Has anyone besides me thought about delaying the start time of pv charging? After learning recently that my batteries like a lot of amps I realized that most days the batteries are already into absorb by the time my panel sees the best sun. I was thinking I could fool theClassic into turning on later by changing the time or longitude setting but I really don't want to play around with my settings. It might be a nice feature to have a delayed start time that you could turn on and off. Maybe others have already thought of this or maybe it's just a bad idea but I thought it would be nice to hit my batteries with max. current from time to time. I'm sure most people don't want to lose any available watts but most of the time I've got excess power since I'm not home to use it so I just thought I would throw it out there.
Quote from: Wxboy on April 15, 2012, 11:16:54 PM
Has anyone besides me thought about delaying the start time of pv charging? After learning recently that my batteries like a lot of amps I realized that most days the batteries are already into absorb by the time my panel sees the best sun.
I've thought about it, but for different reasons. On most sunny days I am in float before noon.
Sometimes I plan to use shop tools in late morning. If I am already in late absorb or float, the energy use of the tools could pull me back down to bulk stage again. That may constitute another battery charge cycle (of which there are a finite number).
I've been advised to use the tools while still in the bulk stage of charging. On a sunny day if I delay the charging until an hour or so before I use my tools, I will still reach float that day.
--vtMaps
I am a fan of having the delayed charge capability in the CC, to maximize I Charge, and to allow a nominal 15% DOD, by delaying any charge for a few days. The multi day charge delay would probably require the addition of a Low Voltage setpoint which would also initiate the charge cycle.
Both of the above can be done manually. But have several systems that I manage, and would be nice to have this done automatically, as it is a bit inconvenient being several places at once.
Realize that there ARE limits on just how much charge system control that a CC can take on, and on systems with multiple CCs, the control would need to be communitated twix them. It is possible that a Battery Monitor/Charge Manager box would be the preferred location of these additional control functions ... BUT, the mind does wander.
These functions can be done externally to the CC, by switching the PV input to OFF with a SS Relay, for example. But, given the currents that can be involved, and small efficiency loss, would like to see the CC do the switching function.
Altho, higher on my list of wants is for Networked Classics sharing the charge functions.
Vic
I don't fully understand why you would want to do this (delay) but would setting the Auto EQ for Absorb voltage and to start every 2 or 3 days do what you want ?
boB
Hi boB,
For me, the average DOD of the bats on my systems is small. Most days with reasonable sun, the SOC gets down to 95 or 96% (SOC). With a reasonable array, and weather, the bank is in Asorb by 10:30 AM, and in Float by 11:30ish AM. So, on days like today, the average Bulk current might be 18-20 Amps. In the case of dealyed daily recharge, if one delayed charge initiation until solar noon, for example, would expect to be in Float by 3:00 PM or before. This would result in a much higher average battery charge current. There are those who recomment approaching C/10 charge rates (ie 10% of 20 Hr AH capapacity) for optimum battery health. I do not exactly subscribe to this, but would like to approach 4 or 5% of capacity rates during daily recharge. Realize that one could skim all of the available PV power in the morning, and sop at noon etc. But, the Classic does know the time of day.
The above is my reasoning for off gridders.
There are some who say that for good battery health, each charge cycle should be from a point of 90% SOC or lower -- one should use a minimum of 10% of capacity before recharge. This is the reason for my desire for delaying recharge for several days when a system is being lightly used. This might happen when the system powers a weekend cabin etc. These approaches are not foolproof, as the weather can always intervene, causing the recharge to get behind the curve.
Will think abut the Auto EQ approach.
Yes, some of ARE too obsessive on this stuff. But, you folks are obsessive about cramming a huge amount of functionality into your products, like the Classic. Thanks, Vic
Yeah, you're basically talking about "Vacation Mode" which the auto EQ will kind of do for now.
A real VM coming up eventually, BTW. We've talked about this.
Ideally, SOC or SO Discharge would be the way to go, that is, unless you knew that there would
be no sun for a while and then you'd want to get it charged sooner.
boB
i'm not following the reasoning behind this either for if it goes to absorb early it's either because you didn't drain off that much of the battery capacity or you have excess in pv or both. if the batteries are getting their full charge then that's a good thing no matter if it was at a lower charge % or not. in fact it is known that a slow charge is a better charge, but few in solar can get it just right because of solar's limited time frame for production. of course you don't want it too low or it may never charge too.
Quote from: boB on April 16, 2012, 02:56:37 PM
I don't fully understand why you would want to do this (delay) but would setting the Auto EQ for Absorb voltage and to start every 2 or 3 days do what you want ?
boB
boB, not sure if your question is addressed to me or the other poster's but my reason is this...My batteries call for 25 amps or more of charging current per battery for best battery life. With 2 batteries in parallel that's 50 amps and I'm putting out 18-19 amps best case. But normally the batteries are hitting absorb before noon so my charging current peaks out much less than 18 amps unless I am running a load. So I thought by delaying the charging I could start the charge cycle closer to mid day to take advantage of the best sun angle. I admit this is not something most people would want to do but I figured it wouldn't hurt to throw out there either. In reality it may not help the batteries at all to get 18 amps instead of 10 so I'm probably spending too much time thinking about this stuff. I haven't tried EQ'ing yet but I was thinking you just manually turn it on or off. Either way my batteries are agm's so I'm not planning to EQ. I can't exceed 15.0 volts.
Quote from: Wxboy on April 16, 2012, 08:58:24 PM
Quote from: boB on April 16, 2012, 02:56:37 PM
I don't fully understand why you would want to do this (delay) but would setting the Auto EQ for Absorb voltage and to start every 2 or 3 days do what you want ?
boB
boB, not sure if your question is addressed to me or the other poster's but my reason is this...My batteries call for 25 amps or more of charging current per battery for best battery life. With 2 batteries in parallel that's 50 amps and I'm putting out 18-19 amps best case. But normally the batteries are hitting absorb before noon so my charging current peaks out much less than 18 amps unless I am running a load. So I thought by delaying the charging I could start the charge cycle closer to mid day to take advantage of the best sun angle. I admit this is not something most people would want to do but I figured it wouldn't hurt to throw out there either. In reality it may not help the batteries at all to get 18 amps instead of 10 so I'm probably spending too much time thinking about this stuff. I haven't tried EQ'ing yet but I was thinking you just manually turn it on or off. Either way my batteries are agm's so I'm not planning to EQ. I can't exceed 15.0 volts.
It might have been directed at you.
Either way, it should not matter when it gets its bulk charge. And as Niel mentioned, slower can be better.
What matters is that the batteries get their Absorb cycle for as long as they need to. If it takes a few hours in the
morning for the batteries to Bulk charge, then as long as they stay in Absorb for a couple of hours or until
their ending amps set point is satisfied, it should not matter.
If it is just a timed Absorb cycle, as it usually is, if you are away most the time, then the batteries don't need
and probably should not be Absorbed for 2 hours every single day. It uses up water and ~may~ decrease
life unnecessarily. That's what I thought you guys meant. Now I see. It's fine either way though.
What you are talking about doing certainly won't hurt anything... I just don't see that it is necessary.
BUT ! Sometimes I miss something obvious and this could be one of those times !
Thanks,
boB
Well, the neat thing about batteries used in PV systems is that everyone has an opinion, and everyone CAN be correct.
Some of us, myself included, may spend too much time wondering of these things and obsessing over the last detail.
Some batt mfgs DO spec a C/10 Bulk, constant for the total duration of Bulk. This is essentially impossible for any reasonable PV array and battery capacity in off grid. My interpretation is that one should have the capability of charging at C/10, but only do so on occasion -- every month or two. Surrette says that this high rate charge freshens the exposed material of the positive plate, and maintains capacity.
I do like, and use EA for Asorb termination. I like your idea, boB about setting an Auto EQ every few days, but would really like it to be sensitive to the global EA value in the case of the periodic Asorb stage. Timed Asorb does not work well in systems where the DOD varies quite a bit.
And Wxboy, sorry kinna hijacked the thread. I do manually stop charging on some mornings to do just what you suggest -- delay charging to increase the charge current. Vic
Quote from: Vic on April 16, 2012, 10:29:34 PM
Some batt mfgs DO spec a C/10 Bulk, constant for the total duration of Bulk. This is essentially impossible for any reasonable PV array and battery capacity in off grid. My interpretation is that one should have the capability of charging at C/10, but only do so on occasion -- every month or two. Surrette says that this high rate charge freshens the exposed material of the positive plate, and maintains capacity.
I suppose there could be something to that... I wonder what "freshens" really means though ?
Maybe it reduces sulfation like Absorption does ? Is there some more info from Surrette or
anybody else on this ? I'll check my literature too.
If it really is a big deal, then we could take a look at this. I have had similar (related) ideas to this delayed charging, but
it had more to do with different finishing times rather than delaying the charging. But most people do not want to waste a drop
of energy so it would have to be disabled by default.
The harder you charge, the warmer the battery should get and that should also lower the Absorb voltage at least for a while.
If the charge rate is too low for a system, it could be that the user can't get the Absorb cycle to complete often enough and
it kills the batteries early just from frequent undercharging.
Thanks,
boB
boB,
Regarding the freshening that Surrette mentioned in a Bulletin, it was stated that for large battery banks, deep discharges (with attendant hi-rate recharge) drives electrolyte deeper into the active plate material, which helps open fresh reaction sites.
The above was from Surrette Bulletin 614. This bulletin has been edited several times. It was deemed as "contraversial" within Surrette Engineering. I believe that this bulletin is no longer on the Surrette site, altho, for now the later version can be seen here:
http://www.altestore.com/mmsolar/Others/Charging_and_Discharging_BU-RS-614.pdf
Believe that the most contraversial point in the Bul 614 is the recommendation to take the bank to about 20% SOC, quarterly, and charge the snot out of the bank to bring it back to 100%.
There seem to be no absolutes regrding off grid battery system chrging/maintenance. Every mfg has a bit different cut on things, and these cuts can change over time.
Really, the first course of business for battery banks it to fully recharge almost every day. But once this is accomplished, routinely, then the obsessive (me) want to do the most possible to try to get maximum life span from the bank. This brings up the million opinions, and "solutions". It is almost impossible for me to figure out what to believe.
Hope MN will do a stand-alone Batt Monitor with some general purpose control functions, such nitwits like me can play around with some of this stuff.
Thanks again, Vic
if memory serves me i addressed this question for him already somewhere on here or on naws. i believe he has sears agm batteries.
niel, you are the one that prompted me to ask this question in the first place. Since you pointed me to the manufacturers information regarding the batteries I decided to ask about delayed charging options. This is because the manufacturer specifies the batteries should be charged at 40% of the 10 hour capacity rating or higher. You did also say not to worry about charging at that rate but I just figured I would bring up the topic to see if others had kicked around the idea.
And I think the point of the high charging current for the batteries is to help de-sulfate the plates. There was a review on the Sears website where someone was charging these batteries with 2 135watt panels and after 4 months 2 of the batteries were not performing as well as when they were new and he suspected sulfating. So this is really what prompted my thought process on all of this.
I was fully prepared to have everyone tell me I was out to lunch with my idea so no big deal.
This is all good stuff and information, WXboy...
It might be interesting to hear from other companies about this idea though.
It is my experience that just Absorbing properly or Equalizing often enough
would help to prevent sulphation but there can still be good information
coming in even after 100 years of charging lead acid batteries.
We're open minded here.
Thanks !
boB