Dan, The speed of charging will indeed be very dependent on the difference between the state of charge of the two packs and if you want to transfer more energy than half the capacity that is in the solar bank, you will not be able to do that by simply wiring them together, as the packs will tend to go to the same state of charge and also it will take a long time once the charge levels start to get close to each other. It is simple to improve this and no big converters are needed, since all you need to do is to increase the input voltage a little bit. For example, I have these "half-brick" (about 3x3") DC/DC converter modules that take as input 48V nominal (36-75V allowed) and deliver 5V 30A. Just one such a module wired to the solar battery can be added in series with the solar bank voltage to boost it from 48 to 53V which will allow the boat's pack to charge quickly (up to 30A when using 1 module, up to 60A when using 2 of them in parallel)
This means that your boat can be charged to 80% in about 3 hours (or 1.5 hours if you use 2 modules) even if the solar bank voltage is lower than the boat's pack charging voltage, due to the boost. The efficiency is still around 90% since you boost the power up by about 10% (5V on a 50V pack) and consequently the output current is 90% of the input current (the DC/DC converter consumes about 10% of the charging current to provide the 5V boost). Hope this clarifies and gives some ideas. Let me know if you are interested in getting a module. Note that I have two versions of this same 150W module: one has 5V output, the other 15V output and both can be trimmed up/down, so you can use such a module also so provide 12V for lights and accessories powered from a 48V pack. Success, Cor van de Water Chief Scientist Proxim Wireless Corporation http://www.proxim.com Email: [email protected] Private: http://www.cvandewater.com Skype: cor_van_de_water XoIP: +31877841130 Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203 -----Original Message----- From: [email protected] on behalf of Dan Baker Sent: Sun 4/20/2014 6:13 AM To: Electric Vehicle Discussion List Subject: Re: [EVDL] Charging your EV pack from other batteries? Thank you Bruce, Dennis, Willie and Marco for the info. So it sounds like a charge from batteries of similar voltage could work, although the charge wouldn't be very robust/complete depending on the difference in state of charge between the packs? I expect the best charge would be if the solar pack is fully charged and the PV array is under full sunlight conditions and the least would be at night and both packs have been partially drained? Like most leisure craft my boats spend most of the time parked at dock so I would expect the EV pack would likely be connected under the PV pack being charged most of the time. Dump charging or high speed charging really isn't necessary for my use but a quicker than the normal 6-10 hour charge would be nice. I guess I could also use an invertor to convert the 48 volts to 120 volts and plug in my regular wall charger to have a complete charge (cheaply make a high amp step up circuit like Marco suggested) but that sounds much more terribly inefficient. :-( Cheers Dan On Sat, Apr 19, 2014 at 10:41 PM, Bruce EVangel Parmenter < [email protected]> wrote: > I have seen drivers charge their pack from another pack. > > The first instance was when I heard of a couple in the East SF Bay EAA > Chapter, the Cornell's, who both drove EVs. Talk about getting the most > out of the $ they spent on a pack, when a pack was replaced because its > range did not suit their needs, the batteries that still had life in > them were stored in the garage, and kept charged from the solar array on > their roof (this was at a time when there were no solar incentives, and > the Cornell's were way ahead of everyone else. Their roof solar would be > thought of as common place by today's standards). > > When one of them got home, they would recharge their EV off the older > pack which had been recharged from solar electrons. The current they > used to recharge their pack was low, so I would not call it a dump > charge. At that time, a dump charge was what the racers were doing at > the track with high currents (like level-3 power), to get back out to > race on the track (APS racing). > > The other experience was at high current levels, so you could call it a > dump charge of sorts. In both cases, the effort to transfer the power > from one pack to the other was a manual one, where the human brain was > the smart charger. They each used a source pack that was at an > incrementally higher voltage (higher than a destination pack voltage). > > The example is when I hung out with John Wayland at a Sacramento Raceway > nedra.com EVent. His White Zombie at the time I believe had the smaller > Jonson Controls agms. His older pack that used to be in his EV were made > up of Optima yellow top agms. When he came in to his pit location after > doing his run, he would measure his pack voltage, and match that plus > one more 12V agm. Then connect the slightly higher voltage old pack to > his EV's partially spent pack. As the dump current decreased, he would > add another 12 agm to bump up the current. He knew from experience when > to do this so as to not push too much dump current, and to not waste > time on a lower, slower dump current. > > When John's EV pack had reached the finishing voltage, he pushed/goosed > it a little, forcing a higher than normal finishing current into his > EV's pack. This caused his EV's agm pack to steam some of the > electrolyte. John said he did this on purpose because his hot pack > performed better (one could like that thinking: prematurely > aging/destroying his EV's agm pack just so he can get a better race > time, to what the ice heads to when they push their ice beyond > red-line). After he left to go get in line to race again, he had a > genset pushing power into the old Optima set of batteries that was in > his support vehicle. > > I've heard of drivers of today using a controller to push the power from > one pack to another. IT still would require a human to incrementally > bump the current up as the pack charged, but no batteries had to be > added, you could start out by using the highest source pack voltage. > > > {brucedp.150m.com} > > > > - > On Sat, Apr 19, 2014, at 02:12 PM, Dan Baker wrote: > > Hello fellow Evlist users, > > I have question around charging the battery pack on an EV from a larger > > pack of batteries, same voltage. I'm looking to build a stationary solar > > array (48v) and charging 12 x 12 volt 133 amp/hr sealed lead acid > > batteries, 4 batteries per bank These are retired but gently used UPS > > batteries and I will have about 1200 watts in solar going into a > > Morningstar 45 amp solar controller. I would like to be able to charge > > my > > EV boat pack (http://www.evalbum.com/4767) from this pack, UPS batteries > > again, but 4 x 12 volt AGM 133 amp/hr. > > My questions for the list: how do I transfer the charge from the solar > > bank to the EV pack? Can I just use a charge cable directly and the two > > banks will equalize? Or would I need to use a charge controller? I > > have > > another 45 amp solar controller I could hook from the main battery pack > > to > > the EV pack but I fear the input amps would exceed it? I remember a > > while > > back someone mentioned they were charging a lawnmower from a truck pack, > > wish I could find more info on this ... > - > > -- > http://www.fastmail.fm - Or how I learned to stop worrying and > love email again > > _______________________________________________ > 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) > > -------------- next part -------------- An HTML attachment was scrubbed... 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