Because the resistance of copper changes 4% for every 10 degree change in temperature.
Manganin, which shunts are made of, barely change at all. Typically it's less than 0.05% in the normal temperature range and 0% around 30-40C. Here's a graph http://images.elektroda.net/89_1304228034.png Copper would be a vertical line on the same scale as that graph. So if you want anything more than a rough indicator, a battery link is woefully inadequate. On Wed, May 14, 2014 at 11:11 AM, Jan Steinman via EV <[email protected]>wrote: > > From: Michael K Johnson via EV <[email protected]> > > > > That AH meter at lightobject looks very interesting. It doesn't say > > what shunt or range of shunts it can use that I can see. > > > > I have a buck converter that I can put on my tractor to power the > > meter, but obviously I'd need to use a shunt to measure current. I > > have a 50mV/500A shunt installed; do you have docs to check whether it > > would work? > > My favourite shunt is the longest battery lead. :-) Why drop any more > voltage than you already are dropping? > > But you need a system that can be calibrated. If your longest lead drops > at least 50 mV, you can put a trimpot across it to bring it down to exactly > 50 mV. I've done this on two different "house battery" systems for campers, > and it worked well. I put an "amp clamp" meter on the cable, together with > a constant load (turning all the lights on in the camper works well), then > trimming the pot until the readings were the same. > > Jan > > > On Wed, May 14, 2014 at 12:21 AM, John Lussmyer via EV > > <[email protected]> wrote: > >> On Tue May 13 21:11:33 PDT 2014 [email protected] said: > >>> Thanks, Denis. > >>> > >>> It looks like a pretty simple display. I'm sorta hoping for something > with more numbers on it. There seem to be a number of units on eBay that > only go to 100 V and 30 A: > >>> > http://www.ebay.ca/itm/5-in-1-Digital-Combo-Panel-Meter-DC100V30A-Volt-Amp-kWh-Watt-Working-Time-/181403417248?pt=LH_DefaultDomain_2&hash=item2a3c7c7aa0&_uhb=1 > >>> > >>> but I'm hoping for something more like this that will do 196V and up > to 500 A: > >>> http://www.accuenergy.com/?discography=acudc-240-series > >>> > >>> This unit could display volts, amps, and kWH simultaneously, but I > haven't found a supplier nor even a price! > >> > >> I'm going to try one of these: > >> > http://www.lightobject.com/Programmable-Digital-AH-meter-Ideal-for-battery-monitoring-P278.aspx > >> > >> I have it on my desk, but haven't hooked it up to anything yet. > >> > >> > >> -- > >> > >> Try my Sensible Email package! > https://sourceforge.net/projects/sensibleemail/ > >> _______________________________________________ > >> 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) > >> > > > > :::: It is only the great men who are truly obscene. If they had notdared > to be obscene, they could never have dared to be great. -- Havelock Ellis > :::: Jan Steinman, EcoReality Co-op :::: > > _______________________________________________ > 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) > > -- www.electric-lemon.com -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20140514/939040e9/attachment.htm> _______________________________________________ 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)
