Two batteries in series, different specific gravity readings
Plowman
Solar Expert Posts: 203 ✭✭✭✭✭
I got two new Trojan T-105s 3 weeks ago or so, which I've been using every day since (I live off grid), recharged in part by one 158W solar panel and topped up with a Honda EB3500 with Iota 45.
Since I got the batteries the specific gravity was different. I thought this would even out as I used them, but it hasn't, the one battery is consistently lower than the other. Took a reading with a new hydrometer and got the same result. One battery was around 1.250, the other roughly 1.230. The hydrometer's built-in thermometer read 40 degrees but it was more like 55 outside. This is a significant difference, seems like a problem to me.
I'm using cheapo auto parts store hydrometers, my old one (one of these) measured the stronger battery at around 1.30, which is obviously wrong. The new one is one of these and appears to work much better.
Since I got the batteries the specific gravity was different. I thought this would even out as I used them, but it hasn't, the one battery is consistently lower than the other. Took a reading with a new hydrometer and got the same result. One battery was around 1.250, the other roughly 1.230. The hydrometer's built-in thermometer read 40 degrees but it was more like 55 outside. This is a significant difference, seems like a problem to me.
I'm using cheapo auto parts store hydrometers, my old one (one of these) measured the stronger battery at around 1.30, which is obviously wrong. The new one is one of these and appears to work much better.
Comments
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Re: Two batteries in series, different specific gravity readings
You need to equalize those batteries. For one thing they both appear to be too low. For another they are not balanced.
The quality of the hydrometer is not so much of an issue if you start with known fully charged and equal batteries, and then compared subsequent readings to that baseline. -
Re: Two batteries in series, different specific gravity readingsI got two new Trojan T-105s 3 weeks ago or so, which I've been using every day since (I live off grid), recharged in part by one 158W solar panel and topped up with a Honda EB3500 with Iota 45.
I agree with Carriboocoot's comments, and noticed another thing. You'd be better off bulk charging your batteries early in the morning with the generator, then allowing the sun to take over for the rest of the day to finish the charge. The batteries are NOT being fully charged, one worse than the other, and they must be fully charged before you can begin the EQ process. EQ is a controlled overcharge process that brings all cells to the same level, and you cannot overcharge a battery, controlled or not, unless the battery bank is first fully charged. -
Re: Two batteries in series, different specific gravity readings
I wasn't too worried about the SOC, I expected them to be down given how much juice I've been using and the cloudy/rainy conditions, plus my crap charge controller (which I described in my earlier thread).Cariboocoot wrote: »You need to equalize those batteries. For one thing they both appear to be too low. For another they are not balanced.
But I am worried about the imbalance. I charged them for 2.5 hours or so this afternoon with my generator and Iota. Had 14.7V for a while, then went down to ~14.15 where it stayed until I shut the gennie down. Do I need to run it longer? I've run it for 3-3.5 hours with these batteries on at least two or three occasions, never see the voltage drop below 14.1 or so.
Apparently Iotas only equalize if they've been sitting on float for a week (from this page). I've never seen the Iota put out more than 14.7 or 14.8V when run on my generator; I obviously can't run it for a week straight. And there are no manual settings. Maybe wait for my new Morningstar TS-45 to come in the mail and pray for sun? I think I can figure out how to manually equalize with that, but I only have the one 158W panel.
My previous battery was AGM, so this hydrometer thing is new to me. I checked with my new hydrometer after charging and it said the batts were still at 1.250 and 1.225. Now I'm thinking the new hydrometer may not work.The quality of the hydrometer is not so much of an issue if you start with known fully charged and equal batteries, and then compared subsequent readings to that baseline.
The old hydrometer still said the stronger battery was at 1.300. It isn't stuck at this position, it's shown the batteries drawn down in the past when I expected them to be down. Maybe it was right in the beginning and the batteries were full. But it still leaves the problem of the unbalanced batteries.
Is there a hydrometer that you can recommend that is accurate and doesn't dribble all over the place? -
Re: Two batteries in series, different specific gravity readings
See what Wayne said about Bulking with the gen & Iota and using the panel & controller to finish charge. Also the panel may be used for EQ as that does not require high current but rather higher (than Absorb) Voltage.
14.7 Volts is actually slightly less than Trojan calls for, and it won't be temp compensated so it might actually be slightly higher. Also we don't know if it is staying in Absorb long enough. Shutting down the Iota when Voltage drops to 14.15 (Float setting?) and restarting it for another cycle might help.
All hydrometers are a pain, but necessary. I actually use a cheap $5 one but I'm practiced at interpreting what I see. -
Re: Two batteries in series, different specific gravity readings
The IOTA chargers come in two flavors : with built on IQ-4 and without, that uses the plug in Module. The Standard without IQ-4 can have the output adjusted to use for Equalize charging. You have to open the charger and adjust the output, there is a 10 turn potentiometer on the fan end that adjusts the Output. You have to plug in the Hi Voltage adapter in the Jack and you can raise the output to 15.3 V or so on the output. You can then set it back when your done.
You might be able to adjust the one with IQ-4 built in using the same procedure , but I never tried it.
At 1.230 you could expect it to take 6-8 hours on more to raise the SG level to 1.265 -
Re: Two batteries in series, different specific gravity readings
I have one that originally didn't come with IQ-4 (I added an with an external IQ-4 unit). I'll have to crack it open.Blackcherry04 wrote: »The IOTA chargers come in two flavors : with built on IQ-4 and without, that uses the plug in Module. The Standard without IQ-4 can have the output adjusted to use for Equalize charging. You have to open the charger and adjust the output, there is a 10 turn potentiometer on the fan end that adjusts the Output. You have to plug in the Hi Voltage adapter in the Jack and you can raise the output to 15.3 V or so on the output. You can then set it back when your done.
You might be able to adjust the one with IQ-4 built in using the same procedure , but I never tried it.
Yikes, that's a long time to run the gennie---and that's after I adjust the Iota?At 1.230 you could expect it to take 6-8 hours on more to raise the SG level to 1.265
I'll try running it at night (don't have time to run it in the morning before work) and see if I can't manually program my cheapo controller to go into equalization mode---supposed to be sunny this week. My new controller isn't scheduled for delivery for another week or so. -
Re: Two batteries in series, different specific gravity readings
You don't have to do it all at one time, do it over a couple days. It depends on how hard the sulfate is, if it's just a charge problem, they'll come up faster. I do have concern where there is .30 disparity in the two batteries, ideally you have a charging source where you could bring the lower battery up to the level of the higher one first @ 7.75 volts, then finish them together. T -105's are predictable, once you see how they are responding.I have one that originally didn't come with IQ-4 (I added an with an external IQ-4 unit). I'll have to crack it open.
Yikes, that's a long time to run the gennie---and that's after I adjust the Iota?
I'll try running it at night (don't have time to run it in the morning before work) and see if I can't manually program my cheapo controller to go into equalization mode---supposed to be sunny this week. My new controller isn't scheduled for delivery for another week or so.
The potentiometers I have seen in them are blue or white and have a small silver adjusting screw for a small screwdriver. -
Re: Two batteries in series, different specific gravity readingsYikes, that's a long time to run the gennie---
And THAT sir is why we recommend fully bulking your batteries with the generator early in the morning, then letting the sun finish the job during the rest of the day. -
Re: Two batteries in series, different specific gravity readingsI have one that originally didn't come with IQ-4 (I added an with an external IQ-4 unit). I'll have to crack it open.
Yikes, that's a long time to run the gennie---and that's after I adjust the Iota?
I'll try running it at night (don't have time to run it in the morning before work) and see if I can't manually program my cheapo controller to go into equalization mode---supposed to be sunny this week. My new controller isn't scheduled for delivery for another week or so.
In my opinion, the external IQ4 should only be used if you plan to have the generator running for a LONG time to power other loads just so that you don't run too long of an absorb with the Iota. I almost never used mine. Just crank up the voltage with that POT inside it (WITH the rj45 jack inserted) and always charge (bulk/absorb) with the jack in. I never used the Iota with the jack out because that was basically float voltage and it is not smart enough to absorb until 'done" - it just absorbs for (i believe) 4 hours and then drops to float regardless of it the batteries are actually fully absorbed.
If you end up running the generator for extended times, then go ahead and plug the IQ4 in AFTER it has charged (fully).Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html -
Re: Two batteries in series, different specific gravity readings
Input from a rookie!! Trials and tribulations with my system when new, were getting batteries properly charged. I went through a couple of months of no sun to speak of, which created a very frustrating lesson on generaters and chargers. I figured out that my chargers were the problem, one a digital car battery charger and the other a built in on an old Trace inverter. Conventional chargers rely on battery voltage to avoid overcharging, the problem I had was they would drastically drop amperage quite quickly, which causes Very long charge times. I also realized that voltage readings tell you nothing useful!!! unless batts are stagnant for a long period, which does not happen conveiently on your system. I asked about Iota chargers on here and may buy one for next winter, but doesn't sound like they can be controlled as well as a good solar charger. Therefor the recommendation to bulk with gen. then finish with solar is to be heeded! I would however question the 158watt panel?? should be able to hold absorb BUT you still need to get there by confirming SG. I found when I finally got 1.265 SG getting back there was easy. I also found out how long I needed to be in absorb to get to 1.265! very important! The other frustration was learning about hydrometers, anything with friction between the body and measuring device should be left to someone with way more patience than yours truly
) The antifreeze style is better as far as moving to the proper position, however the graduations are useless for acurate reading IMHO. I purchased a Hydro-volt and will never look back. I now go only by SG to determine SOC, 4x240w panels,Classic 150 CC, 4x380AHR L16's, antique Trace 12V inverter -
Re: Two batteries in series, different specific gravity readings
Okey dokey, after work today I cracked open the Iota and found the potentiometer. Unplugged the IQ4 and plugged in the dual voltage jack. Fired up the gennie and got the voltage to ~15.5 per Trojan specs (Watts Up says it's 15.54V, my multimeter says it's 15.47V, not sure which is more accurate). Yay!
Blackcherry, thanks for your post on how to do this. For other newbies out there, my potentiometer was blue and has “Boshen 3266” stamped on it. It's located near the fan and has a tiny little screw on top of it. Turning it left increased the voltage---doesn't take much turning to make big changes, so go slowly.
I plugged in the IQ4 just to see what would happen and the voltage jumped to 15.9V and was still climbing before I unplugged it and put the other jack back in. With neither the dual voltage jack or IQ4 the voltage is 14.97 as measured with the Watts Up---I was hoping it would be 14.8V, but that would be too easy.
I'm going to let the gennie run for as long as possible, filled the tank and started it at 6pm, will have to turn it off when I go to bed around 10:30.
I also adjusted my cheapo Chinese charge controller to its highest voltage, 0.9V above the default (which is allegedly 14.4V but I've never seen it go above ~14.15V). I didn't notice any jump in voltage when I did this, but it's hazy out and the sun was starting to get low. I don't have confidence in this controller, looking forward to getting my new Morningstar in the mail. -
Re: Two batteries in series, different specific gravity readings
Thanks for the Hydro-volt mention, hadn't heard of those. It's on my list of stuff to get. I take it you like it? Does it dribble at all?Input from a rookie!! Trials and tribulations with my system when new, were getting batteries properly charged. I went through a couple of months of no sun to speak of, which created a very frustrating lesson on generaters and chargers. I figured out that my chargers were the problem, one a digital car battery charger and the other a built in on an old Trace inverter. Conventional chargers rely on battery voltage to avoid overcharging, the problem I had was they would drastically drop amperage quite quickly, which causes Very long charge times. I also realized that voltage readings tell you nothing useful!!! unless batts are stagnant for a long period, which does not happen conveiently on your system. I asked about Iota chargers on here and may buy one for next winter, but doesn't sound like they can be controlled as well as a good solar charger. Therefor the recommendation to bulk with gen. then finish with solar is to be heeded! I would however question the 158watt panel?? should be able to hold absorb BUT you still need to get there by confirming SG. I found when I finally got 1.265 SG getting back there was easy. I also found out how long I needed to be in absorb to get to 1.265! very important! The other frustration was learning about hydrometers, anything with friction between the body and measuring device should be left to someone with way more patience than yours truly) The antifreeze style is better as far as moving to the proper position, however the graduations are useless for acurate reading IMHO. I purchased a Hydro-volt and will never look back. I now go only by SG to determine SOC,
I'm trying to heed the advice of bulking with the gennie and finishing with solar, but equalizing is the highest priority given the battery imbalance. Thanks to the advice here I figured out how to manually equalize with the Iota. -
Re: Two batteries in series, different specific gravity readings
Dang it, I just reread your post and ran out to adjust the Iota's voltage down to 14.8. Hopefully 1.5 hours of 15.5V won't hurt a battery at ~65%.waynefromnscanada wrote: »they must be fully charged before you can begin the EQ process. EQ is a controlled overcharge process that brings all cells to the same level, and you cannot overcharge a battery, controlled or not, unless the battery bank is first fully charged. -
Re: Two batteries in series, different specific gravity readings
It won't hurt them, no one can tell you where that Full Charge thing came from or why. One reason would be that you cannot check the SG level without having a Full Charge and you already know they are low. It's like most things on the internet, it's copy and pasted often and repeated over and over. Heart Interface always had it built into their Inverter / Charger scheme, they also had a 8 hour automatic EQ. Xanterx kept the automatic recharge and full charge and cut the time to a hour at a time. Trace always had a hour, Magnum has 4 hours.Dang it, I just reread your post and ran out to adjust the Iota's voltage down to 14.8. Hopefully 1.5 hours of 15.5V won't hurt a battery at ~65%.
One reason to do a full charge the DAY before you start to do a EQ is heat, depending on it's length you could expect anywhere from a 20-30 deg rise in battery temperature, if you use the 115 Degree limit, you can get there fast. Pushing the over voltage to 15.5 V takes more current, but once you get ether that will lower as it's absorbed and the batteries will begin to reject it and you'll see a drop.
. -
Re: Two batteries in series, different specific gravity readingsBlackcherry04 wrote: »It won't hurt them, no one can tell you where that Full Charge thing came from or why.
.
Actually, what it means, is that the batteries will not begin to EQ until they are fully changed.
In other words, until they are fully charged, you're not doing an EQ, you're just charging them. -
Re: Two batteries in series, different specific gravity readings
Equalizing is "over charging" some cells to get the "excess current" through those fully charged cells to bring the "weak cells" backup to full charge too (i.e., you are gassing the "full charge cells" to recharge the lower charged cells).
That is why equalization is "hard" on a battery bank and you (usually) only want to do it when needed (different battery vendors do have different equalization suggestions).
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
Re: Two batteries in series, different specific gravity readings
Very true, it's hard enough cell to cell when one is much lower than the others. In this case with new batteries, I'd like to see the lower one brought up to the one showing higher SG's. Ideally EQ'd by it's self until it rises to that level. In the real world without the correct equipment, I'd tie it to a old junk battery and bring it up.Equalizing is "over charging" some cells to get the "excess current" through those fully charged cells to bring the "weak cells" backup to full charge too (i.e., you are gassing the "full charge cells" to recharge the lower charged cells).
That is why equalization is "hard" on a battery bank and you (usually) only want to do it when needed (different battery vendors do have different equalization suggestions).
-Bill -
Re: Two batteries in series, different specific gravity readings
One would assume, but it's ofter not stated that way and I see posters say they had to run their Generator for 5 hours to get a Full Charge ( Bulk / Absorb / Float ) before they started a EQ for another 6-8 hours of EQ voltage, not that it's going to hurt anything, but it does add to the heating and thats never good.waynefromnscanada wrote: »Actually, what it means, is that the batteries will not begin to EQ until they are fully changed.
In other words, until they are fully charged, you're not doing an EQ, you're just charging them. -
Re: Two batteries in series, different specific gravity readings
I ran the gennie for ~4.5 hours last night, first 1.5 hours at 15.5V (as I described above), the last 3 hours at 14.8V.
Had good sun today for the first time in a couple weeks, my cheapo charge controller was up in the 14.8ish range for the first time ever, controller showed the batteries as full when I checked on it after work and was quickly cycling between 0 amps and 1-3 amps or so. So adjusting the maximum voltage on the thing did appear to work.
I'm currently equalizing at 15.5V with the gennie. When I started the strong battery had a SG of 1.28, the weak one was at 1.26 (~40F). After an hour the strong battery seems a bit up but the weak battery is the same. This is measured with my new float hydrometer, which does appear to work, but I really don't like it, kind of a PITA to use and to get a consistent reading. -
Re: Two batteries in series, different specific gravity readings
Your at decision time. As you can see it was more a charging issue than sulfate because the higher came up with very little effort. It's not good to keep on over charging it to bring the second one up. Now you have a hydrometer you can trust the reading from. I'd take the lower one to someone with the equipment to Equalize it or find a old junk 6v battery to put it into series with so you can hammer it with to bring it up. The other side of the coin, is you can live with it and have some diminished capacity. 1.260 is not that bad, it's the differential between the two that will always be there as they charge and discharge. You can watch them for a week and see how they even out, they will somewhat as the overcharge drops on the higher one.
With new batteries, it's not that unusual to have one a little stronger than the other and they will accept a charge a little different and have different SG's, I have a new set that I have been battling with myself that I just cannot keep them at the same SG level. -
Re: Two batteries in series, different specific gravity readings
Another possibility is to put a substantial 6 volt load of some sort on the "good" battery only, while doing the EQ. That could prevent excess overcharging of the "good" one. Of course a close eye would have to be kept on things. -
Re: Two batteries in series, different specific gravity readings
Get an 6 volt head light and clip it across the "good 6 volt battery" (or 12 volt lamp across 12 volt batteries in 24/48 volt systems)--Be careful of sparks... Charging batteries have lots of hydrogen in the area and you don't want to cause and explosion when connecting up the bypass load.
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
Re: Two batteries in series, different specific gravity readings
As far as I know I don't have anything that's 6V, and the only dead batteries sitting around the farm are 12V. I'll keep my eye out for something that might work.
No change in the batts, just checked them, the one is still at 1.28, the other still at 1.26 (temp was ~60F). I ended up equalizing them for something like 3 hours yesterday. I think I'll give them a week before I check again, compulsively checking SG is getting tiresome. Don't think I'll equalize again for another month or so unless y'all think it's advised.
On the up side, I got my new Morningstar TS-45 in the mail today The first step towards expanding my system. Now I just need to shell out for two more panels. -
Re: Two batteries in series, different specific gravity readings
Try a golf course or Golf Cart supply they usually have some old ones this time of the year waiting for pick-up. All you need to do is use it for a day and take it back. -
Re: Two batteries in series, different specific gravity readings
Update:
The two batteries have come closer, still not completely equal, but closer.
Checked SG this afternoon after equalizing (with solar) for an hour or so. The SG of the cells in the "strong battery" averaged 1.285. The SG of the cells in the "weak battery" averaged 1.280. This is measured with a different hydrometer than I was using at the beginning of the thread. I'm using a Hydro-Volt, which I really like.
So it appears the weak battery is finally catching up. -
Re: Two batteries in series, different specific gravity readings
Don't drive yourself nuts trying to get them exactly equal... If they are within 0.015 to 0.030 SG or better of each other--That is not bad.
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
Re: Two batteries in series, different specific gravity readings
It might be easier to spend $50 on a battery bank equalizer. But I don't know if one intended for 12/24V works at 6/12V.I am available for custom hardware/firmware development
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Re: Two batteries in series, different specific gravity readingsDon't drive yourself nuts trying to get them exactly equal... If they are within 0.015 to 0.030 SG or better of each other--That is not bad.
-Bill
So you're saying I shouldn't stay up tonight worrying the 0.01 difference between the cells in my batteries? Good to know, I had planned on sleeping in the trailer where I keep my batteries, whispering them sweet nothings all night.
Trojan says to equalize when difference is +/- 0.015. Thanks for making me look that up.
I think sometimes I tend to obsess too much about the little things. Meanwhile, the big things fly right by my head without notice.
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