Paul Wallace wrote:
Lee, very strange circuit topology for the implementation of the DC/DC in the USElectricar with the Datel DC/DC. The DC/DC input has a fuse added, that looks good. The output, however, is very strange. the common output pin of the DC/DC goes directly to the Emeter negative lead. The positive DC/DC output pin is routed through a diode, and then two 5.1ohm resistors in parallel (2.55ohms) and finally to the positive input of the emeter. There is also a 1000uf 16vdc electrolytic cap on the output. No wonder I see such odd input voltage to the emeter when it is drawing current. The diode drop alone is at least 0.6v.
It sounds like US Electricar added the "EV filter" circuit shown below as an external circuit. Most E-meters already have this circuit internally, so it isn't necessary to add another one externally.
The early E-meters did not have this circuit. They were prone to reset if the supply voltage dipped for even a few milliseconds.
The specs say the minimum input voltage is 10v. However, adding the filter obviously adds a diode drop, so 10.6v is a more practical minimum. If US Electricar added another diode, then the minimum is around 11.2v. That's getting pretty high. I can easily see a car's 12v supply drop below this when you turn on some high-current device (headlights, heater blower motor, etc.)
I used a 12v-to-24v DC/DC with my Companion. This provides a lot more drop-out margin. Since the E-meter's internal supply is a switcher, it draws about half the current at twice the voltage, which also helps.
It may, or may not have the EV filter inside. Physically, the filter is a 1000uF 35vdc electrolytic capacitor across the Link-10's power input, plus a 1N4001 diode and 3.3 ohm resistor in series. Bad ASCII schematic (view with fixed width font like Courier). +12v power____|\|____/\/\________+12v power to Link-10 from DC/DC |/| 3.3ohm | 1N4001 resistor _|_+ diode ___ 1000uF 35vdc capacitor common________________________|__common (NOT ground!)
-- The main goal is not to complicate the already difficult life of the consumer. -- Raymond Loewy (considered the father of industrial design) -- Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.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)
