Since the Zivan charger is prone to overcharge the batteries, I bought a set of Rudman Regulator MKII's from Manzanita Micro and installed them. These are bypass regulators that will bypass current around a battery if it has reached full charge. Each regulator has a pair of very useful LED's on them. A green one to show that the regulator is bypassing current (i.e. the battery is charged), and a red one that shows when a battery drops below a set voltage. (Showing it's getting too low, and you shouldn't be driving more on it! Mine are set to 10V.)
Having these LED's hidden in the battery boxes isn't especially useful, so I moved them into the cabin of the Sparrow. This meant I had to unsolder the LED's from the regulator and solder in a plug for each one. I then built a bracket to hold all the LED's, and ran wires from each regulator to them.
Another minor problem is that the Sparrow battery boxes have very poor air circulation, so the regs are likely to overheat and shutdown - which prevents them from saving the battery from overcharging. To fix this problem I bought a bunch of surplus CPU fans from Marlin P. Jones and mounted one to each fan. I also mounted an NPN transistor and wired it in to turn the fan on when the regulator comes on.
Joe Smalley gave me the following information on how to do this:
To run CPU cooler fans from a Mk 2 regulator. Use an emitter follower off U1 pin 7. Collector goes to +bat (J2). Emitter goes to the red wire on the fan. Black wire on the fan goes to -bat (J6). Some fans will benefit if a capacitor is put across the fan leads. There is a schematic at http://www.manzanitamicro.com/fan circuit.gif The transistor not very critical. It must be an NPN that has a voltage rating at least 20 volts and a current rating large enough to carry the fan startup current. The dissipation rating should be at least 2 watts per amp of fan current. If you have a 100 milliamp fan, the transistor needs to be rated to dissipate 200 milliwatts.
This is a shot of a modified regulator. You can see where I removed the 2 LED's and soldered in 2 pin plugs. The fan is held to the heatsink with a pair of nylon ties. The transistor is glued to the far side of the fan.
All the regulator LED's are mounted in a strip of angle aluminum just above the Big Red Button. I just drilled holes and glued them in. I ran a pieced of 4 conductor phone wire from each reg to each pair of LED's. The wire plugs into the reg, and is soldered to the LED's.
This shows how I put the regs on top of each battery under the seat. All the gray wires are the phone cable running to the LED's. I did drill a 1" hole in the fiberglass at the bottom of the window well behind the panel, so I could run all the cables through. Make sure that the regs are placed so that any water draining from the window will NOT land on them! I also put a 1/8" piece of plastic under each reg so any water that flows across the top of the battery won't hit the circuit board. The white wires run to a contact strip I mounted to the back of the seat. This lets me check the voltage on every battery without removing the seat or opening the hood. 14 wires total.
This is the front battery compartment. Can't see much here. I tried to make sure the regs were placed so that water won't hit them. (I've pulled the plastic cover off the one so it can be seen.) The regs for the lower back 2 batteries are mounted to the side of the single battery, and the reg for the single is on top of it. The other 3 are under the Zivan charger.