Hi: I'm enjoying learning many new ways of looking at things and of practical solutions on this forum. In that spirit, the only thing I would add to this discussion is that the power factor as seen by the AC source will be very poor. In that regard, the larger the caps, the more stable the "DC" voltage, but the poorer the PF.
This will show up as much lower charging efficiency due to the way in which AC current is drawn by the bridge rectifier/capacitor circuit. Here's an actual graph of how a bridge rectifier connected to a capacitor draws AC current, The graph is from my past life a couple of decades ago back when I was studying. It's not a conventional phase-shift PF problem, but rather a form factor PF problem. It shows the current drawn by a 13" PC monitor of that era, before PF correction was mandated for all new products. In this example the 'crest factor', (peak current as measured versus what it could have been if the current was drawn throughout the AC pulses, was about 4x). Depending on the size of capacitor, it can be as high as 7x. The practical effect on the wires and devices including the diodes and charge controller, is that a lot of heat is generated in their power components. The source of the energy for that heat is the AC source and in cases where the AC source is a generator that translates to much higher fuel consumption, (in some cases over 30% more). Out of my tests back then, I also discovered one practical recommendation. If you are using bridge rectifiers connected to capacitors, do not have any length of wire and in particular no loop area in the wires between the bridge rectifier and capacitors. Having wire/loop area introduces inductance into the circuit which behaves somewhat like an ignition coil due to the high speed reverse recovery period of the diodes; and this happens four times every AC cycle. Given the right conditions the voltage spikes caused by that inductance/ignition coil like effect will make short work of the diodes and other components which are on the circuit. The voltage spikes wont be a problem if the bridge rectifier is as close as possible to the capacitors, but due to reverse recovery effect, you'll still be stressing the parts and heating wires. In my opinion, its ok to do this, but I wouldn't push power levels to anywhere near the limits of components and devices. JARMO _____________________________________________________________________________________ Jarmo Venalainen | Schneider Electric | Solar Business | CANADA | Training & Development Specialist - Senior Phone: +604-422-2528 | Fax: +604-420-1591 | Mobile: +604-505-0291 Email: jarmo.venalai...@schneider-electric.com | Site: www.SEsolar.com | Address: 3700 Gilmore Way, Burnaby, BC V5G4M1 *** Please consider the environment before printing this e-mail From: "b...@midnitesolar.com" <b...@midnitesolar.com> To: RE-wrenches <re-wrenches@lists.re-wrenches.org>, Date: 12/16/2014 11:16 AM Subject: Re: [RE-wrenches] Programmable Battery Charger Sent by: "RE-wrenches" <re-wrenches-boun...@lists.re-wrenches.org> Larry, Pitfalls ? The biggest pitfall I would say is if you have a VERY stiff grid. If your Voc is say, 170V DC and the CC current limits it output at say, 169 V DC, they you are going to need to add an input power resistor of a couple Ohms to help cushion the input to be more like a PV module. A lot of times, the grid is not nearly this bad, especially generators. Also, If you are going to do this, I would NOT use Solar mode but instead try Hydro mode set to Manual MPP voltage. First start the MPPV at something just less than Voc or maybe, say, 160 VDC. Then, from main STATUS screen, you can adjust the input voltage up and down by pressing the Soft-Right or Soft-Left keys respectfully. (upper right and upper left keys). Then you can manually get a feel for what it should be set for. The Classic 200 is the only CC of ours that I would use. The 250 would work but the 200 is much more suited. I wish there were a real charger that one could buy that was isolated, and we have never really advocated MPPT charge controllers for this but in a pinch, they always seem to work find. Never did add a "DT" mode (after Daryl Thayer of course), but this hydro mode seems to work OK. If you want to let it sweep but setting it to 3 minutes (or higher) that will also work. If you do that, set the minimum input voltage. Something like 140V or so will keep it from dropping the input voltage too low and either bogging down the input source and the rectifier bridge (especially generators) You can also set the INPUT current limit in the LIMITS menu. This was for hydro in particular. Either limit can help reduce Isc or bogging down issues. The other pitfall is that it is NOT galvanically isolated so you should be very careful. We use an X240 equivalent transformer to keep the batteries going in our burn in rack using 2 Classic 200s and it works great. Also, use a nice and strong full bridge rectifier so that it applies 120 Hz instead of 60 Hz to the input. That is much easier on the input capacitors and things and just makes it work smoother. There are input capacitors (filtering) on most charge controllers. Again, in a pinch this seems to work but watch that input max power point voltage to make sure it is not too high compared to the Voc. If there isn't enough voltage spacing between the two (stiff AC source) then the control isn't going to be very smooth and might risk letting the smoke out. What ever you do here, be very careful what you touch ! boB On 12/16/2014 6:39 AM, Larry wrote: I must have missed the prior discussion about using PV CC. The concept sounds good but how many of you have done this and are there any pitfalls to be aware of? If I use a 20 amp bridge I should be able to produce 80 amps @ 14.4V. For continuous operation, will I need a large heat sink on it? How does the unfiltered full wave peak voltage affect the CC over time? Are they (specifically Midnite) really designed to handle input waveform like this? I like this idea, especially if I can stack the controllers. Thank you, Larry On 12/15/14 6:51 PM, jay peltz wrote: Hi Kirk, If you use a 200vdc midnight CC you'll have no issues. When you rectify 120vac its up around 166vdc ( uses the peak vac which is around 170vac.) For a 150vdc max controller ( midnite 150) or a 144vdc ( outback FM) then a buck transformer or standard transformer is the trick to reduce the AC and hence the DC for these lower voltage units. jay peltz power On Dec 15, 2014, at 5:38 PM, Kirk Herander wrote: This has been discussed on this list in years past. It is possible to use an outback charge controller as a battery charger. You need to put the 120 AC into a bridge rectifier, then feed the 120 DC into the controller’s PV input. So you’ll have an 80 amp battery charger. Kirk Herander VT Solar, LLC Proven PV provider since 1991 www.vermontsolarnow.com dba Vermont Solar Engineering NABCEPTM Inaugural Certificant VT RE Incentive Program Partner 802.863.1202 From: RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Dan Tittmann Sent: Monday, December 15, 2014 8:18 PM To: i...@windsine.org; RE-wrenches Subject: Re: [RE-wrenches] Programmable Battery Charger You can manually adjust Iotas with tweaking the potentiomiters while monitoring it with a god volt meter. But no time adjustment. Daniel Daniel Tittmann CTO Greenwired www.greenwired.com dan...@greenwired.com 707-923-2001 (office) 707-206-5088 (Cell) On Mon, Dec 15, 2014 at 4:21 PM, Windsine Inc. <winds...@gmail.com> wrote: Check out Argus Technologies. RoyR On Dec 15, 2014 4:01 PM, "Larry" <la...@starlightsolar.com> wrote: Wrenches, Does anyone know of a 120/12 volt battery charger that can be programmed for absorb and float voltage and time in absorb mode? I have been needing this product for many years but I can only find it in inverters with built in chargers from Magnum, Outback, and Xantrex. -- Thank you, Larry Crutcher Starlight Solar Power Systems ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. ______________________________________________________________________ _______________________________________________ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
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