I've now built & done basic testing of all 5 boards. Although I haven't completely wired my unit up, I feel confident enough to post the circuits & pcb layouts.
Component numbering now matches the boards, and the circuits should match the pcb's as built. Pcb files are in protel Autotrax format. Boards are all single sided, some with more links than others.
Commercial rights reserved. You can build one or more for yourself, the guy down the road, your dog, the guy down the road's dog, or even the pizza delivery lady. What you can't do is ship the design to China and make million$.
It can be built in stages, and you don't even need to build all 5 boards if you don't want all the features.
Although I have specifically targeted the design at 24 volts, it can be readily adapted to other voltages.
I've done all the interconnecting with ribbon cable, or 0.1 inch headers & plugs. It could be hard-wired, but I definitely suggest you follow my lead.
Photos of the completed unit in about a week.
Not a newbie project. You need to be able to make printed circuit boards, and be fairly competent at things electronic to build this.
BOARD 1.
Contains the LM3914 expanded scale voltmeter, driver transistors, and voltage regulator. The regulator is 5 volt, to suit the cmos logic on the other boards. It may need heatsinking. I've calibrated mine to read from 27-28 volts in normal mode, and 28-29 volts in boost mode. Selecting boost mode can be done with a simple switch, or from the timer board. It is perfectly reasonable to build a minimalist system using just this board, calibrated to read say, 20-30 volts, and using just the top one or two outputs to turn on fets.
Circuit
Pcb
BOARD 2 (Latch).
Contains a 74HC374 latch, clocked by a 555. This means the fets turn on or off at 30 second intervals. With this, you can use things like pumps as dump loads, without fear of them turning on & off very rapidly,and not doing them any good.
Circuit
Pcb
BOARD 3 (Timer).
Plugs into Board 1 in place of the manual Normal/Boost switch. Has push-buttons for start & stop, and the timer will stop boost mode after a pre-determined time. I've set it to run from 15 seconds (for testing) to 8 hours. Steps are in binary(8hrs, 4hrs, 2hrs, etc). The board is laid out so you can run ribbon cable to a rotary switch, or just use a jumper to select a fixed time & leave it at that. There's also an accumulate mode, so that the timer will only run while the battery voltage is at or above at least the first led.
The battery temperature board also plugs into this, and will terminate boost mode if the battery temperature exceeds a preset level.
Circuit
Pcb
BOARD 4 (Battery Temperature)
Circuit
Pcb
BOARD 5 (Alarm)
The 74HC86 exclusive OR gates monitor the gate & drain of each fet, and raise an alarm if they are not as they should be. So an open circuit dump load or a short circuit fet will raise an alarm immediately. An open circuit fet won't raise an alarm until that particular fet is turned on. There is an audible alarm, and a mute switch. The alarm led wil operate as soon as the mute switch is operated, so you can't accidently silence the alarm without visual indication. There is also a connection from the 10th led on board 1 into the alarm circuit to function as an over-voltage warning. On a correctly sized system, this should never happen.
Circuit
Pcb
Amanda