Elec-Trak DC-DC converters.

I love my Elec-Trak lawn tractor. It’s about 50 years old though, and the lead acid batteries are not very cost effective anymore so I upgraded them to Lithium Iron Phosphate batteries and also added an inverter to run my shop if the power goes out.

If you also have upgraded to lithium, you’ve surely noticed that there is an issue with driving the 12V lights and the 18V lift motor; lithium packs can’t handle the imbalance of mid pack power taps. DC-DC converters are the answer, here is how I used inexpensive units from Amazon on my E15.

I used a 10Amp unit for the lights:: https://amzn.to/3BKPeEi
I modified this 20 Amp one to put out 18V for Lift motor: https://amzn.to/2WN8cLD
using a 5.1k 0603 resistor like the ones in this kit: https://amzn.to/3BLdbLl
(any 5.1K ohm resistor should work if you can manage to fit it in there with fancy fingerwork)

In retrospect it seems to me you could use two 20 Amp units for both applications for a slightly higher cost. I did the lights first and then ordered the Lift DC-DC so I didn’t think of this. I probably would do this next time.

Lights

The 12V unit is pretty simple. The Control and Light fuses are connected to 36V Negative, and so these fuses are a good place to connect the DC-DC negative wires. For the 12V light DC-DC I connected negative (black) on the bottom of the light fuse in order to fuse it. The high voltage input (Red) I connected to the bottom (unfused) side of the Lift fuse. The 12V output (Yellow) I connected to wire #12 that used to connect to the battery pack. Mount the DC-DC with a couple small self drilling screws and the lights are all set!

Lift Power

I was not able to find an inexpensive 18V output DC-DC so the Lift DC-DC requires modifications in order to get it to put out 18V instead of 12V. This is a little tricky as you’ll need to open it up and add a 5.1K resistor to the network that sets the output voltage. Fortunately there is an unused pad at R10 for a surface mount resistor. Soldering in a 5.1 K resistor on the empty pad labeled R10 raises the output voltage to about 18.5V. Mine had 25V rated output capacitors so I expect it won’t mind the higher output voltage.

Once the Lift DC-DC was modified I connected the HV input (Red) to the top side of the lift fuse to keep it fused (remove wire #17 from the fuse for later use.) The thicker negative wire (Blue) I combined with wire #51 that used to tap the battery and then connected both wires to the top of the light fuse for a unfused B- connection. Both negative wires (Blue and Black) are connected inside the DC-DC, so I capped the thinner black wire from the DC-DC since it’s unnecessary. The modified now 18V output of the DC-DC (Yellow) I connected to the wire that I removed from the top of the lift fuse, wire #17.

This is the wiring diagram that I used for this E15. I think they are also available somewhere on the web. I’m guessing you already have one if you’ve done a lithium conversion. If yours looks different than mine, beware that the required wiring connections may be different.

I switched the main power switch back on and everything (aside from the intermittent corroded light fuse) is working well and bringing smiles.

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