The reason people use charge controllers is mainly to stop overcharge. The secondary benefit with a controller that can do boost or buck is MPPT (Maximum Power Point Tracking), so you can couple the PV to the battery more effectively and waste less of the energy as heat. If you hook ten 120W 12 volt panels (~ 10 amps each) in parallel with your 12 volt battery, you would get (theoretically) 100 amps in. If you hook those same panels up in series, you would get 12 volts out at 10 amps. The voltage stays at 12v when hooked to the battery, not the ~120v it would be open-circuit. The ideal voltage the panels "want" to operate at depends on several factors, and a well-engineered MPPT controller can let the PV panels operate in their ideal voltage range for any given condition, while letting the battery voltage be what it is going to be. This changes throughout the day, and can also be different every day as sun angles and temperatures, change and PV panels age.
I recommend configuring your array for a voltage higher than your pack, and then use an MPPT controller to buck down to the pack's voltage, without the need for pack reconfiguration. The idea you have about contactors will likely not work without using a separate BMS for each sub-pack segment. There are few off-the-shelf BMS' that will allow this kind of re-configuration safely. We use a custom-engineered MPPT boost controller on our vans ( https://maxwellvehicles.com/). It takes 4 panels at about 150 volts total and uses an MPPT algorithm to boost the PV voltage to the pack voltage (~375v). This is another way to do it, but we couldn't find anything off-the-shelf so we built it ourselves. (Picture Link: https://ingineerix.com/pic/?maxwell-epro-solar-mppt ) On Sat, Jan 13, 2024 at 8:43 AM paul dove via EV <ev@lists.evdl.org> wrote: > Hey John, > You say you run your shop off of the 24v setup….. do you have an inverter > that makes 120VAC? Or 240VAC? > Seems to me that all you need is an inverter and a charger. There would be > some losses but simple to implement. > If you go straight to the battery from the array you could use a DC to DC > converter. Not sure of availability at those voltages. Let me think a bit > and I’ll back to you. > Paul > > > Sent from AT&T Yahoo Mail for iPhone > > > On Friday, January 12, 2024, 9:21 PM, John McIntire via EV < > ev@lists.evdl.org> wrote: > > Having read this list for several years now, and commented occasionally, I > know there some electrical engineers out there. It is to you I address this > problem. > > I am now the proud owner of a '96 Solectria Force which will be receiving > a new battery made up of 48, 280A LiFePo4 prismatic cells. The Force was > designed to run at 156v (13 lead acid batteries). My primary power source > is a 16 panel, 8.5 Kw PV array. Max voltage under load is 43v/panel at 13A. > There is no back up power as I am not grid tied. I do have a small domestic > 24v Li battery to run my shop. The Force battery will be equipped with a > robust BMS. > > I can configure the panels to provide 172v at 52A in full sun but I know > that the voltage and amp will be unstable which does not promote longevity > in Li cells. Normal circumstances have a charge controller between the > battery and the array to even out the voltage. Normal charge controllers > are 48v or less. I would like to find or build a buck/boost circuit that > would match the battery. > > I think I could break the Force battery into 3, 16s packs, charge them > parallel at 48v+ and then reconnect in series for discharge. I think 2 > contactors per pack along with appropriate safety devices would do the job > but that seems cumbersome at best if workable. > > I am not an engineer. I do have 30 years experience with automotive > electronics. Since partial retirement, over the past 15 years I have > converted an S-10 and 2 tractors to run as EVs. So I am somewhat familiar > with the concepts and pitfalls. > > I would appreciate your thoughts and suggestions. Thanks in advance. > > John M > > "Money doesn't talk, it swears"--Bob Dylan > _______________________________________________ > Address messages to ev@lists.evdl.org > No other addresses in TO and CC fields > HELP: http://www.evdl.org/help/ > > > > > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: < > http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20240113/c226d4e6/attachment.htm > > > _______________________________________________ > Address messages to ev@lists.evdl.org > No other addresses in TO and CC fields > HELP: http://www.evdl.org/help/ > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20240114/3a4e6d59/attachment.htm> _______________________________________________ Address messages to ev@lists.evdl.org No other addresses in TO and CC fields HELP: http://www.evdl.org/help/
