I agree, it seems like maybe 1v difference should be no big deal but one pack has big cable and fuses and the other has small wire and fuses so I didn't want to pop them all. Oh well, you talked me into it - let's see what happens. On Jun 6, 2016 2:34 PM, "Cor van de Water via EV" <ev@lists.evdl.org> wrote:
> 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:ev-boun...@lists.evdl.org] 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" <ev@lists.evdl.org> > 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 <ev@lists.evdl.org> > > 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) > > -------------- next part -------------- An HTML attachment was scrubbed... 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