Steve, Since it is only 12 or 36V, you could easily find a MOSFET that can do the work of the contactor and draw zero current, it just needs its Gate input to be held at the correct voltage to enable it. Presuming that you are not drawing hundreds of Amps?
Another alternative is a sense resistor that allows the contactor to drop out as soon as there is no current draw and re-enable the contactor when there is current draw again. But that could mean that there are voltage drops while the contactor switches. Another alternative is a latching relay, which does need a pulse to switch state, but no power to either stay on or off. Many choices... Success! Cor van de Water Chief Scientist Proxim Wireless Corporation http://www.proxim.com Email: cwa...@proxim.com Private: http://www.cvandewater.info Skype: cor_van_de_water Tel: +1 408 383 7626 -----Original Message----- From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Steve Clunn via EV Sent: Tuesday, September 16, 2014 7:32 AM To: firstname.lastname@example.org Subject: [EVDL] 4 to 12 Cell Lithium BMS I am working on some Golf Carts and portable 12V power packs that get used sporadically and may sit for months without use. I have contactor on one 12V and 36V that draws about 1 amp. The problem is, if everything is happy, the Mini BMS Circuit keeps the contactor ON. Which draws enough current, that at some point, will drain the battery down. I am trying to come up with a way that the owner can walk away from this system, and come back to it and have it ready to go without having to switch switches OFF and ON. One thought I have had is to set it up with a transistor that controls the contactor. And after so many hours, will turn OFF the contactor. My thought was a Mosfet with a large Capacitor and a Momentary switch to charge the capacitor which would keep the contactor ON for maybe 10 hours while the Capacitor slowly drained down. Of course, the operator will have to engage this each time he uses the battery, but at least it will turn its self off automatically. I am wondering if anyone has any other ideas... that doesn't involve a micro processor. I am noticing that the smaller the parts that I am working on....the longer it seems to take ! -- Steve Clunn Merging the best of the past with the best of the future. www.Greenshedconversions.com -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20140916/31d8 90b6/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) _______________________________________________ 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)