Mike, Sure, having the right tool and a properly researched torque setting is ideal. However, I would like to point out that OEMs often use completely green employees and so giving them a tool and a torque setting is a much more reliable method of ensuring consistency and therefore good QC rather than relying on what each individual considers to be a 'tight' connection. Others with more experience may feel a torque wrench - especially one used improperly - to be more of a hindrance than a help. Hence my question about torque settings.
Regards, Martin. On 7 Jan 2014, at 14:22, Michael Ross wrote: > Martin, > > It is necessary to have a properly sized torque wrench, the willingness to > look up the proper torque setting for the materials involved, and a > willingness to spend the time getting all of the bolts right. The > alternative is you take a chance on shortening the life of an expensive > pack, or running out of power in transit. It is a choice one makes not > torquing well. > > Lot's of people think torquing is trivial. That would not be true of OEM > auto manufacturers. If one does not take their lead... If people don't > obtain the tool, look the torque up, and do it right, then they will either > under or over torque (I am shrugging, but not unsympathetic). I can't > really worry about all the people who strip out threads - I did a fair > amount of that myself before deciding to do it right. > > If a DIY EVr does strip some out we can help them retap or helicoil the > holes. It does happen. > > Here is a reference > > http://bit.ly/1dsHSCw > > Mike > > > > On Tue, Jan 7, 2014 at 5:01 AM, Martin WINLOW <[email protected]> wrote: > >> 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)
