This thread is a little stale, but I have an application to bring it back to life.
Has anyone designed a solar powered go-kart? There is a high school challenge here sponsored by the local University. This seems like an application that could use a large array with a small battery to keep weight down. I'm considering a 69aH-85aH AGM battery range @ 48V with three SunPower 327W modules wired in series with a Midnite 250 controller. Any advice would be appreciated, especially regarding: - Safety - Monitoring - Maximizing endurance (ties into monitoring) Jason Szumlanski Fafco Solar On Thu, Jul 19, 2012 at 8:02 PM, <toddc...@finestplanet.com> wrote: > what is the point of having battery backup if is is so small as to not > really be able to back anything up (except when the sun is shining)? > > > > this seems like a system design error rather than a charge controller > problem. > > > > my .02 > > > > todd > > > > > > > > > > On Thursday, July 19, 2012 4:35pm, "Brian Teitelbaum" < > bteitelb...@aeesolar.com> said: > > Drake, > > I’ve been hounding a couple of the charge controller manufactures about > this issue, but so far I just haven’t seen a light bulb go off in their > heads, but I’ll keep trying, and maybe this is a better forum to do it. > > MPPT controllers can be adjusted to current limit at amperage values > below their rating, but if you do that, you are also limiting the output of > the array in general, and the amount of PV power available to run the loads > directly from the array (through the inverter). Not the best use of > available PV power. > > Say you have an 80A controller and a 200AH battery. With current > technology, you have two choices: > > Let the controller operate at 80A. If you have loads to draw off some of > the current (or sell to the grid), great, but if not you could be seeing a > charge rate of C/2.5, which would be pretty hard on a sealed 200AH battery, > to say the least. Granted, the battery voltage would rise pretty quickly, > and the controller would start to taper off, but it would still see high > currents especially if the absorption time is set long. Not a happy > scenario. > > Or, you can set the current limiting on the controller to 20A for a C/10 > charge rate. But if you had loads drawing 60A, you would be pulling that > additional 40A from the battery and not using the array’s full power. Also > not a happy scenario. > > What we need is a controller that can read the signal from a shunt at > the battery, and use that as the basis of current limiting control. > > For example, if we have an array that can produce 80A of current, but we > want to limit the battery to 20A of charge, there would be 60A of potential > current there to run loads without drawing on the battery. If there are no > loads running, the controller should current limit at 20A (reading from a > shunt), but if loads are turned on, the controller should be able to let > more current through while still limiting the battery to 20A. When loads > are shut off, the controller should go back to a 20A limit. > > This doesn’t all have to happen very quickly as a battery can take a > heavier charge for a short period of time, but I think that this would be a > major improvement of controller function. > > Of course, if you are grid-tied you can sell all the excess power, but > if the grid goes down, or you are off-grid….? > > Because of the low cost of PV and the high cost of batteries these days, > I’m seeing more and more requests for large arrays with smaller batteries. > I also think that PV is now cheap enough to allow for oversizing of arrays > for better battery charging on cloudy days, which can reduce generator run > times. We need smarter controllers. > > What say ye, charge controller gurus? > > Brian Teitelbaum > > AEE Solar > > *From:* re-wrenches-boun...@lists.re-wrenches.org [mailto: > re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *Drake > *Sent:* Thursday, July 19, 2012 2:21 PM > *To:* RE-wrenches > *Subject:* [RE-wrenches] Small battery bank vs too large array > > > > Hello Wrenches, > > Where can I get a device that will measure current through a shunt and > create a signal to trigger a relay? > > We want to be able to use a 2 kW array with four, 200 AH sealed batteries > on an Outback system. 2 kW of PV would be too much amperage for the > batteries. The idea is to open relays to disengage strings in conditions > of high current to the batteries. > > The reason for this is to create backup systems where power will be > abundantly available when the sun shines. The system will normally connect > to the grid, except during outages. In normal charging conditions the > power will go straight to the grid. When the grid is down, power will be > available for loads and battery charging, but batteries will be protected > from overcharge? > > Any suggestions on ways to accomplish this are welcome! > > Thanks > > Drake > > > Drake Chamberlin > *Athens Electric LLC > OH License 44810 > CO License 3773 > NABCEP Certified Solar PV Installer > 740-448-7328 > *http://athens-electric.com/ > > > > Sent from Finest Planet WebMail. > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@lists.re-wrenches.org > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org > > >
_______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org