I'm slightly concerned that without qualification, inexperienced DIY EVrs will start over-torquing there connections. Obviously, different size bots will require different torques. When I bought my Thundersky cells in 2008, I could not get a sensible answer out of them about what torque to use for the bots (8mm in that case). Anyone care to offer a rule of thumb for the usual 6mm and 8mm bolts used with most LiFePo4 cells? MW
On 6 Jan 2014, at 14:22, Michael Ross wrote: > I recently took apart a nice little OEM battery pack and every terminal on > it was barely hand tight. I reassembled with SS socket head screws instead > of the Phillips screws, and torqued the 5mm bolts to spec. All you need to > do is torque them right and they will not loosen. Do not use lock washers > as they compromise the clamping force. If you look at bolted joints on high > quality equipment you will find properly designed joints with no > lubrication or thread-locker - they just torque the right. I worked for > Caterpillar and can vouch for their practices - needed to survive the worst > vibration environments imaginable. My Toyota cars over the last 30 years > are all produced this way. I don't use conductive grease, I just go with > clean and tight. > > For reference: > > 1 N m = 8.8in lb = 0.74bft lb > > I tightened the 5's to 35 in lb (4 Nm). > > Unfortunately, there are a lot of units for measuring torque. Inch pounds > are best for the small wrenches we have in the US. > > My joints were the terminals of 32120 cells, SS M5 screws, with nickel > plated copper straps, and stainless steel flat washers (lock washers thrown > away). I am not sure what the terminal with the tapped threads is made > from. It is s tamped and formed part, maybe SS, but could be a plated > brass or copper... > > On Mon, Jan 6, 2014 at 7:26 AM, Mark Hanson <[email protected]>wrote: > >> Hi Folk's, >> last night a overvoltage battery balancer #22 shut down the charger at >> 4.0V. At first I thought it was a bad OV balancer detector but after >> replacing the circuit it still did it so I put a scope across the battery >> cell and noticed the charging pulsed waveform going from 3.3V to 4.0V 60 hz >> when adjacent cells were fairly solid (signifying a high impedance >> condition). I thought I had a bad cell but after sanding under the copper >> strap & adding 3M dielectric grease & torquing back down, it charged >> perfectly with no faults, back to low impedance. I found a few other >> battery terminal bolts not tight after 20k miles (even with sealing paint >> on terminal bolts CALB 130). So it's best to tighten terminal bolts on >> lithiums every 10k miles it seams. I used to tighten terminal bolts on old >> lead GC batteries every 500 miles but didn't think it was necessary with >> lithiums but apparently they need it as well just less often. >> Best Regards,mark _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
