First outing, running on three cylinders. Solved.

[anthonym]

yes, thought you would be along ;-)

[anthonym]

we never did resolve why the .27A seemed not to be enough to drain the batteries so fast, but I think I just left them unattended for longer than I think I did, because the remaining wires on the positive show zero drain. 0.00 at all decimal places.

[revilla]

So what we think has been happening is:

Anthony's Brise alternator has a separate sense wire that can be run directly to the battery to compensate for voltage drops in the charging wiring and allow the alternator regulator to regulate the voltage at the battery directly. However if this sense wire is held at battery voltage when the main battery wire is disconnected, the internal circuitry of the voltage regulator (confirmed by Brise) results in a current draw of about 0.27A on the sense wire, which over a small number of days flattens the battery.

The battery is then left standing in a discharged condition for a while which does permanent battery damage. It appears that this process has killed a number of batteries to the point where they will no longer even hold a reasonable charge overnight, giving the impression of an even larger current drain.

The issue only occurs when the B+ wire is disconnected from the battery by a master switch but the sense wire remains connected.

The solutions are i) not to pass the alternator B+ through the master switch, which is generally unacceptable. ii) connect the sense wire downstream of the master switch, which is the "correct" solution from a safety point if view but which partially defeats the aim of having the sense connection as some of the voltage drops will be outside of the sense loop (although it probably makes very little difference in reality). iii) Leave the sense wire disconnected, which the alternator supports. Obviously this completely disables the sense circuit but it's no worse than the way most other standard alternators work.

[Paul Deslandes]

In the spirit of making things as complicated as possible you could connect the sense wire to the battery via a n/o relay, the coil of which is connected to the cold side of the cut out switch (and ground of course), thus ensuring that the sense wire is connected to the battery when the car is running but isolated when not.  But as you say Andrew, it probably makes the square root of no difference in reality given the loads drawn by a seven's electrics; and it introduces another source of potential (sorry!) failure, not to say additional weight.

Paul

 

[anthonym]

what about a relay introduced into the sense wire, activated by the cut-out switch accessories or even the ignition? or does that interfere with the voltage reading?

I am seeing if the battery that was connected all Winter can be brought back; it says it is charged, but so do the other "dead" ones (except one that won't accept charge at all staying at 6.x volts). One of the Banners was faulty I think based on the rusty coloured acid in one of the cells. I will be pleasantly surprised if the over-Winter one comes back, but we will see. I now realise when I thought it was goosed last year, it wasn't it was being drained. 

wondering if there is some gadget or way to identify parasitic drain in a trivial manner, like the voltage gadgets we (now) have. That said, any time I find my battery flat, my heightened awareness will do the trick before consigning a battery to the bin (read recycling).

Here are my notes about these five batteries, not including the one with rusty acid:

time of day on the left, Voltages the rest

I imagine it might only make sense to me..   sense ;-)

 

@Paul complicated is fun :-)    - interesting same idea about a relay.

[revilla]

@Anthony complicated is unreliable :-( or seems to be on your car!

@Paul: Yes, the technically "correct" solution indeed. But I think we are both agreeing that it's an academic exercise at this point. Anthony, just disconnect the sense wire or take it back to that downstream terminal post, forget it and get out in the sunshine!

I don't think you need to worry about having an ammeter or anything to warn you if you suddenly get a current drain. Your car didn't spontaneously go wrong, it was wired up wrong in the first place - which I may have played a part in, and if so I apologise for not spotting the error. Once sorted it will be fine and will stay fine.

[revilla]

I imagine it might only make sense to me.

Yes  

[anthonym]

yes, currently disconnected and heading out in to the sunshine, next outing to exceed the three minutes of yesterday's. 

I have noticed my alternator does not charge at tickover, but it does charge at a n y t h i n g above tickover. So two choices (1) install the smaller round thing (what is that word?!!) pulley I ordered for this problem before I realised how close it is in revs (2) increase the tickover by however many revs it needs (3) do nothing and hope (4) do nothing AND install the sense wire correctly to maximise charge efficiency when it is charging; I gather half a volt can make a big difference as regards keeoing the battery charged. 

two choices ..

[anthonym]

andrew you said a longer connect from sense wire to battery pos will make zero difference.. in whihc case simple attach to distribution post solves it n'est pas?

 

the reason I haven't done that is the wire is too short and the ring connect too small and the sun is shining.

[revilla]

A variation in option (3). Do nothing and stop worrying about it. I can't imagine an R500 spends much if it's life at idle speeds?

[anthonym]

not willingly, but rarely a French traffic jam .. although that does other damage because of zero airflow