Phil,<div>Good explanation of the feature. When did GCC make it into the firmware, and can the older ones be updated? It sounds like a perfect solution for some of my installations.<br><br><div class="gmail_quote">On Fri, Jul 20, 2012 at 12:34 AM, Phil Undercuffler <span dir="ltr"><<a href="mailto:solarphil@gmail.com" target="_blank">solarphil@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">OutBack implemented Global Charge Control in the FM charge controllers<br>
a while back, based on the input of the good folk at SELF who worked<br>
to power a number of hospitals and clinics in Haiti after the<br>
earthquake. In some of those systems, the PV array was based on the<br>
typical running consumption of the hospital, in the 30 - 100 kW if I<br>
remember right, and the battery bank was relatively modest. However,<br>
on the weekends and holidays without the normal AC loads the PV input<br>
was considerably more than the battery could absorb without<br>
destructive heating, something like a C2 or C5 rate.<br>
<br>
Global Charge Control is implemented using the MATE3, a FN-DC and FM<br>
charge controllers set to GT mode. You set a high charge current<br>
limit in the M3, and then it monitors the charge current going to the<br>
batteries. In normal operating mode the controllers stay in wide open<br>
mode, harvesting as much power as possible. However if the loads drop<br>
and the total current from the charging sources begin exceed the<br>
global charge limit, the system compensates and the controllers back<br>
off to prevent sending too much current to the batteries.<br>
<br>
In today's world of PV modules being cheaper than diesel, we're seeing<br>
a lot more systems that can use this tool.<br>
<br>
Hope this helps,<br>
<br>
Phil<br>
<div class="HOEnZb"><div class="h5"><br>
<br>
<br>
On Thu, Jul 19, 2012 at 7:56 PM, <a href="mailto:boB@midnitesolar.com">boB@midnitesolar.com</a><br>
<<a href="mailto:boB@midnitesolar.com">boB@midnitesolar.com</a>> wrote:<br>
><br>
><br>
> I didn't see that Brian T had the same idea until after I sent that email<br>
> off to Allan...<br>
> boB<br>
><br>
><br>
><br>
><br>
><br>
> On 7/19/2012 7:53 PM, Allan Sindelar wrote:<br>
><br>
> Wrenches,<br>
> I forwarded Brian's post on to Robin at Midnite, as I thought it was an<br>
> interesting idea. Below is his response, as well as boB's.<br>
> Allan<br>
><br>
> Allan Sindelar<br>
> <a href="mailto:Allan@positiveenergysolar.com">Allan@positiveenergysolar.com</a><br>
> NABCEP Certified Photovoltaic Installer<br>
> NABCEP Certified Technical Sales Professional<br>
> New Mexico EE98J Journeyman Electrician<br>
> Founder and Chief Technology Officer<br>
> Positive Energy, Inc.<br>
> 3209 Richards Lane (note new address)<br>
> Santa Fe, New Mexico 87507<br>
> <a href="tel:505%20424-1112" value="+15054241112">505 424-1112</a><br>
> <a href="http://www.positiveenergysolar.com" target="_blank">www.positiveenergysolar.com</a><br>
><br>
> Allan, It is simpler than what is being suggested. The reason they want to<br>
> limit to 20 amps is because the battery doesn’t need anymore than that. The<br>
> controller will automatically limit the charge current as the battery gets<br>
> full. If a large load is turned on, the controller will try to refill the<br>
> battery up to its capacity. The 80 amps will quickly be reduced because the<br>
> voltage will rise to the point where the charge tapers off.<br>
><br>
> There is nothing else that needs to be done. If the problem is that the<br>
> battery bank is too small for a big controller, the best answer is to get<br>
> more batteries. A 80 amp charger into a 200 amp hour battery is going to<br>
> raise the battery voltage so quick, it will not affect the battery at all.<br>
> By the way, discharging a battery at 60 or 80 amps is probably going to do<br>
> damage to a small battery also. We do have an input on the Classic that<br>
> could probably be programmed to do as requested. That input feature has yet<br>
> to be implemented. I’m sure we will have discussions about this when the<br>
> time comes to write the input code. Maybe this feature will be designed in,<br>
> but it doesn’t sound like it is a very good feature to spend a bunch of time<br>
> on. After all, the main problem is that the battery bank is just too darned<br>
> small.<br>
><br>
> Bob, Tom and Ryan do you have any comments on the subject?<br>
><br>
> Thanks,<br>
><br>
> Robin<br>
><br>
><br>
><br>
> One idea I had in mind was to have an option, in software, to limit the<br>
> current into the battery,<br>
> when the charging current goes above some set threshold. The controller<br>
> would have to get its information from<br>
> the battery monitor over the network.<br>
><br>
> If it is a grid tie system and grid is there and GT inverter is selling,<br>
> then no problem... The controller<br>
> can work at its full output. If grid or loads go away, then the CC will<br>
> know and it can throttle back at<br>
> that time.<br>
><br>
> We don't have a battery monitor yet, but we will have one. This will be one<br>
> of the settings as well as<br>
> Re-Bulk based on state of charge, ending amps and those types of things.<br>
><br>
> boB<br>
><br>
> On 7/19/2012 8:34 PM, <a href="mailto:maverick@mavericksolar.com">maverick@mavericksolar.com</a> wrote:<br>
><br>
> I say it is waste of time.<br>
><br>
> 1. AGM batteries can take the high current and you are right, the absorb<br>
> voltage is reached and the absorb current is tapered rather quickly. Current<br>
> generation charge controllers are rather fast at the transitions. I have a<br>
> bunch of data from a system with a PentaMetric that shows the battery bank<br>
> going to absorb voltage at grid tie, during cloud events, but only for a few<br>
> seconds at a time.<br>
><br>
> 2. A properly designed GTBB system should cover the connected loads for 24<br>
> hours of each sunny day, at a minimum. Keep in mind, off grid systems are<br>
> designed for that, and 3 days + of backup, etc.<br>
><br>
> 3. I would say, based on my experience, the minimum battery bank should be<br>
> 400Ah. I personally try to set it at 600Ah (48V). It is a backup system<br>
> after all. But the key is the customer's expectations...who are they going<br>
> to call after the lights go out?<br>
><br>
><br>
> Thank you,<br>
><br>
> Maverick<br>
><br>
><br>
> Maverick Brown<br>
> BSEET, NABCEP Certified Solar PV Installer ®<br>
> President & CEO<br>
> Maverick Solar Enterprises, Inc.<br>
> Office: <a href="tel:512-919-4493" value="+15129194493">512-919-4493</a><br>
> Cell: <a href="tel:512-460-9825" value="+15124609825">512-460-9825</a><br>
><br>
> Sent from my HondaJet!<br>
><br>
> On Jul 19, 2012, at 6:35 PM, Brian Teitelbaum <<a href="mailto:bteitelbaum@aeesolar.com">bteitelbaum@aeesolar.com</a>><br>
> wrote:<br>
><br>
> Drake,<br>
><br>
><br>
><br>
> I’ve been hounding a couple of the charge controller manufactures about this<br>
> issue, but so far I just haven’t seen a light bulb go off in their heads,<br>
> but I’ll keep trying, and maybe this is a better forum to do it.<br>
><br>
><br>
><br>
> MPPT controllers can be adjusted to current limit at amperage values below<br>
> their rating, but if you do that, you are also limiting the output of the<br>
> array in general, and the amount of PV power available to run the loads<br>
> directly from the array (through the inverter). Not the best use of<br>
> available PV power.<br>
><br>
><br>
><br>
> Say you have an 80A controller and a 200AH battery. With current technology,<br>
> you have two choices:<br>
><br>
><br>
><br>
> Let the controller operate at 80A. If you have loads to draw off some of the<br>
> current (or sell to the grid), great, but if not you could be seeing a<br>
> charge rate of C/2.5, which would be pretty hard on a sealed 200AH battery,<br>
> to say the least. Granted, the battery voltage would rise pretty quickly,<br>
> and the controller would start to taper off, but it would still see high<br>
> currents especially if the absorption time is set long. Not a happy<br>
> scenario.<br>
><br>
><br>
><br>
> Or, you can set the current limiting on the controller to 20A for a C/10<br>
> charge rate. But if you had loads drawing 60A, you would be pulling that<br>
> additional 40A from the battery and not using the array’s full power. Also<br>
> not a happy scenario.<br>
><br>
><br>
><br>
> What we need is a controller that can read the signal from a shunt at the<br>
> battery, and use that as the basis of current limiting control.<br>
><br>
><br>
><br>
> For example, if we have an array that can produce 80A of current, but we<br>
> want to limit the battery to 20A of charge, there would be 60A of potential<br>
> current there to run loads without drawing on the battery. If there are no<br>
> loads running, the controller should current limit at 20A (reading from a<br>
> shunt), but if loads are turned on, the controller should be able to let<br>
> more current through while still limiting the battery to 20A. When loads are<br>
> shut off, the controller should go back to a 20A limit.<br>
><br>
><br>
><br>
> This doesn’t all have to happen very quickly as a battery can take a heavier<br>
> charge for a short period of time, but I think that this would be a major<br>
> improvement of controller function.<br>
><br>
><br>
><br>
> Of course, if you are grid-tied you can sell all the excess power, but if<br>
> the grid goes down, or you are off-grid….?<br>
><br>
><br>
><br>
> Because of the low cost of PV and the high cost of batteries these days, I’m<br>
> seeing more and more requests for large arrays with smaller batteries. I<br>
> also think that PV is now cheap enough to allow for oversizing of arrays for<br>
> better battery charging on cloudy days, which can reduce generator run<br>
> times. We need smarter controllers.<br>
><br>
><br>
><br>
> What say ye, charge controller gurus?<br>
><br>
><br>
><br>
> Brian Teitelbaum<br>
><br>
> AEE Solar<br>
><br>
><br>
><br>
> From: <a href="mailto:re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a><br>
> [mailto:<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a>] On Behalf Of Drake<br>
> Sent: Thursday, July 19, 2012 2:21 PM<br>
> To: RE-wrenches<br>
> Subject: [RE-wrenches] Small battery bank vs too large array<br>
><br>
><br>
><br>
> Hello Wrenches,<br>
><br>
> Where can I get a device that will measure current through a shunt and<br>
> create a signal to trigger a relay?<br>
><br>
> We want to be able to use a 2 kW array with four, 200 AH sealed batteries on<br>
> an Outback system. 2 kW of PV would be too much amperage for the batteries.<br>
> The idea is to open relays to disengage strings in conditions of high<br>
> current to the batteries.<br>
><br>
> The reason for this is to create backup systems where power will be<br>
> abundantly available when the sun shines. The system will normally connect<br>
> to the grid, except during outages. In normal charging conditions the power<br>
> will go straight to the grid. When the grid is down, power will be<br>
> available for loads and battery charging, but batteries will be protected<br>
> from overcharge?<br>
><br>
> Any suggestions on ways to accomplish this are welcome!<br>
><br>
> Thanks<br>
><br>
> Drake<br>
><br>
><br>
> Drake Chamberlin<br>
> Athens Electric LLC<br>
> OH License 44810<br>
> CO License 3773<br>
> NABCEP Certified Solar PV Installer<br>
> 740-448-7328<br>
> <a href="http://athens-electric.com/" target="_blank">http://athens-electric.com/</a><br>
><br>
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</div></div></blockquote></div><br><br clear="all"><div><br></div>-- <br>Chris Mason<div>President, Comet Systems Ltd</div><div><a href="http://www.cometenergysystems.com" target="_blank">www.cometenergysystems.com</a></div>
<div>Cell: 264.235.5670</div><div>Skype: netconcepts</div><br>
</div>