Curtis 1231c upgrade: Binning Gate Drive Resistors

I am upgrading the power board of my Curtis 1231c DC PWM motor controller. It uses 18 MOSFETs to switch the power, and each MOSFET had a 47 ohm resistor on it’s gate input. The point of such a high resistance was to slow down the switching of the MOSFET’s so that they would all share the current somewhat equally and no single MOSFET would turn completely on before all of the others had a chance to start shouldering the load.

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Curtis 1231c Power Board desoldering

I desoldered all of the main power components (diodes, MOSFETS, capacitors) from the power board of my failed Curtis 1231c PWM DC motor controller. The plan is to upgrade all of the components to give it higher capacity; while producing less heat. Of course, to replace them, I had to remove the old ones, which took around 6 hours of work with two different soldering irons and a solder sucker.

My advice:
-Heat component legs (diodes/MOSFETS) from the top of the board (side with the component) while you solder-suck from the bottom. Get one leg completely free first, then work on the other. After you suck almost all the solder out, you may still need to re-heat the leg and push it away from the PCB with a small screwdriver so it doesn’t stick to the inside of the hole.
-For the capacitors, don’t be afraid to add a little solder to the smaller leg, and then use a 100 Watt super wide tip soldering iron to heat both legs up at the same time, and pull the capacitor straight out. Suck the solder from each hole individually later once all the components are gone.
-I heartily recommend the Engineers SS-02 Solder Sucker, the silicon tube it uses is great! I did get solder stuck inside the metal tip a few times, but nothing a 5/64th drill couldn’t fix right up.
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Curtis 1231c diodes: Diotec DR7506FR vs TSR2402R

I am looking to replace the MOSFETS, diodes, and capacitors in my Curtis 1231c with upgraded components. I unsoldered one of the existing TSR2402R (7103 K) diodes from the power board and tested it with my Fluke meter and bench power supply.

Here are my results:
Power Supply providing 3.2A, forward voltage drop: 0.776 volts
Power Supply providing 2.0A, forward voltage drop: 0.737 volts
Power Supply providing 1.0A, forward voltage drop: 0.697 volts
Fluke Diode Setting: 0.351 vdc

Average time for the button temperature to raise from 25 °C to 50 °C with a 3.2A current: 45 seconds

The replacement parts I purchased were from DIOTEC, specifically their DR7506FR model (the R at the end means “Reverse Polarity”, making them an exact drop in replacement in form factor and polarity). They were marked: “DT110  DR7506FR” plus a diode schematic. Here are my results for the upgraded component:

Power Supply providing 3.2A, forward voltage drop: 0.754 volts
Power Supply providing 2.0A, forward voltage drop: 0.700 volts
Power Supply providing 1.0A, forward voltage drop: 0.646 volts
Fluke Diode Setting: 0.399 vdc

Average time for the button temperature to raise from 25 °C to 50°C with a 3.2A current: 47.5 seconds

Of course, the original diode I’m measuring had been in use for many years (I estimate ~750 hours of driving time given the 22K miles) and was heated up as part of the soldering and unsoldering process, while the DR7506FR I tested was brand new straight from the manufacturer. After I unsolder a few more diodes I’ll check them to make sure their readings are similar. (I’ll probably also test a few other DR7506FR diodes from the bag as well.)

Of all the measurements, the temperature rise time measurement was the least scientific, as I was using an inexpensive non-contact IR thermometer and attempting to point it at a small button in each diode, waving it back and forth to find the hottest temperature. I took 4 measurements on each diode (alternating to let the other one cool down) and averaged them together. In general, the readings from the DR7506FR were longer than from the original TSR2402R with one exception. If I throw out that pair of readings, the averages would be 46 seconds vs 50 seconds. Given that the measured forward voltage drop for the DR7506FR was lower for any real amperage readings, it dissipating less power and taking longer to rise to 50 °C appears to be reasonable.

Curtis 1231c Replacement Power board components

My Curtis 1231C motor controller blew up some MOSFETs and died. I replaced it with a used unit to get my truck back on the road, but now I’m interested in repairing the one that died so that I’ll have a spare.

I might be able to replace the components that died with exact replacement parts (but the IXTH50N20 MOSFETs are hard to find nowadays, and the diodes are basically unobtainable) to get it working, but since I have it open and am doing all of this work, I am exploring alternative (new) components that will have higher ratings and possibly give my controller more capacity or at least more resistance to blowing up again.

Of course, if I replace one component (power switching MOSFET, freewheeling diode, or ripple controlling capacitors), I will probably need to upgrade the other two as well so that I don’t just move the weak link from the MOSFETS to the capacitors or diodes.

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Curtis 1231C-8601 500A PWM DC Motor Controller teardown

After replacing the Curtis 1231C-8601 motor controller that had failed, I opened the case up to figure out what had failed.  The controller hardware is inside of an aluminum extrusion with both ends “potted” with some black semi-flexible material (hard silicon perhaps?) that could be cut using a razor knife and a lot of effort.

Inside, there is a Pi shaped piece of aluminum extrusion that acts as the heatsink for the MOSFETS and freewheeling diodes, as well as being electrically connected to the motor – terminal. It is held against a large thermally conductive, but electrically insulating pad, which separates it from the controller case, but allows heat to be dissipated. It is held in place with 8 screws that pass through insulating plastic brackets into the bottom of the case.

People online had told me that these screw holes were “potted”, but on my controller they were just filled with two rubber plugs.They also told me that you could not cut through the Curtis potting material with a razor knife. [This super hard potting material was also prone to cracking at the edges and letting moisture into the controller, so a flexible rubber like material is better anyways…]

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LED Headlight Upgrade – 1995 Chevy S-10

The low beam in one of my headlights burnt out, and since it’s a 4×6 sealed beam unit, I have to replace the whole thing. I decided to replace both the driver and passenger side at the same time so that they match, and upgrade to LED units by GENSSI (4×6 G3) that also add the ability to have always on daytime running lights (DRL). (As opposed to always driving around with my low beams on.)


The (1995-1997) Chevy S-10 only has two headlight units and the factory sealed beam headlights (H6545) use a weird plug shape that is not the standard H4 (the ground plug is twisted about 45 degrees). They are rated at 65 watts on the high beam and 45 watts on the low beam, but for nighttime driving I have never been happy with their light output.

original_hp6545 95-97-chevy-s-10-headlight-plug


The GENSSI (4×6 G3) that I am replacing them with has a measured power consumption for one unit at 14.4 volts on my bench power supply of 1.8 A for high beam, 1.03 A for low beam, and 0.08A (8ma) for the DRL.  This works out to 26 watts, 15 watts, and 1.1 watt for a single unit. The eBay auction page claimed 25, 20 and 1.1 watts for high/low/DRL, so the measured figures mostly match the online specifications, giving me hope that the specified lumen ratings may also be somewhat correct (Claimed at 2150/1800/57 lumens).

These units cost me $40 each, compared to the  $15 replacement cost for a direct drop in Wagner H6546.  However, the cost didn’t stop there, as I needed to pay an extra $30 for two adapters from the OEM socket to the H4 plug on the LED headlights. I could have just cut off the OEM connector and wired in a H4 socket for less money, but I decided to pay for the adapters to make the installation plug and play as well as retain backwards compatibility. Supposedly LED lights should last practically forever, but if I ever need to replace them in a hurry I want the ability to go back to the OEM 4×6 units which can be picked up at most auto-part stores.

The difference between the LED’s and the original headlights is quite apparent, as the LED’s are a “cooler”  color temperature (white, not yellow) and brighter, which is why I am changing out both headlight units even though only one burnt out.

Here you can see a comparison of the new LED on the left and the original halogen on the right, shining on a garage door in the day and at night.



I paid an $80 premium for the LED lights as opposed to the cheap OEM halogen replacements. For that $80 I get a cooler color temperature (for a more modern look), more light (better nighttime visibility), minor energy savings,  and the ability to wire in true daytime running lights if I decide to make the effort (not yet connected).

Inexpensive cooling ducts with hardware store parts for my dual chargers

In an effort to counteract overheating, I have added cool air intakes connected via 4″ diameter ducts to the fans on my TSM2500 (CH4100) chargers.


I used a 4″ flush to the floor “snap-in” PVC floor drain (designed to be cemented inside of a 4″ PVC pipe) spray painted flat black as my intake, connected to a 4″ aluminum flex dryer hose (mostly ran straight through, but the flex hose allowed me to vary the length) with worm screw clamps (a.k.a. hose clamps). The single most expensive part of the install was the 4″ hole saw ($15 on ebay, or $20 at the store). I could have saved $5 by going with a less expensive vinyl dryer hose, but I like the rigidity and appearance of the aluminum.



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TSM2500 (CH4100) Chargers Overheating

Twin Chargers in Box

Now that it is summer, and outside temperatures are reaching 26-35 C (80-95 F), my dual TSM2500 (Rebranded CH4100) chargers are overheating. After about an hour charging at full power, they reach around 74 C (165 F) and shut down. The ThunderStruck Motors EVCC records this as a “normal” end charging event (because the Amperage output goes to zero), and for some reason it triggers a ground fault on my EVSE (perhaps they have a thermal switch that shorts the charger to ground to shut it down, or maybe my JuiceBox Pro 40 is just overly sensitive?)

I guess the overheating is to be expected, as the chargers are in a five sided box (with only the top open) and mounted to a piece of (thermally insulating) plywood. Although there is a tangle of wires in front of them, the wires really don’t interfere with the airflow as much as it looks like from this top view.

In my defense, the charger’s manual (v. 1.05) specified that I should leave a 50mm (2in) gap in front of the charger for proper ventilation and I left around 8 inches. It also noted that the “Working temperature” for the chargers was -25 to 55 C (-13 to 131 F). It didn’t mention anything about thermally bonding the charger to a heatsync.

As a temporary solution, I have re-configured my 80% charging profile to only run at 1.2 kW (8 amps total, or 4 amps per charger on a 128-131 volt pack). This is about 25% of the 15 amp max power that the chargers are capable of in cold weather. At this relatively low power, each charger is outputting just over 500 watts, and even in 32 C (90 F)  weather the charger temperature hold steady at 50 C (122 F).

Charging at one kW may not sound terribly fast (it’s not), but this workaround is actually fine for 95% of my charging needs, as I rarely need to refill more than 8-10 kWh (20-30 miles) per day of use, and L1 charging overnight works fine for most of my needs.

However, I purchased the dual charger setup so that if I was necessity charging away from home I could charge at a 4 kW rate, so I want to make improvements to my cooling so that I can run the chargers at full power (without them overheating after an hour) if needed.

ThunderStruck Motors suggested that I mount the chargers to an aluminum heatsync, which is a good idea, but difficult and costly to implement.

I have decided my first order of business is to drill two 4″ air intake holes into the bottom of my charging enclosure and duct them to the top of the chargers right over the fan using dryer hose. This will allow the fans to draw cool(er) outside air directly over the vanes on the charger, and keep the heated exhaust air from mixing with the cool(er) incoming air. Since the top of the box is open, the heated output air should have no problems escaping, as convection will assist the fans in exhausting the hot air upwards.  If adding intake air vents doesn’t solve my problem, then I’ll worry about making an alunimum heatsync plate to take the place of the plywood.