Is it dangerous or bad to increase the absorption voltage?

Rngr275Rngr275 Solar Expert Posts: 101 ✭✭✭✭
Let me explain in more detail why I am thinking of this and what I am hoping to accomplish.

We just had 2 days of great almost all day sun here. Last night I checked my SG and it was still on the low side (even thought the controller was in float). The SG’s in my pilot cells were 1.25-1.26 vs Trojan’s target of 1.277 +- 0.007 being fully charged. Note: I have been struggling to get and keep the SG up in the 1.27 range.

Here are my controller settings (2-Classic 200’s, “Follow Me” enabled): Absorb Voltage=59.2, Absorb Time= 4hrs, End Amps=7, Float Voltage= 52.8. On day 2 of the sun, the charger went into float after the 4 hours of absorb. On day one there were fewer hours of sun so the charger never made it to float.

What I was thinking (ooh boy here we go) was that; If I knew we were going to be getting some pretty good sun and knowing my SG was a little low, could I bump up the absorption Voltage kind of like a Lite EQ, or lower the End amps or should I increase the absorption time to even more to push up the SG.

It will be sunny today also. If I go home and after another 3-4 hours of absorption @59.2V the SG is still in the 1.25-1.26 range are there variables in the charger that can be changed to raise the SG to “Fully” charged then back down the settings to maintain the SG. Or do I just do an EQ as needed to push the SG up and keep tweaking the charger settings to hold/maintain SG. Or is this the way it is in the winter.

Hope this post wasn’t to convoluted.

Thanx All

Comments

  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Is it dangerous or bad to increase the absorption voltage?
    Rngr275 wrote: »
    Here are my controller settings (2-Classic 200’s, “Follow Me” enabled): Absorb Voltage=59.2, Absorb Time= 4hrs, End Amps=7, Float Voltage= 52.8.
    <snip>
    could I bump up the absorption Voltage kind of like a Lite EQ, or lower the End amps or should I increase the absorption time to even more to push up the SG.

    How did you determine an end amps value of 7? --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Is it dangerous or bad to increase the absorption voltage?

    Looks like the End Amps is set at 2% of the battery bank capacity. If anything this probably too low because it doesn't include a value for load draws.

    Yes, you can increase the Absorb Voltage. How much and what it will gain you is debatable. The higher the Voltage is, the more stress on the batteries (EQ Voltage range; not recommended for more than 1 hour at a time). The first sign of this would be rapid loss of water.
  • Rngr275Rngr275 Solar Expert Posts: 101 ✭✭✭✭
    Re: Is it dangerous or bad to increase the absorption voltage?

    VTmaps...I have looked at the log on the classic a number of times when I had a long absorb time and low EA. It apperas that the amps usually bottom out around 6-8 amps at the end of the absorption. Is the a correct way or do I need to adjust?
    The battery bank is 740AH... wouldn't the 7A EA be more like 1%. Cariboocoot could you explain" If anything this probably too low because it doesn't include a value for load draws"? If I raise the EA to say 10A wouldn't the absorb end earlier than the 7A setting... or am I missing something.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Is it dangerous or bad to increase the absorption voltage?

    Sorry; I misread your battery bank size. 7 Amps on 740 Amp hours is quite low indeed.

    End Amps is typically 2% of battery bank capacity plus an allowance for any current going out of the batteries while charging. Since the EA is measured at the charge controller, it can't know that 1 Amp of the 7 Amps going out is power loads instead of charging batteries. This is why the usual method for setting it is to actually watch the Amps until they stop going down during Absorb. Along about that point the batteries are charged and the current being supplied is running loads and maintaining the Absorb Voltage. That's when you can definitely switch to Float.

    On low daylight days you can Bulk with the generator, set the Absorb time to the max, and see what happens.

    Now for the bleeding obvious questions:

    1). Do you have a remote temperature sensor on the batteries?
    2). Have you ever seen that target 1.277 SG with your hydrometer?
    3). Is Absorb ending due to time limit, End Amps, or just plain running out of sun?

    Probably redundant to reiterate the off-grid bad-weather charging litany of "Bulk with gen, let the panels finish if they can. No sun for three days = run the gen for a full cycle anyway."
  • Rngr275Rngr275 Solar Expert Posts: 101 ✭✭✭✭
    Re: Is it dangerous or bad to increase the absorption voltage?

    CariBoo:
    1. Not that is connected to the Classics. There is one that goes to my Outback Inverter. I do have a stand alone TC that I can use.
    2. No I haven't. Best SG to date has been ~ 1.265-1.275 (adjusted for temp.)
    3. Day one ran out of sun, day2 had 4 hr Abs then went to Float... EA was in the 7-8A range so I think the Charge time dominated EA.

    Haven't had a hard/deep dishcharge of the batteries lowest I have seen/measured has been in the 75% SOC range but typical is in the 85% range.

    Does raising the EA to ~ 14A (2%) and keeping the ABS time the same = less time in absorb?

    I might do an EQ tonight to try and raise the SG to spec. and then monitor the charging.

    Can I start in regular charging mode with the Genny and monitor the amperage to get a good EA and then go to the EQ voltage?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Is it dangerous or bad to increase the absorption voltage?

    End Amps vs. Absorb time limit is a case of "whichever comes first". So if the Amps drop to the set point, Absorb ends even if the clock hasn't run out. If the Amps never drops to the EA then the Absorb time limit will switch to Float when it runs out.

    You really should have temp sensors on the Classics. They are (or should be) your primary charging source. You want them to be as accurate as possible.
    By the same token you should also be able to run a full charge cycle from the generator with the same set points. The goal is to make the two sources interchangeable, but rely on generator power for Bulk when necessary as it gets to be expensive to run it for a few Amps charging during Absorb.
  • VicVic Solar Expert Posts: 2,969 ✭✭✭✭
    Re: Is it dangerous or bad to increase the absorption voltage?

    Rngr..

    You really MUST use the Temp Sensors on each charge source (although, in some configurations, the OB products CAN share a single RTS in some situations), and all of these sensors should be on the same battery near the center of the pack, about half way down the side of the battery. Ideally, the batteries should be in an insulated box that allows the batteries to be at/near the same temps as the rest of the bank. Have been using insulated boxes here, but with the box cover open, to allow heat from the bank to escape the box (yea, this is a bit of an issue with Hydorgen gas control).

    As Marc noted, the output current from the CC toward the batteries includes the inverters and any loads on them. If those loads are fairly constant toward the end of an Absorption stage, all should ve very well in trying to use CC EA as a termninator of Abs. Since you have the FNDC BM, you can see the actual battery charge current. For the banks here that I monitor, the actual battery charge currents for termination of Abs are very close to 1.1% of actual battery bank capacity. Your batteries are somewhat different, and you should be able to find the value that your bank wants, once you can do 100% recharge on a given day.

    Would not hurt to try to run the genset early in the morning, and perhaps the sun will be able to allow a full battery charge.

    YES, raising the EA to a higher value will quite possibly shorten the Abs stage, it depends on weather you can reach that value. For now a bit below 1% of 20 hr capacity might be best until the bank gets fully recharged. Believe that you work on week days, so it may be difficult for you to monitor in real-time the charge progress, but those MN Classics DO have very good logging capability, as you know.

    Regarding EQ, if it is possible, you might want to limit the Inverter's charge current, manually, as the battery approachs the EQ voltage. It is often recommended (although not necessarily by Trojan), that EQ current be limited to 5% of 20 hour Capacity. I forget what the max Charge Current limit is for the OB 3648, but it is probably 60 amps or so, which exceeds 5% by a reasonable amount. And, for doing a solar EQ from PV, you might also want to limit the CC's output current as well on the those sunny cold days. High charge currents in Bulk are often good for a battery (at least some times), so you might want to reset the CC limit at 60.5 or 61 volts (temp comped) manually, and reset to the normal level after EQ.

    Furthermore, IMHO, EQ voltage should be Temperature Compensated. Do not know the environment that your batteries experience, but your location gets COLD, am sure ... believe that you may be one of the wise OG folks with a basement/Root Cellar battery room ... forget. Above are just My Opinions, YMMV. Enough for now, Have fun, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • Rngr275Rngr275 Solar Expert Posts: 101 ✭✭✭✭
    Re: Is it dangerous or bad to increase the absorption voltage?

    I was disappointed that the classics did not have a temp sensor connected to them. I have read that the classic controllers come with the temp sensor. I will check with the installer to see what the deal is and either get them from him or I will order a couple... do I need one on each controller? Did I mention I will order immediately!

    My battery bank is in my cellar in an enclosed and vented box. Not insulated though. Made from 3/4" plywood and lined with a fiberglass sheeting. There is a sensor going from the batteries to the inverter.

    I checked the amp limit from the generator to the batteries in the FX inverter and it was set at 50 amps which is ok most times I guess.

    I did start an EQ and set the current limit to ~30 amps which is less than the 5% of my 740AH battery bank. I noticed that the amperage dropped once the EQ voltage was achieved. Is this normal? I will bump up the current limit once I have finished this EQ.

    I am doing an EQ because the batteries SG was around 1.26 after 3 really good days of charging. Multiple hours of absorb . The last 2 days the chargers went to float at around 1:30-2:00pm. I want to see if I can get the SG up then try to maintain.

    Thanks Guys... you are the best.
  • VicVic Solar Expert Posts: 2,969 ✭✭✭✭
    Re: Is it dangerous or bad to increase the absorption voltage?

    Hi Rngr275,

    Fine on the battery cellar and box, that sounds fine, better than my situations ...

    The EQ seems fine to me. The batteries are probably cool, so, the CC BTS(es) would increase the charge voltage by perhaps one volt or a bit more on your 48 V system, so your 59.2-ish CC V setting is not really that high, and your could increase the CC Absrb V setting to a bit above 60 V without much concern IMHO.

    YES, the Classics should have come with an approx 10-foot bright blue phone style cable with phone type connector. The sensor is a rectangle about 3/4" X 1.5" or so ... you might look around for them, perhaps in the original Classic box. I do not know about Follow Me FW, so it would be safe to use both BTSes. You might ask about this on the MN Forum. Do not recall seeing that mentioned there RE Follow Me.

    And, yes, it is normal that the current drops when the EQ voltage is met, and should continue to diminish as the EQ continues to some point where it may well stabilize, similar to the Absorption stage.

    Your batteries should serve you well, as you are paying attention to them when they are youngsters, and they should grow up well-balanced. Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • PhotowhitPhotowhit Solar Expert Posts: 4,910 ✭✭✭✭
    Re: Is it dangerous or bad to increase the absorption voltage?
    Rngr275 wrote: »
    I was disappointed that the classics did not have a temp sensor connected to them. I have read that the classic controllers come with the temp sensor. ...

    I'm the one who said that in comparison with other CC, Page 11 of the manual says it's so...

    I think they share the temp info, but won't make that claim without more reading.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Is it dangerous or bad to increase the absorption voltage?
    Rngr275 wrote: »
    I was disappointed that the classics did not have a temp sensor connected to them. I have read that the classic controllers come with the temp sensor. I will check with the installer to see what the deal is and either get them from him or I will order a couple... do I need one on each controller? Did I mention I will order immediately!

    For what its worth, the battery sensors of outback and midnite are interchangeable.
    Rngr275 wrote:
    Day one ran out of sun, day2 had 4 hr Abs then went to Float... EA was in the 7-8A range so I think the Charge time dominated EA.
    Are you saying that you did not achieve an end amps of 7?
    7 Amps on 740 Amp hours is quite low indeed.
    End Amps is typically 2% of battery bank capacity plus an allowance for any current going out of the batteries while charging.
    For what its worth, my Interstate batteries have an end amps of 1% of their 20 hr capacity. That is at an absorb voltage of 29.6. If I use the higher absorb voltage (30 volts) that Interstate recommends, the end amps will be a bit higher.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Is it dangerous or bad to increase the absorption voltage?

    Yeah, Interstates are weird aren't they? :p
    That's why I don't have them anymore.
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