Battery Charging with a Trace Inverter - Do I have an issue?

[rv_safetyman]

OK folks.  I have been trying to diagnose a problem that I ***think*** I have.  My battery bank is 8 golf cart batteries (new within the year).  My inverter is a full sine wave Trace model SW2512MC.  I am measuring SOC (state of charge) with a Bogart TriMetric 2020.

My problem is that it seems like it takes a very long time for the battery bank to reach 80-85% SOC and days to reach 100% SOC.

Over the weekend, I worked a vintage sports car race and Pat was in the bus.  She ran the generator for about 6-8 hours each day (very hot outside).  At the end of one day, the SOC was 70% (starting from about 60%).  I finally figured out that I had the input current set to 10 amps (from visiting the relatives).  Today we are back home and in about 6 hours the SOC went from 64 to 70% on 50 amp house service (Trace input set at 45 amps).

It seems to me that part of the issue is the switch from bulk to float.  I have tried setting the bulk to a fairly high time (don't have notes in front of me, but it was well over an hour.

I have done all sorts of testing/setting and nothing seems to jump out at me.

It seems to me like this whole issue started when I replaced the batteries.  I checked the settings on the Trace and TriMetric and I think I have them set for the battery bank I have.

I have tried shutting down the power supply to force the inverter back into bulk charge but the inverter switches to float in a fairly short period of time.

I have done a ton of documentation of playing with the settings, and now I have myself thoroughly confused.

I think I have a problem, but even there I am not sure.

Help

Jim

[luvrbus]

A wiring connection probably Jim check the AC and DC side have you checked for AC reverse polarity that one drove me nuts for 2 days still to this day I do not know how it happen.

There is a good inverter guy in CO/Springs I forgot his name Jim Smith knows it if you need help he is a factory service center and very reasonable on prices if you do need repairs   

[Sean]

Jim, please post the make and model of your batteries and all the settings under menu #10.


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[rv_safetyman]

Sean, I will get the Trace information tomorrow - probably late as we have quite a bit going during the day.  The batteries are standard issue Sam's 6V golf cart.  I will see what the label says.

I started playing with this whole issue back in June.  I tried to chart time, SOC, specific gravity, etc.  One of my data sheets is almost toast due to battery acid

I would have to look at my notes, but it looks like I have settings in the TriMetric that are a bit conservative.  However, I am not impressed with the quality of my hydrometer.  The readings do not seem to agree with typical tables for SOC, but the relative numbers look somewhat realistic.

Jim

[rv_safetyman]

This morning, after 12 hours, it is up to 76%

The menu 10 main items are set at:

Bulk volts:  14.6
Absorption time 2:00
Float Volts:  13.5
Max charge amps AC:  20

I did not include the equalize and it does not appear that the temp comp is set. 

When I was playing with the system in June, I moved the temp. sensor out of the battery box to make sure it was not limiting the charge (the batteries were not at all hot at the time).

It looks like the settings are almost factory settings.  I do recall playing with them in June. 

I wonder about the 20 amp AC limit should be increased.  I have not played with that setting.  As I noted, I do use the input amperage quite a bit to reflect marginal 15 amp house circuits when we stay at relatives houses.

Jim

[Oonrahnjay]

(snip)  I do use the input amperage quite a bit to reflect marginal 15 amp house circuits when we stay at relatives houses. 

      Jim, what are your usual loads.  If you're pulling say 10 amps most of the time and you have the input limit set at 15, that wouldn't leave a lot for charging.  And if you consider you have efficiency losses, maybe a considerable fewer amp are actually through as charge.

      Your bulk and float voltages are actually a couple of tenths higher than mine and mine works OK, so I don't think that that's a big part of the problem.  Are you sure that all the batts are OK?

      (I don't have a Trace and my inverter/charger is a bit different - just some thoughts, I hope it's not a dumm-@ss distraction.)

BH   NC   USA

[TomC]

Jim-20amps isn't much. When I had 2-8D deep cycles, I just kept increasing my input amperage until I got a fault code on the inverter.  I then backed it off and that's where I had it for years-I believe it was around 50amps (12vdc).  With as many golf cart batteries as you have (the equal of 4-8D's) I would think you could increase your charge amperage to 80-100amps (12vdc).  This also sounds very elementary-but is all terminals clean?  Especially if you have watered batteries.

This is one good example of why I like AGM batteries.  In this case, Jim could still have the 8-6V batteries (even increase to the 400amp/hr/battery L16's if he has 18" height) and he could just increase the charge amperage up to the top of what the inverter puts out.  Just make sure the charge is not above 14.1 volts, and away you go!  Good Luck, TomC

[Sean]

...
Bulk volts:  14.6
Absorption time 2:00
Float Volts:  13.5
Max charge amps AC:  20
...

Jim, without the detailed battery information I can't say whether these settings are optimal.  There is a great deal of difference among GC2 batteries -- Sam's Club alone has at least three different models.  That said, I suspect your bulk setting is a bit low for flooded traction batteries.

One of the disadvantages of flooded golf car batteries is the charge acceptance rate.  Typical flooded GC2 batteries will be around 230 AH (20-hr rate), so your bank of eight would be around 920 AH.  Flooded batteries can typically be charged at C₂₀/5, which would be ~180 amps at 12vdc, or right around 20 amps of 120VAC at the charger, so that setting is likely correct.  Switching to AGM would let you charge at the maximum rate available from the Trace charger.

Frankly, I suspect your Tri-metric is wrong, rather than any problem with the batteries.  How often does the meter reset to "full"?  If it never gets there, the meter will accumulate more and more error over time.  This happens with our Link-10, even though we've dialed the settings in nearly perfectly.  In order to zero the meter error, we need to charge overnight on a shore service, causing the meter to reset.

-Sean
http://OurOdyssey.BlogSpot.com

[Sean]

Jim-20amps isn't much. ... I would think you could increase your charge amperage to 80-100amps (12vdc).

Tom, the SW series sets charge amperage at 120VAC.  So his "20 amp" setting is really around 180 amps at 12 VDC (after accounting for efficiency loss).

-Sean
http://OurOdyssey.BlogSpot.com

[bevans6]

I'm confused if the 20 amps is input to the batteries or 120VAC input to the inverter.  If it's to the inverter, that implies around 180 amps available to go to the batteries.  I have US-2200 batteries, so I have this generic charging instruction for all their batteries. They are fairly typical golf cart batteries, and I suspect these all follow a somewhat similar pattern.  

http://www.wholesalesolar.com/pdf.folder/battery-folder/charging_instruction_2011_2.pdf

They would have a bulk charge up to 14.4 volts at constant current with current equal to 10% of the 20 hour AH rating, then an absorption charge at 14.4 volts for 3 to 4 hours, then a finish charge for 2 - 3 hours at 15.3 volts current limited to 3% of the 20 hour AH rating, then going to the float charge at 13v forever.

Your bulk voltage sounds OK but one hour seems low, it would probably be closer to half the total time so 6 hours.  What is the absorption voltage?  The absorpion time could be longer.  And you have no finish charge - they call for slightly higher voltages and times with no finish charge.  Following these instructions the batteries are supposed to recharge in 12 hours or so.  Your original post suggests that you are programmed for a 1 hour bulk followed by 2 hours absorption, and then flip to float charge.

Brian

[Sean]

... Your bulk voltage sounds OK but one hour seems low, it would probably be closer to half the total time so 6 hours.  ...  Your original post suggests that you are programmed for a 1 hour bulk followed by 2 hours absorption, and then flip to float charge.

Brian, the SW does not have a bulk timer.  Bulk is a voltage setting, and the charger supplies the set current until the bulk voltage is reached.  At that point the absorption phase begins, where the bulk voltage is maintained for a set time.  This would be the one hour he mentions, although most deep cycle batteries really need two hours or so.  After that the charger switches to float.  More modern inverter/chargers have more sophisticated charge profiles.

-Sean
http://OurOdyssey.BlogSpot.com

[Sam 4106]

Hi Jim,

Based on the information in my Magnum Inverter manual, your absorb time should be 2 1/2 to 3 hours if the capacity of your batteries is in the 900 amp hrs range. Also that size battery bank can accept a lot more than 45 amps if your inverter will put out more than that. The voltage settings agree, within a 1/10 amp, so they should be OK. I think that if you increase both the absorb time and charger amps you will have much better results. Have you checked the voltage at the batteries when the charger is in absorb and float to see if they agree with the TriMetric readout? Have you tried resetting the TriMetric to see if the SOC reading changes?

Good luck, Sam

[rv_safetyman]

Lots of confusion about the amp/volt relationship I mentioned. Both the 20 and 45 amp settings are at 120 V.

Prior to this trip the bus sat on inverter charge and reached 100%.  I tried to find my TriMetric folder before I left this morning to verify the settings. Will also check battery info when I get home.

I am not concerned about the batteries or the inverter, just trying to get my head around what is going on.

In the past I have observed charge rates over 100 amps at 12V.  I will verify that later today by pulling the AC for a while and get the inverter back in bulk.

Thanks everyone for jumping in.

Jim

[Sam 4106]

Hi Jim,

Sorry I misunderstood that the 45 amps was the input to the inverter. I think I was confused because I don't think it is possible for your inverter/charger to draw that much with 12 volt output. I could be wrong. Are you sure you can set the bulk charge time? I can't with my Magnum. I can however set the absorb time according to the rating of the battery bank amp hrs. I think you should check the absorb time setting and increase it if your battery bank is rated at 900 amp hrs and the setting is 2 hrs as indicated. All bets are off if your batteries are not wired correctly. I suspect they are. Do you have a DC clamp on amp meter to verify that the TriMetric is reading correctly? Do you have a large 12 volt load on the batteries at the time you are trying to charge them? It seems to me that something is wrong since you're only getting from 64% SOC to 70% in 6 hours and then only to 76% after another 12 hours. I'm thinking that your charger isn't putting out it's rated capacity.

My thought is base on that I plugged in my inverter/charger this morning since the SOC on my batteries was 53%. I watched the gauge on the remote to see how long the charger stayed in bulk. It was only a minute or so before it went to absorb and the amps climbed to just over 90. About an hour and a half later the SOC was 76%. In 3 hours it was, in float, charging 10 amps and SOC was 83%. Now after 5 hrs the batteries are at full charge. I have a Magnum 4000 watt, 24 volt inverter and 6 group 27 deep cycle batteries that are 3 years old. The bank had 285 amp hrs rating at 24 volts when new. I realize that I have a smaller bank and it's capacity is somewhat less now I would guess.

Good luck, Sam

[rv_safetyman]

First, thanks to all for jumping in and giving me some new thoughts.  This is driving me crazy (or as Pat would say, crazier  ). 

I think I misspoke earlier (did not go back).  The bulk charge is not a time function, but the absorption is (two hours current setting).  One of the problems is that the Trace only shows LEDs for Bulk and Float.  Here is what the manual says about the bulk LED:

BULK (Yellow)
This indicator will be on to indicate the inverter is in the Bulk or Absorption charge stage. This indicator will
go off and the FLOAT indicator will illuminate when the battery voltage has been held near the SET BULK
VOLTS  DC  setting  for  the  time  period  determined  by  the  SET  ABSORPTION  TIME  setting  from  the
BATTERY CHARGING (10) menu heading.

That explanation confuses me.  Almost sounds like Bulk and Absorption is the same thing (?).  In any case, the absorption is set for 2 hours and I know that the yellow light does not stay on anywhere near that long.

Sam, your description of your charge rate is somewhat close to what I remember in the past.  It only took a few hours to get to 80-85% and then, of course, longer to finish out the full charge.

Here is where I am now.  At 4:00 PM (more than 24 hours) I was at 76%.  I checked the amperage and it was essentially a net 2 amps in and 13.3 volts (data per TriMetric).  I shut off the AC and with the fridge running (house type) the current was about 14 amps out.  I will leave the power off for a few hours and then turn on the AC and see what the charge rate is.  I will try to monitor it for a few hours to see how fast the charge amperage drops off.  Sam, your suggestion of a second DC ammeter is good.  I have a great clamp-on ammeter, but it is AC.  I found my 40+ year old ammeter that you use to straddle the cable. It has two sizes of notches and two scales.  One is 75 amps and the other is a few hundred amps.  Not a lab quality meter, but it should validate the TriMetric.

I suspect the TriMetric measures amperage pretty well.  It uses a shunt (should be reliable) and the amperage is a simple conversion of the voltage across the shunt.  Also, the draw for the fridge seems reasonable.

Will report tonight's testing later.  Tomorrow, I will add some testing with the hydrometer to see if I can correlate it to the TriMetric.  I did that in June, but have not had a chance to review my notes.  At the same time I will get better information on the batteries.

Jim