Cut T-sense cable - can I repair with solder and heat shrink?

Had something similar happen on my boat build last year — caught the T-sense wire with a Stanley knife when trimming cable ties. Didn't even notice until I powered everything up and the BMS was throwing a temperature fault.

Short answer: yes, solder and heat shrink works fine. Done it myself. The T-sense line is just carrying a low-voltage signal from the NTC thermistor to the BMS, not shifting any real current. A solid solder joint won't affect the resistance in any meaningful way, and the BMS won't know the difference.

A few things worth doing properly though:

• Make sure your solder joint is actually good — cold joints on thin sensor wire are a pain to diagnose later
• Use adhesive-lined heat shrink if you can, especially in a damp environment (very relevant on a boat)
• Keep the repair away from any flex points if possible

I'm running a Daly BMS on Fogstar Drift cells and the T-sense reads perfectly fine after my repair. Checked it against an IR thermometer on a warm charge cycle and it was spot on.

Only caveat I'd add — if your BMS is still under warranty and you're precious about that, document the repair with photos. Some manufacturers can be funny about it.

Anyone else had BMS sensor gremlins they've bodged their way through? Curious whether others have had actual inaccurate readings after a repair, because I've not seen it but it seems theoretically possible if the joint adds significant resistance.

Steve2000 | Posts: 847 | Location: Somerset

@BMS_Geek Yep, totally repairable with solder and heat shrink — done it myself on a Daly BMS after a similar incident. Just make sure you're joining like-for-like on the wire gauge, and use proper rosin-flux solder rather than the cheap stuff.

One thing worth mentioning that people often overlook — once you've heat-shrunk it, give the joint a gentle tug to confirm it's solid before buttoning everything back up. On a boat especially, vibration will find any weakness eventually.

Also double-check your NTC thermistor readings are sensible afterwards (around 10kΩ at 25°C for most common sensors). If your BMS is still throwing temperature faults post-repair, the thermistor itself may have taken damage at the cut point rather than just the wire.

VDH_Boats | Posts: 312 | Location: Array

Done exactly this on my narrowboat build — the T-sense wire is just carrying a low-current signal, so the joint quality matters far more than on a power cable. What I'd add to @Steve2000's point: keep the splice as short as possible and use decent rosin-core solder rather than anything cheap. I made the mistake once of using some no-name stuff and got a slightly resistive joint that was throwing the temperature readings out by a couple of degrees — enough to confuse the Victron BMS into doing odd things. Dual-wall adhesive heat shrink is worth the extra few pence too, especially in a damp bilge environment. Once it's done properly you genuinely won't know it was ever cut.

CopperWelder | Posts: 1,204 | Location: Array

Worth adding a word of caution here — the T-sense wire carries a tiny signal, and a dodgy solder joint won't necessarily kill it outright. It'll just give you slightly wrong temperature readings, which is arguably worse than no readings at all. Your BMS thinks everything's lovely at 22°C while the cells are quietly sulking at 40°C.

Speaking from experience — I bodged a repair on my shepherd's hut build, convinced myself it was fine, then spent three weeks wondering why my Victron kept behaving oddly during charge. Turned out my "perfect" joint had gone high-resistance.

Proper flux, clean wire, good heat shrink with adhesive lining. Don't rush it. And after repair, dunk the whole splice in ice water while watching your BMS temperature readout — if it doesn't drop, your joint's lying to you.

BurnWalker | Posts: 156 | Location: Array

Done this on my narrowboat twice now — once with a knife, once because a cable tie clip chewed through it over a winter. Both times soldered and heat-shrunked, both times fine.

One thing nobody's mentioned: if you're doing this somewhere awkward (and on a narrowboat it's always somewhere awkward), use a proper helping-hands tool or you'll end up with a cold joint guaranteed. Those T-sense wires are thin enough that heat wicks away fast and you'll think you've done a decent join when you haven't.

Also worth labelling the repair with some self-amalgamating tape over the heat shrink so you know where to look if you ever get a fault down the line. Future you will be grateful.

@CopperWelder — what's the actual caution? Post got cut off.