Hi Gary, Why don't you try to connect the two first and see if there is a problem that you want to solve, instead of first building a solution and then finding out that it is not needed at all? Even at opposite SoC, the difference in voltage between two 12V banks is typically less than 1V. If actively charging one bank (peak up to 15V) then it may rise to 3V at most. I expect that the effect of hooking them in parallel will be underwhelming in terms of excitement. There may be a little spark or small crackle but the difference in voltage would typically not give big inrush currents and at typical less than 1V difference, there will be not much of spark noticeable. If you want to make sure that it is impossible to create big sparks then you can simply connect with a rather thin hookup so it provides a little series resistance - not enough to really affect the balance between the two banks but enough to reduce any inrush to no more than a couple dozen Amps. I don't think you need much circuitry to do this, just select a wire that has more than 0.01 ohms series resistance per wire length you are using and the twin leads will add up in resistance to reduce inrush to below 50A even if there is 1V difference initially. At 5A continuous current the difference between the packs will then beno more than 0.1V Hope this helps,
Cor van de Water Chief Scientist Proxim Wireless office +1 408 383 7626 Skype: cor_van_de_water XoIP +31 87 784 1130 private: cvandewater.info http://www.proxim.com This email message (including any attachments) contains confidential and proprietary information of Proxim Wireless Corporation. If you received this message in error, please delete it and notify the sender. Any unauthorized use, disclosure, distribution, or copying of any part of this message is prohibited. -----Original Message----- From: EV [mailto:[email protected]] On Behalf Of Gary Krysztopik via EV Sent: Monday, June 06, 2016 9:26 AM To: Electric Vehicle Discussion List Subject: Re: [EVDL] Current limiting Thanks guys! I have a bag of in rush current limiters from many years ago that I never used and I like the halogen bulb idea. I have 400ah cells (4.8kwh) in our RV with 1kw solar and another 10kwh in our truck that I want to connect for more capacity. Trying to avoid sparks and melting and all that stuff. Since both are capable of very high current I am not sure what to expect when connecting at opposite SOC. On Jun 5, 2016 10:41 PM, "Mike Nickerson via EV" <[email protected]> wrote: > Hi Lee, > > I don't think that is how in rush current limiters work. I use them to > protect my DC-DC converter caps so they don't get whacked with a high in > rush current when the connection is first made. > > https://en.m.wikipedia.org/wiki/Inrush_current_limiter > > Mike > > On June 5, 2016 10:19:55 PM MDT, Lee Hart via EV <[email protected]> > wrote: > >Mike Nickerson via EV wrote: > >> If the long term current draw will be less than 10A or so, you could > >use an in rush limiting resistor. That is a resistor with a negative > >temperature coefficient. When cool, they have a very high resistance. > >As they heat up, their resistance drops. > > > >This is probably the opposite of the function Gary wants. Inrush > >limiters have a very LOW resistance initially, so the peak current when > > > >you first connect the batteries is very high. As the inrush limiter > >heats up, its resistance rises -- so you wind up with quite a limited > >amount of current between them. > > > >Gary Krysztopik wrote: > >>> Does anyone have any cheap tricks for regularly connecting two large > >12 > >>> vdc packs together (one stationary and one mobile) and limiting > >inrush > >>> current when they are at different SOC? They both have huge current > >>> capability but I need it for energy vs power so one has small wires > >and > >>> fuses. > > > >The "cheap trick" is to connect a light bulb between them. Pick the > >bulb > >so your normal current is well below what the bulb normally draws on > >12v. For example, a #57 brake light draws about an amp, and a headlight > > > >about 4 amps, and a halogen spotlight around 10 amps. > > > >The bulb won't allow more than its normal rated current to flow between > > > >the batteries. If you try, it just lights up. But when the current is > >less than this (such as while on standby), the bulb's resistance is > >LOW. > >The bulb is out, and the two batteries are essentially connected in > >parallel for float charging, etc. > > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > Read EVAngel's EV News at http://evdl.org/evln/ > Please discuss EV drag racing at NEDRA ( > http://groups.yahoo.com/group/NEDRA) > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20160606/f63e da4f/attachment.htm> _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at 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 Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
