Several people have enquired about this gadget, so here is a short description of what it does. Due to that interest, I may now get around to finishing it off and maybe offering it as a kit or built unit.
When you've got batteries in series, you can't be sure if one of them is under-performing unless you measure the voltage under load. The most simple way to do this is to hook up a load to your battery pack, to draw 100Amps say, and check each battery with a volt-meter. But it is nicer to have a read-out of the individual battery voltages while you're driving, or more importantly, of the lowest battery voltage - that way you get advance warning of impending failure and have time to swap out the bad block or condition it back into health.
So I decided to build a simple unit to sample each battery voltage, and display the information on an LED display.
But by the time I got around to building a prototype, the feature list included:
The hardware consists of an aluminium box, roughly 10"x8"x2.5", which is mounted in the engine compartment. There is a large Molex connector to which a wire for each of up to 16 batteries is connected (plus one) - these wires have an in-line fuse holder where they connect to the pack. The voltage regulation is done rather crudely by switching in 3A bypass loads at a user-settable voltage (this should be based on the pack temperature, but isn't, yet). Those resistors are inside the box, so there are two small fans to help move the heat away.
The power supply is taken from the vehicle's 12V system, but this is not connected with the pack.
The charger cutoff is very simple, it just sets an output when all the regulators have "lit up", which should un-latch the charger's mains relay. I don't think it's a good idea to move any charger functionality out of the charger, but this feature is useful and cannot cause batteries to be over-charged - at worst a failure would result in an un-charged pack.
The standard display is a 4 digit LED readout, a 5-bar "% charged" indicator, and a rotary switch to choose between:
Not all of those functions are perfected yet!
There is also an RS232 connector, which plugs into a Palm-3 cradle (should work also with any other Palm or Handspring PDA).
The software for this is even less finished than the main box, the following list shows what it does do, and what I would like it to do:
But what are those user variables? Several customisable settings, stored in EEPROM which are set according to the vehicle and the battery pack installed. These relate to battery characteristics (Peukert's constant, and measured capacity, for example), scaling factors for the various sensors, and all the threshold values are accessible via any RS232 terminal connected to the serial port, and a simple text interface similar to the Hayes AT command set for modems.
The Palm software uses this same interface but can also cope with the large amount of real-time data which can be sent, and presents everything via a GUI.