On 25 Jul 2015 at 6:20, damon henry via EV wrote: > this is the first time I have ever heard of using a zener diode as a > method to create an isolated power supply for [an e-meter]. Is it > really that simple?
I guesss it depends on what you mean by "isolated." The E-meter, at least the original one, doesn't have to be isolated from the traction battery. In fact on page 50 of the old Cruising Equipment E-meter manual I see a mention of using a 24v tap on the traction battery to power the meter. http://www.evdl.org/docs/ce-emeter.pdf Maybe the isolation of concern here is keeping the traction battery isolated from ground. If you used the EV's house battery to power the E-meter, you'd have to either ground the neg of the traction pack, or float the 12v battery's negative (which would be pretty tough to implement). A 12v input DC:DC converter (which you could buy from CE though I'm sure it wasn't cheap) between the house battery and the E-meter took care of the problem. The other reason to use a DC:DC was to prevent unbalancing your EV battery with a 24v tap. On 25 Jul 2015 at 10:50, Robert Bruninga via EV wrote: > The disadvantage of any zener power supply/regulator is that you are > wasting all the drop-down voltage as heat. Is it really enough to be concerned about? Powering the E-meter takes 28 to 150ma, depending on display state. Unless my math is wrong, if you have a 48v battery and burn off 24v of it in a zener or regulator chip, you're wasting between 0.67 and 3.6 Watts. That's less than the power used by an incandescent night light. David Roden - Akron, Ohio, USA EVDL Administrator = = = = = = = = = = = = = = = = = = = = = = = = = = = = = EVDL Information: http://www.evdl.org/help/ = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Note: mail sent to "evpost" and "etpost" addresses will not reach me. To send a private message, please obtain my email address from the webpage http://www.evdl.org/help/ . = = = = = = = = = = = = = = = = = = = = = = = = = = = = = _______________________________________________ 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)
