Tried to catch you in IRC for some days, Bob... but you're not talking to me!
Serious suggestion. I've got (slightly) undersized wiring from classic to batteries. Not so much that it's causing excessive heating or anything, just a matter of what I had at the time, and space for cables etc.
The result of this is that I'm seeing up to 180 to 200 millivolts drop across the DC cable.
That may not SEEM like much, but double it for two conductors and suddenly it's a big difference. Especially when I'm running LFP cells.
My suggestion/request would be for the fairly minimal change to the controller to add + and - battery sense lines.
These could easily be internally coupled to the battery + and - cables via a sizable resistor (say, 1K) so they would not NEED to be connected, but if they were, we'd have an ACCURATE idea of what's going on at the batteries, not just on the terminals of the classic.
The obvious follow-on from that would be to add a modest constant-current source (hell, even just lower the 1K resistor to something like say, 220R) and we could use the sense line to pre-charge the capacitors and eliminate the "Bang" when connecting the classic to the batteries (eg, after a reset). (It's quite an inrush when you drop it onto a 52V battery!)
It would increase the regulation and accuracy of the whole system. (Talking with some others in IRC, it seems my issue is far from unique - others reporting similar drops. One has a CC from a different supplier, and it turns out his already has sense+ and sense- as a factory-fitted feature)
Agree with Ross -- on the systems here, can see about 400 mV drop in the cables from the Classics to the batteries. This is due to using fairly large toroidal inductors in an attempt to filter RFI generated by any MPPT CC.
Having no sense leads is not the end of the world, but would be nice, and with larger battery banks, the End current is still in the 10 - 20 amp range, so still a bit of an offset.
Ross, am surprised about the Bang that you mention. Use a real circuit breaker here, and it is not noticeable at all, when applying power to Classics. Large inverters are another matter. Using a 250 breaker, when applying power to a well-rested inverter, there is a noticeable " S P U T !!"
FWIW, Vic
Quote from: Vic on February 03, 2015, 10:01:16 PM
Ross, am surprised about the Bang that you mention. Use a real circuit breaker here, and it is not noticeable at all,
Well, yeah, the first time I did it I just dropped a lug onto the bus, to get it going quickly.
Of course now it's through a proper breaker, but the original event is still etched in my mind!
There is still a hell of an inrush current, breaker or not!
Quote
Large inverters are another matter. Using a 250 breaker, when applying power to a well-rested inverter, there is a noticeable " S P U T !!"
He!! yeah! My new inverter however very cleverly eliminates that by the "sense/precharge" wires as I mentioned above.
Ross, also note some reports of a voltage drop through some versions of the panel mount carling breakers.