Midnite Classic goes to Float before Battery SG is 100%

Anawa · January 2018

I'm looking for some help with the issue described in the title: Midnite Classic goes to Float well before Battery SG is 100%. Hopefully, some of you knowledgeable Midnite Classic jockeys will lend me a hand.

I've just completed an off-grid install: 9.54 kW PV array, 48 volt, Outback Radian 8048 inverter, 3-Midnite Classics 250's, Mate3 com, 1,100 ah forklift battery bank, and Kohler 8.5 generator. The system has been in service since October (2017) and until mid-December, we had to charge the bank via the generator because of delays associated with erecting the stand-alone PV rack. I'll share the story about the rack erection delay in a subsequent post so that other folks will not make the same mistake. Back to the most pressing problem.

At considerable cost for propane and power inefficiency, we pretty well maintained the battery SG charge above 90%+. I pay no attention to the battery gauge on the Mate3 and rely totally on the SG for SOC accuracy. I measure SG with a HydroVolt device. Many days while on generator, the SG reached 1.285. I only use the Mate3 SOC value to start the generator at low-SOC after I've synchronized the values by SG and the Mate3. Sometimes the percentages between the measurements drift 15-20% apart so constant SG measurement is done. Incidentally, we've equalized a couple of times as the SG varied between cells. There were a couple of times the SOC (by SG) did drop to about 50%. I think we caught it within a few hours, hopefully no significant damage was done.

After the PV was brought on-line and I understood the basics of programming the Classics, everything seemed to be okay. Early during the maximum charging window, we were getting as much as 100 amps+ at 53-55 volts. I didn't think that was too bad for a dead-winter PV production. But, as anticipated, the current dropped significantly as the voltage increased to the absorb setting. It seems to me to be a rather steep decline when the Classic was going into the absorb stage. I've been tweeting the settings frequently and, due to the cold and maybe other issues, I've bumped-up the absorb volt incrementally to now 60v.

Other Classic settings are: End Amps = 8, Absorb Time = 5 hrs, Float Voltage = 59. All these settings were done incrementally with the high float voltage being a means to raise the SG.

These are the first Classics I've used. All of the above is info to consider in helping me through this issue. I'm not sure of the questions I should be asking, but it seems that something, either in the settings or the Classic equipment, is indicating the batteries are fully charged (long before they actually are) and the controller kicks into the float stage.

Thoughts and guidance appreciated.

Thanks
Paul

westbranch · January 2018

Paul, did you use the MNGP or the Local App to enter your data? I have to assume you saved every entry if you used the L.App...?? That may be it or you did not fill in some of the battery data fully/ properly...
hth

Anawa · January 2018

W/B, I used the MNGP. I'm not familiar with Local App.

westbranch · January 2018

It is much easier and faster for checking and changing any parameter. need a laptop and be connected to your router (Wifi)

Vic · January 2018

Hi Anawa,

Would expect that you would need a Absorb voltate (Vabs) of 60, or so volts, under normal conditions, and even higher is you are not able to fully-charge the battery, several times per week.

It is OK to discharge a Forklift battery below 50% SOC, but it would need a full charge soon after that discharge.

So, assume that the Classics are in Follow-Me, and that the Master Classic has a Battery Temperature Sensor on it.

Check in the in the Charge > Limits menu that there are appropriate settings for Min and Max voltages for your flooded battery.

If your battery is not getting fully-charged by actual SG measurements, then the Vabs needs to be raised, or the Absorb time increased. Normally for off-grid systems, raising Vabs is the best thing to do in Winter, as the solar days are usually short ...

FWIW, Vic

mike95490 · January 2018

The Classic has all parameters adjustable via the Local App. (it runs via Adobe AIR) You can Save all the settings via LA, and re-upload them too.

If your batteries are not reaching 95% by the end of absorb, raise the Bulk & Absorb voltages slightly ( try 2 tenths at a time) till you have enough voltage to complete Absorb. Float is for Grid powered chargers, to gently finish off the charge without bubbling the electrolyte, but float should take 5+ hours to complete - not possible off grid.

Off Grid, you balance either on the razor edge of excess charge (+plate corrosion) or under charge (sulfation) Without hours of Float,

Raj174 · January 2018

Hi Pual,
Hopefully you have the wizbang jr installed to make the end amps setting more accurate, also the battery efficiency setting could be an issue if not correct.

This is a link to Midnite's video library. They cover the installation and use of the local app, the follow me setup and more.

http://www.midnitesolar.com/videoDisplay.php

It may no be related, but what is the array VMP at each controller? I ask because if you are using 72 cell panels, 2 in series, then changing default MPPT mode setting from "Solar" to "Legacy P & O" could result in a 10 to 15 percent increase in PV production. At least it did for me.

Rick

Anawa · January 2018

Thanks guys! As usual, you all have been helpful.

Rick, thanks for the video link, it makes things easier for me. The array is made-up of 36 Kyocera KD265's in 3-strings of 12, with 6 paralleled for combined Vmp of 186 per controller. The panels are 60 cell. I'm not sure I can install a whiz bang Jr as I'm integrating these controllers with the Outback equipment, But, would like to explore the possibility if I can get more accurate battery data. With the Outback Mate3, about the only accurate measurement I feel comfortable with is the battery in/out current reading on the FNDC. Also, is the WBjr internet capable?

Mike, thanks for the overview. I kinda figured-out by experience what you mean by being on the razors edge with off-grid battery maintenance. I'm glad I invested in the "less expensive" forklift battery for my first bank. I hope I'll make it for 3 more years before I have to replace. I'll continue to bump-up the Vabs incrementally. Does adjusting the Charge > Limits min/max values raise the Bulk voltage with the Classic's? Is there a Bulk charge setting I'm missing?

Vic, the controllers are in Follow-Me sync and the master has the BTS. I'm apparently sensitive to the "off-grid razors edge" as I find it difficult to increase the Vabs above 2.5 per cell. Although I've read on this forum about going higher to 2.55 or so, it's something I like to contemplate before just doing it. I'll just start with the .2 increments and see what happens. You boys stand-by.

W/B, thanks for the heads-up on the local app. Programming with the MNGP is brutal! I would just as soon be taken behind the barn and whipped real good than have to re-program all of them again with the MNGP!

I've also learned that off-grid batteries don't like the cold. We've had very mild winters here in Georgia for the last few years and never experienced how contrary the batteries can get when they are really chilled. But, as most of y'all probably know, right now things are bit brisk here in the sunny south, as well most every where in the USA and Canada. I suppose that accounts for some of need to increase the Vabs. You reckon?

Thanks
Paul

Anawa · January 2018

Another bit of info for y'all to contemplate.

I've noticed that in the latter stages of Float, the battery current stays fairly steady at 5 +/- amps. Is there any correlation in this and the Absorb End Amps value?

Also, if the increases in Vabs do not fully charge the battery before the Float stage kicks in, is there any wisdom in increasing the Float value to the Vabs value?

Just Asking
Paul

Wbuffetjr1 · January 2018

Paul

I'm in NW GA.
Where are you at in GA?

Anawa · January 2018

West and bit south of Atlanta about 30+ miles, as the crow flies.

mike95490 · January 2018

In the Classic, the Bulk setting is the same variable as the ABSORB. the controller outputs as much as possible while in Bulk, while the battery voltage rises. Once the voltage reaches the Absorb setting, that starts the Abs timer. When the timer runs out, that terminates absorb (where the batteries are bubbling pretty good) and the voltage shifts to the Float voltage setting.
If the batteries are not completing charge, kick up the Abs voltage, that causes more amps to go into the battery for longer times.

Lead-Acid batteries have a quiescent charge amps, where the voltage does not rise further, but the amps going in, continue the charge process. With lead acid, fresh new batteries have low float amps. As they age and wear, the float amps increases

> Charge > Limits min/max values
I've never adjusted this, you might look at the midnight forum http://midniteftp.com/forum/index.php
for more answers

Vic · January 2018

Hi Paul,

Had mentioned the following, previously, ..."Check in the in the Charge > Limits menu that there are appropriate settings for Min and Max voltages for your flooded battery"...

These Charge voltage Limits have probably been added to the Classic Firmware primarily for AGM batteries (perhaps others, too). These Default to relatively low ranges for Flooded batteries.

There is no real guidance on the manual, BUT for your Flooded batteries you will want the High Limit set, such that you can reach the target Vabs and EQ voltages when the battery is cool/cold (particularly if you set the EQ voltage to be temperature Compensated.

Similarly, you should set the Low Limit, low enough that a warm/hot battery can reach its required compensated voltage when the battery is warm/hot. Of course, one should keep one's batteries from getting hot, and this Low Limit could help reduce the (rare) situation of Thermal Runaway ...

Just my opinions, Vic

Raj174 · January 2018

Paul,
I have a Outback Radian GS4048A and a mate3 with a Classic 150, but did not go with the FNDC because I wanted to use the whizbang jr. battery monitor. I have used both, but I think the WB jr. works better with the Classic controller. The WB jr is about 50 dollars, and I believe you could use both monitors in your system if you can mount it on the shunt. Not sure how the shunt is set up in the GSLC. I assume that is what you have. I used a Midnite epanel in my system.

Here is a good review of the Classic by one of the forum members, Zoneblue. It's a good read, and informative.

http://www.zoneblue.nz/cms/page.php?view=midnite-classic-review

Rick

Anawa · January 2018

Rick, I read through ZB's Classic review, a good read indeed. Looks like I'll be tinkering around with the Classics some more.

Thanks all Y'all
Paul

Vic · January 2018

Hi Paul,

Just in an effort to try to be clear, you had mentioned that your weather was on the cool/cold side. And, you made no specific comment regarding you had checked/changed the Classic's Temperature Compensation Voltage Limits;

SO, please, please DO check where these Limits are set (probably at the Defaults), and make certain that these Limits are NOT set SO low, that cool/cold Flooded batteries (like yours) are not reaching sufficiently high Vabs, or, if EQ IS temp compensated, your Veq is not reaching a high enough voltage to Absorb, or EQ your battery.

Would you please acknowledge that you have received and understand this transmission ??
FWIW, Thanks, Vic

Anawa · January 2018

Vic, I really appreciate you following-up on my situation. Dedication by folks like you, and the many other active members, make this forum a place to gain PV knowledge and learn some really meaningful stuff.

I made several adjustments to the Classic's and I think I bumped the max limit up to 63-64. But, I will verify tomorrow and keep you posted.

Thanks Again,
Paul in Georgia

mcgivor · January 2018

Have read the entire thread, but so far nothing has been mentioned about stratification, forklift batteries are extremely tall, despite not being a particular concern in mobile applications due to constant movement, it is believed that this can be an issue in stationery applications. Typically in traction use the battery receives an extended charge, overnight for example, in off grid applications only a small window of opportunity is available, therefore they would need to be hit with a high rate of charge to achieve this goal, allowing gassing to stir the electrolyte in the absence of movement. As @mike95490 mentioned it's a razors edge, upping the bulk/absorption voltage in small incrimants until gassing occurs would be benificial. Schneider controllers have a feature which allows the first hour of absorption to be programmed at a higher value before dropping to a normal setpoint, this allows for a mini EQ of sorts, not actual EQ voltage but a value somewhere between the two, which allows gassing to prevent stratification, at the expense of water loss. In leu of this feature, finding a setpoint to provide a similar effect may be what is required, the value of which is largely dependant on the specific system and how it is used.

Photowhit · January 2018

Well, several concerns, first you say;

Anawa said:

I'm glad I invested in the "less expensive" forklift battery for my first bank. I hope I'll make it for 3 more years before I have to replace.

I am going to make a guess you purchased a GB battery? Are you using their 20 hour rating? GB over estimates their batteries capacity in the 20 hour rate by a large amount. I have one, What they call a 804 amphour battery is realistically about a 650 amp hour battery. We have a thread about this somewhere.

Anawa said:

After the PV was brought on-line and I understood the basics of programming the Classics, everything seemed to be okay. Early during the maximum charging window, we were getting as much as 100 amps+ at 53-55 volts. I didn't think that was too bad for a dead-winter PV production. But, as anticipated, the current dropped significantly as the voltage increased to the absorb setting. It seems to me to be a rather steep decline when the Classic was going into the absorb stage. I've been tweeting the settings frequently and, due to the cold and maybe other issues, I've bumped-up the absorb volt incrementally to now 60v.

Other Classic settings are: End Amps = 8, Absorb Time = 5 hrs, Float Voltage = 59. All these settings were done incrementally with the high float voltage being a means to raise the SG.

Several things sound like you might misunderstand a few things. The dead of winter will be your highest production at any 1 time. Panels produce more energy when they are cold. In the heat they will produce less energy. I would hope on cold days you could produce near 70-80 % of your panel rating or more instead of 100x55=5500 - 5500/9700=57%.

The rather steep decline as approaching the absorb setting... is the power/wattage the same? amps x volts=watts If not the battery may already be reducing the amount of energy it's absorbing. I think end amps is generally set at 1-2% of the battery capacity. 8 amps seems pretty low...

If the battery is a 1100 ah GB such as 12-85-17 which GB rates as a 1072 amp hour 20hr rate but a 680 at a 6hr rate and apply crown's more appropriate conversion of about 1.25x the 6 hr rate we come up with a 850 amphour battery. At this point a 10% rate of 85 amps and a 13% rate of 110 amps.

Do you have a temperature sensor hooked up? Why do you have the float voltage so high? Is this to get additional charging? just take end amps off. What type of adjusted voltages are you running? Where do you have your temp sensor hooked up?

Takes some time for a battery to break in and reach full capacity. Generally you should do a commissioning charge and then a equalizing and take SG readings to use on down the road. What were your SG's when you started?

Vic · January 2018

Paul, Thanks for the info. Forget what Inverter/Charger that you are using. With a high quality inverter 63 - 64 V maximum should not be an issue. Believe that the High Limit setting is about 65.5 V on the systems here (13 year old FLAs with 1.265 Target SG).

In general Forklift batteries need fairly high Vabs and Veq -- 1.285-ish SG electrolyte.

On 48 V FLA batteries, about 56.5, or so volts is usually considered the Gassing voltage. IMO, higher SG electrolyte would bump this value up a bit. The higher the Vabs/Veq the more vigorous the Gassing, of course.

In the Winter, 48 V off grid systems often need Vabs of around 60 V. These systems with 1.277 - 1.290 SG electrolyte often need higher-yet charge/EQ voltages.

FWIW, Vic

Anawa · January 2018

Mac, I observe a fair amount of gassing, perhaps because the Vabs is set pretty high. I do find that the water level needs monitoring and I add water quite often.

P/W, yep, GB Industrials. I know you probably do not remember the thread, but it was your recommendation that I consider them for my system. That was in late 2014. Not mentioning this to accuse, only to say thanks for the advice. I think in the long run, forklift batteries for the 1st battery bank makes sense.

Like I said, if I make it 3 more years on this set (6 years total) I will be satisfied. There is no question that for the first few months, I undercharged them. I relied on the accuracy of Mate2 battery gauge in the beginning. I read all the info on the Outback FN-DC on this and other forums trying to make sense out of something that was wrought with error. When I finally wised-up and started using the HydroVolt exclusively to measure the SG, the adjustments I was doing with the charging parameters was actually doing something worthwhile.

Regarding the GB 20hr rating, yep, I read that thread also. The tread pretty well confirmed what I was experiencing, the SOC measured by SG was in no way close to the gauge.

I'll get back to this post directly, gotta do something for my wife.

Paul

Midnite Classic goes to Float before Battery SG is 100%

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