Torqeedo 1003/1103 battery hack question - Page 1
Forum section: electronics / projects

author: RoG
author_rank: Newbie
timestamp: July 03, 2025, 06:19:39 pm
content: I have a older Torqeedo 1003 with a 400 watt-hr battery and a newer 1103 with a 920 watt-hr battery.I was playing around today with the old one, thinking perhaps it could be possible to modify that small, near useless battery such that it could be powered by a external source, perhaps two LiFePO4 12V in series (about 26.8V fully charged) or if that did not work, then maybe a DC-DC that output closer to the fully charged 32.7V of the original batteries. I know there are a few who have made their own controller using an arduino or something similar, but I was thinking it would be cool to have the original battery case and tiller arm such that you could either use the 920 watt-hr unmodified battery as originally intended, or swap in this now empty 400 watt-hr battery case that still allows the tiller connection but has external leads to whatever external battery bank you have. Possibly put the DC-DC (if it won't run on 26V) inside the old 400 watt-hr battery case. Nice and clean.First test I did was disconnect the battery +/- from the BMS and also the 12 pin balancing lead connector. I then connected (fused of course) power leads to the BMS from my 26.8V bank and plugged in the tiller (the bms and tiller connections are in the top part of the 400 watt-hr battery box). Nothing happens when the power button is pressed. Checking back, I plugged in the old battery leads, giving the BMS the higher 32.7V it might expect, and still nothing happened. It was only after plugging back in the balancing leads that pressing the power button on the tiller caused the display to light up.Ok, so I measured the balancing leads, and rounding, it was something like 0V,4V,8V,12V,16V,20V,24V,28V,32V,0.2V,0.2V. 11 wires used. I think the last two, which are black, are actually a thermal sensor of some type, which makes sense. I have not traced them to the sensor to confirm, but it is a good guess.Anyway, so now I am thinking that in order for the BMS to think everything is ok and accept commands from the tiller arm, I will need to supply some fake balancing voltages.Now here is the question. Should I try a resister divider ladder to generate the fake voltages. I sort of assume the BMS doesn't draw/supply much current through these leads at least when not in charging mode (which I would never be in). If it is just reading the voltages into some sort of high impedance ADC, might a moderately stiff divider be a simple way of tricking it? Also there could be a slight possibility it is not coming on because it doesn't see the thermal sensor...I could try to disconnect that separately to see if it is a requirement.Any ideas?

author: RoG
author_rank: Newbie
timestamp: July 03, 2025, 10:41:38 pm
content: Hah, so I tried just supplying the ground and 8S pin on the balancer, along with the ground and positive +26V from my external battery to see if the other balancer pins were needed. The 8S pin having a thicker trace and leading to a voltage regulator makes it look like the BMS board electronics are powered off the balancer lead input.After a few seconds...zzzzzsssnap, and the onboard 25 amp fuse blows. I was....whut? There is nothing connected, no motor or anything.Well, inspecting the board, there is a big fat jumper wire that goes from the main battery positive input to a IRF2804S-7P which is a 160 amp mosfet. It seems this mosfet can connect the battery+ and battery- together, blowing the main board fuse.I guess the onboard electronics of the BMS see 26V on the last pin of the balancer and go "oh crap", activating that mosfet and blowing the main board fuse, which has the effect of isolating the battery. Is this a normal thing?

author: RoG
author_rank: Newbie
timestamp: July 04, 2025, 12:50:34 am
content: It works! I replaced the 25 amp fuse and built a little resistor divider board using eight 10k resistors to trick the BMS. I also added a 32k resistor across the thermister line. Powered it up again with my two LiFePO4 12V batteries (26.8V+ charged) and it came alive no problem and no fuse blow. Hooked up the outboard motor and it seems to operate quite well (out of water so no load but the top end speed seemed reasonably close to the factory battery).A wide range DC-DC would be a little nicer and there is a lot of room in the battery case for one, but I can't seem to find something that is 24V to 60V input and output around 30V at 40 amps.