Our NiCD Force Conversion
Extending our Force's Range with Advanced Batteries

Page 4, "Play it cool"


It was now May 14, and given that I was waiting for the new electrical cable, I decided that the next logical task was to move ahead on the battery cooling system.  This is a critical part of the NiCd system, as it keeps the battery modules cool during charging and when being driven hard.

I had already picked up a new Metro radiator from radiator.com, an internet supplier that obviously specializes in automotive radiators, and I found a used Metro radiator fan/shroud assembly from another online automotive parts dealer.  These actually all showed up months ago, when I was just getting started on the project.  It's embarrassing to admit that all this stuff sat around for months.

I did a quick analysis of the radiator installation and drew up a list of parts I thought I'd need for the job, and went on a parts run.  A stop at the local auto parts shop just down the street with the radiator in hand, and I picked up a piece of radiator hose with two elbows that looked like they'd be what I needed.  Next was a run to the True Value hardware store and a raid on the plastic barbed hose fitting bins.  Unfortunately, they didn't have enough stock of a few sizes I needed, so it was off to the Ace hardware in nearby Grafton.  They had many more fittings in a special display for some reason, and I cleaned them out of certain items.  Still, I was short on the 5/8" parts needed for the main hose.  Time to run to the Grafton Home Depot.

Between the three suppliers, I was able to build an impressive stockpile of barbed hose fittings.  I also got a huge supply of spring hose clamps, most from our local True Value store.  For some reason, they had a large number of them, and I was glad because I wanted to have all the major connections fitted with the clamps for safety.

Another thing I needed was a set of bolts to attach the finished radiator assembly to the underside of the car.  Like Solectria, I was planning on using the fuel tank mounting points just forward of the rear axle to attach the radiator and pump, and the Metro service manual didn't say what kind of bolts were used, they just gave a part number.  I tried hand-inserting 1/4" (too small) and 5/16" (too large) bolts, so I decided the threads had to be metric.  Another trip to the hardware store established that they were in fact 7mm.  It was questionable because the threaded inserts were pretty rusty!

I attached the fan/shroud to the radiator and also fabricated a set of aluminum brackets that would be used to secure the radiator assembly to a mounting plate, and whipped up a template made out of scrap 1/4" plywood that I'd use to mock up the mounting plate, which would eventually be made from aluminum sheet.

Radiator/fan on plate mockup

May 15: I fabricated three aluminum brackets that would be used to attach the radiator assembly to the fuel tank mounting points and bolted them to the car.  These are about 3" long, and made from 1" x 1/8" aluminum strip.  I continued work on the radiator, cutting and fitting the two rubber hose elbows to the radiator.  I made quite a few trips under the car to measure clearances and hold the mocked-up plate to verify the fit.

May 17: With the radiator plumbing more or less ready, I went ahead and built up the manifolds that would sit inside the rear battery box and distribute coolant from the main 5/8" hoses to the 1/4" hoses that run to the individual batteries.  I had seen a similar approach used by another EV with the NiCd batteries and it made sense.  Each manifold was made up of 3/4" PVC pipe fittings and had a 5/8" barbed inlet and six 3/8" outlets, with the threaded nylon barbed fittings sealed with black silicone sealant..

The order from West Marine arrived today and I built up the various interconnect cables I needed for the rear pack, then installed them.

Rear interconnects complete

I also picked up a couple of G-B 2-gauge electrical cable splice kits at the local hardware store.  This is basically a brass tube with a couple of screws and a heavy-duty heat-shrink cover.  I fitted it onto the interconnect cable between the front and rear packs with my extension (about 2'), tightened the screws and soldered it in place.  When that was done, I slid the heat-shrink tube over it and shrunk it down with a heat gun.  It's shown below prior to being covered.

Main interconnect splice

May 19: It turned out that in addition to the main front-rear battery interconnect needing to be lengthened, I had to also lengthen the 10-gauge battery charger cable to the positive terminal in the rear pack.  No problem, I had a lug and some appropriate wire on hand.

Next up was to figure out how to mount the coolant pump to the radiator mounting plate.  I didn't get any detailed sketches of this from Solectria's NiCd car, so I was totally winging it.  The main thing was to have a secure mounting that didn't transmit a lot of vibration into the vehicle chassis.  My solution, after many hours of fiddling with various orientations and locations, was to fabricate two clamp-type brackets that would have rubber bushings between them and the pump body.  I bought a 3" rubber pipe joiner, which has a thickness of 1/4" -- This would be a perfect bushing material.  The clamp straps themselves were made from 3/4" x 1/8" aluminum, bent around a piece of scrap pipe about the same size as the pump with the rubber bushing in place.  These were bolted to a threaded brass rod that would act as a standoff from the mounting plate.  I attached the PVC pipe fittings that would connect it to the radiator hose and the 5/8" main coolant hose, and did a test-fit of the assembly on the wood mounting plate mockup.  A quick slide under the car with the assembly verified that it would fit perfectly.

Finished pump assembly   Pump and radiator on plate mockup

May 20: Now that the mounting plate mockup was finalized, I cut the real thing from a sheet of 1/8" thick aluminum.  Using the plywood template, I located and drilled all the bolt holes and cut the opening for the radiator grille.  When finished, I bolted everything to it, put together the proper wiring harness and connector, connected the cooling hoses and hooked it up to a 5-gallon bucked filled with water as a test.  I started up the unit and it worked perfectly, pumping the water at an impressive rate.  With that test out of the way, I connected the real hoses and mounted it under the car.  Photos below:

Plate template on sheet aluminum Template clamped to plate for hole cutting Finished cooling system plate
Protective aluminum screen mounted on plate Finished radiator assembly, almost ready for mounting Radiator mounted under car

Also on this day, the special Saft temperature sensors arrived.  These are custom NTC (Negative Temperature Coefficient) parts that fit into pockets on the sides of the battery modules.  There is one in each battery compartment, and they are connected to the Brusa battery charger so that it can adjust its charging profile as the batteries warm up or cool down.  I had left certain battery connections loose so that I could slip the sensors into place.  The only trick with these was that the electrical connector was some sort of special one that I couldn't find a mating part for, so I cut it off and soldered the sensors to the existing temperature sensor wires that were in the car.  Once these were taped in place, I slid the battery modules into their final positions and completed the electrical connections to the modules.

Saft temperature sensor in battery module pocket

May 21: Today I ran the two hoses down from the rear battery box to the fan/pump assembly under the car.  I also routed two 5/8" hoses from the fan/pump assembly to the front battery box, fabricating special aluminum clamps that would hold the hoses securely under the car in the "tunnel" in the middle.  The only hassle here was that the best place to secure these hoses under the driver and front passenger seats was the plate covering what used to be the shifter opening in the floor of the vehicle.  Removing these bolts to attach my brackets turned out to be a big job because these bolts are used to secure the Solectria power selector!  I wound up taking a lot of time to get this properly attached.  I also replaced the original bolts used for this (steel) with stainless steel bolts, as the originals had rusted pretty badly.  Next I moved to work on the battery charger's connection to the amp-hour counter.  For this, I was going to need three wires.  Fortunately, my previous battery pack had a five-wire harness running to the front battery box as part of the battery monitoring system.  I simply brought these wires into the car through the firewall and behind the dashboard to the general area of the amp-hour counter box, which sits just below the steering column.  Three of these wires would be used for the amp-hour connection to the charger, and the other two would supply power to the cooling system fan and pump.

May 22: Today I installed the threaded inserts that were needed to receive the threaded rod that would hold down the front row of batteries in the rear battery box.  These went in very easily.  With these in place, I went ahead and installed all the battery hold-down bars in the rear battery box.  These are 1" square aluminum tubing, positioned to fit perfectly in the spaces on the tops of the Saft battery modules.  I placed a small piece of foam padding between the bars and the tops of the batteries to prevent damage from the rigid bars.

Rear battery hold-downs

May 23: In preparation for finishing the front battery box, I extended the positive main battery lead using one of the GB splice kits (see above).

May 24: Today I finally installed the rear cooling manifolds and connected all the tubing to the rows of batteries.  This completed the cooling system work in the rear battery box.  Whew!

Rear cooling manifolds in place  Rear cooling plumbing complete

I then moved to the front battery box and wrapped up the cooling system connections there.  This was a royal pain in the you-know-what, because the front battery box is a lot more constricted than the rear one.  There's not a lot of room to route the little cooling hoses and the last thing you want to do is pinch one so that it doesn't allow the coolant to flow.  Well, it took a lot of fussing and a last-minute redesign of the hose routing, but I got all the hoses connected and conducted a little pressure test.  It all tested OK, so the next thing was to officially fill the thing with coolant and get it ready for charging!

Let me tell you something about me and liquid.  We don't mix.  All through this project I was ultra-paranoid about making sure that every fitting in the vehicle's cooling system was perfectly tight and wouldn't leak.  I used dozens of those spring hose clamps, because I've seen the screw-type hose clamps fail.  Well, for once I got lucky in that department because I didn't have any leaks when I filled the system.  I also didn't have any flow because the pump kept getting airlocked.  Forget what they say about water always seeking the lowest level -- that's a big lie!  My pump was at the lowest level in the car, and I had no flow.  The main coolant lines are transparent, so luckily I could see where the green fluid (Sierra antifreeze and water) wasn't going.  Namely, the pump.

OK, I had figured this wasn't going to be easy, so I jumped on the creeper and rolled under the car with a socket wrench.  I removed the three bolts on the radiator assembly and dropped it about a foot, setting it on a spare cardboard box so that the liquid was flowing into the pump.  I restarted the pump and watched as the liquid gurgled in and air gurgled out of the other end.  More air came into the pump as it was flushed out of the upstream batteries and I had to jiggle things a bit to keep it moving, tilting the radiator so there wouldn't be any air left in it to cause problems later.

The trick was, I was dealing with a double-loop system.  Coolant comes out of the radiator, gets split into two loops -- one to the front battery box, the other to the rear -- and then it works its way back to the pump, where the two loops are combined back into one hose.  Now, the front coolant loop was an open loop, with a big 5-gallon reservoir bucket sitting next to the front of the car with its hose running to the pump side and a hose coming out of the radiator side running into the bucket, so any air coming out of the radiator would bubble out into the atmosphere, and only coolant liquid would go into the pump side.  The rear coolant system was another story -- It was a closed loop because I didn't want to have to mess with closing up the loop in two places later and risk getting air into the system.  Any bubbles in the rear loop wound up coming back around to the pump side, and had a 50-50 chance of going back into the rear loop when they came out of the radiator!

Cooling system schematic (click for large version)

So, the trick was to make sure any bubbles that came through the radiator went toward the front of the car, where they would be removed from the system by the bucket.  To do this, I sat under the car with a quick-clamp and watched as bubbles went into the pump, and when they did, I clamped down on the loop going to the rear batteries.  This forced the coolant to flow toward the front of the car, removing the bubbles.  When the coast was clear, I removed the clamp.

Believe me, there is a lot of air in a system like this, as the empty coolant pockets in the batteries are replaced by fluid.  It took several hours before I was satisfied that the system was clear of air.  I then re-mounted the radiator and pump under the car and called it a night.

NiCad Conversion, Part 5

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This page last edited August 06, 2002