Temp compensation charging values

dapago · November 2016

hello

Trojan data sheet recommends a charging temp compensation by subtracting or adding 0.005V per cel above 25C ambient temp. Does that apply in all charging modes (bulk, absorb, float, eq)?

best.

softdown · November 2016

Constantly changing your charge controller is an exercise that few would want to partake in. If battery temps vary by more than ~20 degrees, a battery temp sensor is in order. That is all that the better charge controllers need to automatically adjust charging voltages.

I have a strong suspicion that many pre-mature battery failures are caused by exposing them to temps exceeding ~95F. I'm actually quite sure of that.

I tried to look up data for charging parameters vs. ambient battery temperatures. Was not able to find a chart though battery temp information is presented: http://www.xantrex.com/documents/Discontinued-Products/XBM-975-0111-01-01_Rev-C(Artwork).pdf

My C-35 charge controllers users book has a nice chart regarding battery temp vs charging voltage. Makes one wonder how automotive batteries survive considering the temps they are exposed to.

BB. · November 2016

EQ is a different animal... You are trying to over charge the battery bank so that any "low cell" will get current through it while the other cells in series simply gas.

I believe some charge controllers do not use temperature corrected voltage for EQ voltage. In any case, your EQ voltage should be high enough to get around 2.5% to 5% rate of charge--You do not want >5% rate of charge if you can avoid it... It will cause the battery to heat up (and over heat) pretty quickly. Even a 2.5%-5% rate of charge can overheat the battery bank if done for many hours (some "corrective EQs" can take many hours or even need to be done over several days.

-Bill

Vic · November 2016

dapago said:

hello

Trojan data sheet recommends a charging temp compensation by subtracting or adding 0.005V per cel above 25C ambient temp. Does that apply in all charging modes (bulk, absorb, float, eq)?

best.

Hi dapago,

In addition to what BB Bill mentioned, YES, only voltage-regulated charge stages will be, or need to be compensated for measured battery temperature. This would be Absorb, Float, and EQ.

Your Classic will compensate these voltages, when you set the Compensation value to --5 mV, and EQ Temp Compensation to YES.

Be certain to set fairly wide Voltage Limits for the compensation range. This means, to choose the low voltage compensation Limit lower than you ever expect the battery compensation to be, and similarly, the high compensated voltage higher than you would ever expect the battery to experience. Since this compensation value is a negative number, the highest compensated voltage will be for a cool/cold battery, and the converse for the low compensation Limit.

For the Classic, the Limits of Temperature Compensation apply, mostly, to Sealed LA batteries. IMO, Flooded batteries would not normally need Limits on compensation for any reasonable battery temperature.

Set the Reference temperature to 25 C (believe that this is the Default in the later Classic FW versions)

Also, IMO, essentially ANY LA battery should use a Battery Temperature Sensor (BTS/RTS). They are inexpensive (included with the Classic CC), and batteries tend to be not so inexpensive.

Vic

dapago · November 2016

i have a temp sensor connected to the batts.
Vic. Sorry I am a bit lost. You are saying that the classic will automatically compensate charging values according to Compensation value if set to -5mV when batt temp at 25C? So you just enter that figure in Compensation value and the classic will do the work according to the type of batts installed?
in my location temp never goes under 25C.

dapago · November 2016

I have the charge volts set as Trojan recommends. So just going to T-Comp menu, enter -5mV and Eq Comp to YES and it will do the trick?
I have the Min T-Comp at 52.1V and the Max at 64.8V (EQ voltaje needed for the batt). Then on the same menu I have Output set at 88Amps and Input at 99 Amps and Hi Batt at 170 Celsius. Is everything correct here?

Vic · November 2016

dapago said:

i have a temp sensor connected to the batts.
Vic. Sorry I am a bit lost. You are saying that the classic will automatically compensate charging values according to Compensation value if set to -5mV when batt temp at 25C? So you just enter that figure in Compensation value and the classic will do the work according to the type of batts installed?
in my location temp never goes under 25C.

Hello dapago,

When a Temperature Compensation value is set (the --5 mV/C that you are using), and Compensate EQ = YES, the Classic will compensate all of the regulated voltages. It will apply these compensations, based upon the Reference Temperature that is set. In the case of most Flooded batteries, this Reference temperature will be 25, or 27 C. You are using 25 C which is correct for your Trojan Flooded batteries.

Regarding the Limits settings, the high Limit is probably OK, although, I would set this a bit higher. Do not know the maximum battery voltage that the Magnum will accommodate, however. Forget the recommended Trojan setpoints, was the suggested EQ voltage 64.4? For now, 64.8 is probably fine ... just might be one cold (for your location) when the EQ voltage might want to be a bit higher ... for now your setting is fine, IMO.

The low voltage Limit would really only apply during Float. IIRC, your Float voltage is around 54.XX volts. The total compensation for your 48 V battery is --0.120 volts per degree C change, from 25 C. So, depending on just how hot your batteries become, would dictate just how low this Limit should be. If the batteries reach 40 C during Float, the total compensation would be --1.8 volts. Your low voltage Limit is close to the correct value. The batteries might be hot after a long Absorb, or an EQ on a hot day.

Will look at your Float voltage setting. But you are in the correct ball park, IMO.

The input current limit is almost never changed from the 99 A. The output current limit might need to be set for your 225 Ah batteries. Depending on temperatures, etc, you might have a maximum charge rate of about 15% of the battery Capacity. This may be fine, as there will probably be other loads on the system during the time that this maximum current would be present.

More later, Vic

dapago · November 2016

Vic, Bill
At 25c, trojan suggest eq voltaje @ 64.8V so I thought setting the max limit voltaje at this value was correct but maybe not as you suggest to rise it a bit. Maybe 65V or 65.5V?
By the way, I did not find the menu where to set the reference temp (25C).
Where can you see the batt temp reached during float?

The Magnum Input Battery Voltaje range from 36VDC to 64VDC and the Absolute Max DC Input is 68VDC.

I did not understand the maths about the Max charge rate and the Output current limit. How do you get 15% from the 88 amps value? Could you explain please? The only frequent load during day time are 1 fridge, 1 freezer and a stereo (2x40w). The rest of the load is not continuous.

Thanks for for your patience.

Vic · November 2016

dapago said:

Vic, Bill
At 25c, trojan suggest eq voltaje @ 64.8V so I thought setting the max limit voltaje at this value was correct but maybe not as you suggest to rise it a bit. Maybe 65V or 65.5V?
By the way, I did not find the menu where to set the reference temp (25C).
Where can you see the batt temp reached during float?

The Magnum Input Battery Voltaje range from 36VDC to 64VDC and the Absolute Max DC Input is 68VDC.

I did not understand the maths about the Max charge rate and the Output current limit. How do you get 15% from the 88 amps value? Could you explain please? The only frequent load during day time are 1 fridge, 1 freezer and a stereo (2x40w). The rest of the load is not continuous.

Thanks for for your patience.

dapago,

Believe that the Classic uses 25 C as its internal Reference Temperature for compensating voltages that are compensated.

The SETTING for a Temperature Reference is in the Setup Menu for the WhizBang Jr (the battery current monitoring accessory) ONLY -- my error. Have only been using systems with this inexpensive accessory since 2013, and forgot ... sorry.

For the upper voltage Limit, probably 65 V is fine. You might try asking Magnum about this Maximum CC output voltage in EQ, and what effect this might have on the inverter performance, and weather certain parameters would still meet specifications at 64.8 or 65 V (like AC output voltage specs).

Also, you may want to check the High (battery) Voltage Disconnect, or similar menu setting in the Magnum inverter, as this may well be set to a lower default ... would guess that this is probably an available setting with the Magnum remote panel gizmo.

The Battery temperature, measured by the BTS, and several Classic internal temperatures can be seen the 'Temps' menu.

You probably do not need to set the Classic output current Limit, really.
Just used 0.75 X 2480 W of the PVs to estimate the approximate PV power in full sun. Then divided this by a battery voltage that is a bit below Absorb -- 57 V, IIRC. This gives an approximate charge current that might be delivered to the battery (with NO load on the inverter). This was about 32.5 Amps. 13% of your battery 20-hour Capacity (225 Ah) is 0.13 X 225. This yields about 29-ish Amps. With fairly warm PVs and a bit of a load on the inverter, etc. you are probably fine.

But, you could set the Classic Output current Limit to about 35 A or so, if you want. In your generally warm/hot climate you might find that in midday sun, on a typical day, you may not see 75% of rated (STC) PV power when in Bulk.

FWIW, Vic

Vic · November 2016

dapago,

Do not recall, if it has been suggested that you should be using a good quality Hydrometer to measure, and record in your battery Logbook the SGs of each cell in each battery.

If you have not done so, yet, it is a very good idea to number each battery (like 1 - 8), and each cell of each battery (as in A - B - C), using a felt-tipped pen. This logging of measured data will help you follow trends SGs, verses your entries regarding Absorb voltage, time, EQ date, time and voltage, water consumption and addition and quantity of Distilled Water, etc.

A Hydrometer with a glass outer tube, and glass float should serve you well.

Here is an Article on measuring SGs from Surrette battery. The only real difference between Surrete Solar batteries and Trojan, is that the target SG for your Trojans, is 1.277 (Surrette uses 1.265 SG):

http://support.rollsbattery.com/support/solutions/articles/4347-measuring-specific-gravity

Vic

dapago · November 2016

Vic
Lot clearer now!! Many Thanks.
So if I well understand, 13% charge current capacity is the best setting for charging my 225Ah batts or 29.25 Amps with no,load on the inverter.

You suggest not to set the output current limit and leave it at 88 Amps. At midday full sun the charge current capacity would then be over the 13% charge rate recommended (at 20 hours capacity rating no load or just a few amps used by the inverter). Would that be ok?

On the other side if I set the output current limit at let's say 35 Amps as suggested, at midday full sun nearly every day I wouldn't get the full array capacity when in bulk.

I suppose then it is a decision I have to make according to how fast I need my batts to be charged and that depends on my daily loads and needs.
Now if I want to preserve my batts keeping within the recommended 13% charge rate and I have enough daily sun, it would be better to limit the output current at 35 Amps. Am I correct here?

attached magnum defaults values and spec.

dapago · November 2016

Vic. Yes you suggested that in an earlier post. I have bought one and couldn't get it work properly until I realized the hydrometer inside the glass tube was mounted up side down.
I ordered as well a batt monitor. Isn't a batt monitor more practical if the objective is to know your SOC than having to tediously measure the SG of 24 cels?

will check your link. Thanks for sharing

Vic · November 2016

dapago,

Thanks for the Default values. Looks like your inverter does not have a High Battery Disconnect (or cutout) value. So, no need to worry about that.

For now, why not just leave the Classic output current Limit at 88 A. The odds of your PVs delivering much more than 29 Amps is small, due to probable high ambient temperatures.

One main consideration for Battery Monitors, is they, at least, need to be Calibrated using measured SGs. And, then, calibration drifts, due to a number of variables that the system manager is probably not even aware of. One large factor in determining the actual SOC, depends upon the Rate at which the energy was removed from the battery (discharge current). Most battery monitors ignore this value. And there are a number of other factors that are not accounted for. Furthermore, each battery design behaves a bit differently, and these variables are generally unknowable to the system manager.

Battery monitors can be useful in giving people a rough idea of the approximate SOC of the battery. But they (IMO) should not be considered an absolute read on the SOC of a battery.

You ARE lucky, bechaus you have chosen Flooded batteries, which allow the actual SOC to be measured, with a Hydrometer. This is much better than needing to try to guess SOC. Sealed batteries are not this friendly, IMO.

Just my opinions, Vic

dapago · November 2016

Thanks Vic.
coming back to EQ mode. So now I have set EQ T-Comp to yes what about the Amps during EQ?
Bill said that that during EQ charge rate should be <5% charge rate but at midday in full sun with no load it can reach 30ish Amps. Does the classic has a function to reduce Amps during EQ to meet the <5% charge rate or does it raises the voltaje and reduce the Amps to meet requirement?
Does the MidNite batt monitor that I just ordered takes the Discharge Current Rate into consideration or should I order a different one? The main idea to have a batt monitor is to get an accurate reading I would think. The reason I bought the MidNite MNBCM is that on its brochure, it advertises No Calibration needed and an accuracy of +/-1%.

softdown · November 2016

Not a geek but have this to generally say about battery voltage vs specific gravity. Battery voltage will broadly tell you if a battery is *probably* good or bad. Specific gravity will tell you exactly tell you what the battery health is *and* exactly what the health of each cell is. I might estimate the correlation between specific gravity and voltage to be ~90% or so.

One may think that a 2 volt cell showing 2 volts is OK. This is not true. The difference between a 2.2-2.4 volt cell and a 2 volt cell is very dramatic. Specific gravity readings will highlight the dramatic difference in cell health. A cell may show 2 volts while specific gravity readings are closer to "water". Most SG meters do not read below 1.1100. Anything below 1.1200 is critically low. Anything below 1.1250 is not good. A good reading is ~1.127....though some batteries are designed to have a high SG reading. A few are designed to have a lower SG reading. It seems that solar batteries are designed to have a reading between 1.265 and 1.275.

A good SG meter is a must have for lead acid users. Battery voltage will tell you if there is a problem. SG will tell you where the problem is and how big the problem is.

Most of our active posters here are solar pros. Pros and cons to that. Their level of geek detail may intimidate all but highly experienced solar enthusiasts and some geeks. I feel like some may invite their customers to follow them here and are consequently constantly pushing their product line and line of reasoning. Just a part time theory by the way. Well...different things can work. This is no "one best way" that applies to everybody.

BB. · November 2016

Equalization is controlled over charging of the battery bank... I have not read the details of the Wizbang Jr--But the nominal way of limiting EQ current would be to drop the voltage set point until is a more reasonable 5% or a bit less. To much current will create a lot of gas and heat--And will damage the plates if done "too much/too long".

You want the cells "fizzing" rather than a rolling boil during charging/EQ.

For any "shunt based" battery monitor--They can "drift" in their State of Charge readings (sort of like using the gasoline pump numbers to fill your tank based on your average fuel economy... Drive 100 miles at 20 MPG average = 5 gallons of estimated fuel usage--At the pump, you put in 5 gallons of gas). The only time you know the tank is full at the pump is when gas starts coming back out the fill tube (or trips the auto shutoff of the pump nozzle).

That will work for awhile, but eventually you will either over fill the tank or the tank will run dry (your estimated MPG factors for city/highway/idling/etc. is not 100% accurate).

For battery monitors, the generally reset to 100% after the battery has been held at 14.7 volts (for 12 volt battery) for 2+ hours (or whatever is use for a specific monitor). Then the battery monitor assumes the battery is now 100% full.

-Bill

dapago · November 2016

Thanks. If i well understand, a batt monitor is a day to day device to Check your "relative SOC". SG testing when your batt monitor shows a reading not conform with onsite reality. I have 24 cels and they recommend to check every cel twice during a testing and keep a log of it. That is a lot specially when the protocol is not simple to say the least.

Vic · November 2016

dapago said:

Thanks. If i well understand, a batt monitor is a day to day device to Check your "relative SOC". SG testing when your batt monitor shows a reading not conform with onsite reality. I have 24 cels and they recommend to check every cel twice during a testing and keep a log of it. That is a lot specially when the protocol is not simple to say the least.

Just a quick couple of thoughtsl

There is no specific limit of EQ current into the battery, yet ... have suggested this to MidNite Engineering.

As BB Bill noted, one can (and I often DO) step up the EQ voltage in several steps, to limit the battery current.

Regarding the MN Battery charge state LED meter, this is an OK device ... it just looks at battery voltage in previous time intervals to judge how well charged is the battery, just a quick approximate read. Shunt based meters will be more accurate.

The MN WbJr plus a Shunt would be a good addition to dapago's system, both are on this page:
https://www.solar-electric.com/midnite-solar-whiz-bang-jr-current-sense-module.html

As an aside, battery voltage is not a particularly good indication of SOC of a battery bank, especially that is being charged/discharged 24/7. One needs to know the battery temperature, and approximate charge and discharge that has occurred in the previous six, or so hours. We CAN learn to correlate battery voltage, say, early in the AM to approximately what this may mean for SOC, especially if the system has relatively consistent discharge at night, from one night to the next.

FWIW, Vic

dapago · November 2016

Vic. I am sure the WBJR is a better call but the price the dealer is offering for that is too high. In the US you can get the 2 devices for a fair <$100. Here it goes >$250. I will have to buy one eventually but maybe can wait until someone bring one with him if visiting Nicaragua. Maybe one night stay offer on an island can incentive somebody

About limiting current for EQ that would be a nice feature and I am surprised it is not already implemented into the classic software. How do you step the EQ and limit the battery current?

BB. · November 2016

Just adjust the EQ set point/charging voltage... Start on the low side (say 60 volts), and see how much current is going into the battery bank during EQ--Adjust set point up/down (by a few a ~0.5 volts or so for a 48 volt bank system)... You should quickly see what voltage gets you to ~2.5-5% of rate of charge (as battery cells equalize/temperatures change/etc., you may adjust during the EQ process.

-Bill

Vic · November 2016

On the Classic, if one changes the EQ voltage, it takes effect immediately. So, one would do a full charge through Absorb, start EQ with the EQ voltage somewhat above the Absorb voltage. After a 20-30 minutes would step it up 1.5 - 2 V on a 48 V system, and so on.

One advantage of the WbJr, is that is allows one to monitor the charge current going into the battery. With light loads on the inverter, the Classic's output current is also a good indication of about what is this battery current. The Classic has an accurate output current indication.

Vic

dapago · November 2016

ok. Right now IN =102.5V y 1150 watts. So that gives me 11 Amps charge current. 225x0.05=11amps so that should be ok. Hope I have the maths right here. BATT says 63.5V, not reaching the 64.8V recommended by Trojan so.

BB. · November 2016

Just give it time... Check your cells, and find out which one(s) are low SG. Watch them--When they stop rising every 30 minutes or so, (all cells stop rising), then the battery is EQ'ed... And the new readings for each (log them) are now 100% full.

-Bill

dapago · November 2016

I have to check every cels for SG during the EQ process? That is 24 cels and it takes me a long time to do
that. Wouldn't it be better give a specific EQ time?

BB. · November 2016

You are trying to bring up under charged cells.

The fully charged cells are not going to rise. The (hopefully few) low sg cells will rise. So, two or three cells to check. When they stop rising, corrective eq is done (need to make sure no bubbles on float, log temperature corrected sg (as temp rises, sg drops).

There is monthly eq to mix electrolyte (tall case batteries especially) that is a timed eq (I don't remember, 1 hour?) to mix the electrolyte.

-Bill

dapago · November 2016

Why there is not a system with multi mini SG tester you plug on each cell and keep them connected that can gives you a SG reading at all time without having to uncap each cell, takes the liquid out, put it back in and cap it again? or maybe it exists and if so I WANT ONE

BB. · November 2016

Not cheap, each sensor needs calibration, fragile.

http://www.eepowersolutions.com/categories/digital-hydrometers-density-meters-sg-series/

-Bill

dapago · November 2016

Nice feature. I was thinking of something lot more simple

Vic · November 2016

Hi dapago,

Initially, you could have measured the terminal voltage of each battery, measured the SG of each cell, and recorded this data in your Battery Logbook. This survey would have allowed you to note the lowest SG cells, and then you would have been able to monitor those lagging cells. during the first EQ.

Then you could have fully charged the battery, and then done a Commissioning EQ, to commission the battery bank.

Most of us do not do the above on our first new battery bank, as we did not know to do so. Some manufacturers recommend the this procedure on a new battery bank in their Flooded Battery Manual, many do not.

After a Commissioning EQ, as BB Bill noted, check the SGs of the entire bank, noting the cells on which the SG simply would rise no more. This/these cells will become your Pilot Cells -- cells which can be used as a quick read on the SG of the battery.

SG readings need to be compensated for temperature variations from the Reference temperature of 25 - 27 C (27 C for Trojans IIRC). EQing a battery that really needs an EQ (and therefore requires a long EQ), can cause significant temperature rise, and therefore it can be important to pay attention to what IS the battery temperature, and weather the Hydrometer that is being used does a temperature compensation.

Adding Distilled Water to batteries, and measuring SGs is not that time-consuming -- we get better and better at doing these things. It is important, when designing the layout of a battery-based system, to make battery accessibility a top consideration. The easier on you that these process are, on you, the more likely they will be done well, and in a timely manner ... and so on.

FWIW, Vic

dapago · November 2016

Vic. Sorry for the delayed response to your post.
I suppose with time and experience taking the SG will be much quicker for me.
Sorry but what do you call a Commisioning EQ? I learned about maintenance and rescue EQ but never about commisioning EQ. Or maybe it is an other term for data log each cel. sorry if I make stupid question but I want to be sure of everything. Those batts cost me an eye.

westbranch · November 2016

For an example: see page 6 sec. 2.8 and 3.2.1

http://discover-energy.com/sites/default/files/shared/RE_Installation_Commissioning_Operations.pdf

Temp compensation charging values

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