; the reference voltage is 1.5 V, and we want to be able to measure up to 4.096 V.
Is its based on this one Rev 32 in your linked post?
Heh, close. We're on rev 45 now. In particular, the LI (link input) signal is a voltage divider to Vref+ so we can measure positive and negative link voltages. I think it's time for a (hopefully final!) circuit and layout.
I take it the JP11 is not connected for Current Sense.
It must be for Cell No 1.
It wasn't for a while, but Weber correctly insisted that it is, so that when the diffamp circuitry is there, the BMU can still be used as an ordinary BMU.
200A is 50mV on Shunt so thats 10x gain for 500mV
Believe it or not, those shunts are hard to source, at least at a reasonable price. Jaycar has some at a reasonable price, but they are 1mR, which means way too much dissipation (58W) at 240 A. There are 50 mR and 75 mR shunts, but its hard to find someone with them in stock. But we can easily juggle the resistor values for any particular shunt and maximum current. We need to get these things prototyped as soon as possible, since BatchPCB takes weeks. We could pay more for quicker turnaround, but we have so much else still to do that it isn't worth it.
You could fit a cap on R8 and pull pin to GND for RC filter.
Your Filter is at 1/T=f=1/RC = 1/(150k x 100n) = 66kHz @3dB
Not sure if my calc is right.
I think it's 66.7 Hz, not k
The is it worth clamping Op- and Op+ with diodes.
I think that surely the op amp has diodes (possibly parasitic ones) already.
So will this be a separate board or more parts as options on the ONE multi-purpose BMU-Link PCB?
This is a circuit that replaces end-of-row circuitry on some boards of a panel. We have a new Protel database file now that has two schematics and two layouts. When we generate the pannelised artwork, we'll do the juggling to make some of the BMUs specialised for the shunt diffamp. We decided it was simpler that way, and we don't need to carry sensitive analogue inputs that are tied to the negative end of the string off the BMUs and isolate them specially. Well, we'll have to connect the shunt wires specially, and they will need their own connectors and are potentially lethal, but at least they're not MPU inputs. If there is an accident, the opamp will possibly protect the MPU. We hope.
Ohhh its just a separate board just for the SHUNT not cell connected.
As above, no, it's a regular, working BMU that happens to be at the start of a half-pack.
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