Specific Gravity Discrepancies

[Keajre]

Dear Friends,

 

 Earlier in the year I installed four T145 Trojan wet lead acid batteries.  Absolutely delighted with them.  Once every three months or so I take a reading of the specific gravity. 

 

 I have noticed for two readings in a row  (over 6 months)  that one of the four batteries in the bank has a specific gravity reading Of 0.010 less than the others. Three of the four batteries measure 1.290 when fully charged.  The third reads 1.280 for all three cells (6v batteries).  I was reading that if the discrepancy gets to 0.020 then the batteries become on unserviceable.

 

 I do conduct occasional equalisation charges although I never reach the recommended 16.2 Volts.  Actually only manage about 15.2 which is under what Trojan recommend.  Attached is the wiring diagram .  Is the battery closest to the inverter that is reading less.

 

SoC never goes below 70% (30% DoD).

 

 Little concerned and just wants to get some feedback from you guys 

 

Kind Regards

 

Stuart

[nicknorman]

Are you compensating for temperature correctly? The original sg is 1.277. The sg can change quite a bit with the electrolyte level so are the batteries a bit down on the correct level (which is 1/8” or 3mm below the well in the filler)?

 

All that said I don’t think 0.010 is anything to worry about, more likely a difference in temperature or electrolyte level.

 

And no, 0.020 down doesn’t indicate impending death!

 

15.2v in cold weather is closer to a normal finishing charge than an equalising charge! But should be ok in summer.

 

(edited because I got my hot and cold confused)!

Edited July 22, 2018 by nicknorman

[Richard10002]

7 minutes ago, nicknorman said:

15.2v in hot weather is closer to a normal finishing charge than an equalising charge!

And how the ordinary person with ordinary equipment can ever get the voltage as high as 16.2V, as per Trojan recommendations, is anybodys guess.

 

The only way I have seen suggested here is to have a "bench power supply", which is not something that (m)any of us are likely to have.

 

With Sterling chargers, I can get to 15.5V, and havent found any normal equipment that goes higher.

[nicknorman]

Just now, Richard10002 said:

And how the ordinary person with ordinary equipment can ever get the voltage as high as 16.2V, as per Trojan recommendations, is anybodys guess.

 

The only way I have seen suggested here is to have a "bench power supply", which is not something that (m)any of us are likely to have.

 

With Sterling chargers, I can get to 15.5V, and havent found any normal equipment that goes higher.

Our Mastervolt Combi goes to 16v. But I find 15.5v is plenty. In the summer I don’t equalise, in the winter even with cold batteries 15.5v is OK.

[MtB]

6 minutes ago, Richard10002 said:

With Sterling chargers, I can get to 15.5V, and havent found any normal equipment that goes higher.

 

I'm fairly sure I was able to set the equalising charge voltage on my Tracer solar controller to something close to 32v.

[Keajre]

57 minutes ago, nicknorman said:

Are you compensating for temperature correctly? The original sg is 1.277. The sg can change quite a bit with the electrolyte level so are the batteries a bit down on the correct level (which is 1/8” or 3mm below the well in the filler)?

 

All that said I don’t think 0.010 is anything to worry about, more likely a difference in temperature or electrolyte level.

 

And no, 0.020 down doesn’t indicate impending death!

 

15.2v in cold weather is closer to a normal finishing charge than an equalising charge! But should be ok in summer.

 

(edited because I got my hot and cold confused)!

Hello Again,

 

These figures aren’t temp compensated no.  I just checked.  The battery which reads lower is 2 degrees colder.  It also has less electrolyte in the cell tank.  Not sure how it’s possible to measure 3mm from below the well.  Any tips?  I’g Guess it was about 5-10 mm gap that battery (still well about the lead plates).  The others are about 4-6 mm.  I had no idea that difference would make such a difference.  

 

The thing is, 3 months ago I topped them all up.  Tried to do the 3mm thing by eye back then.  Again, that same battery is lower in electrolyte than the rest.  My theory, two things.  A) its gassing more that the others due to its position. b ) it’s gassing more because its connected to the negetive lead.  

 

Probably got that wrong, but cant think of any other reason why.  All negs inc earth flow through that battery 1st.  Coudl that cause it?  Should I rotate them?  Just the 1st and last battery?

53 minutes ago, Richard10002 said:

And how the ordinary person with ordinary equipment can ever get the voltage as high as 16.2V, as per Trojan recommendations, is anybodys guess.

 

The only way I have seen suggested here is to have a "bench power supply", which is not something that (m)any of us are likely to have.

 

With Sterling chargers, I can get to 15.5V, and havent found any normal equipment that goes higher.

Good to know its not just me scratching my head on this one.  I think with Victron MultiPlus I could temporarily increase the absorb voltage.  The equalisation cycle just adds 1 volts (or similar). Not sure if it really matters.,  Like you say depends on the temperature I guess.  The Victron is setup to temperature compensate when it charges (or draws)

46 minutes ago, Mike the Boilerman said:

 

I'm fairly sure I was able to set the equalising charge voltage on my Tracer solar controller to something close to 32v.

32v, get them bubbling like a witches couldren lol 

[MtB]

7 minutes ago, Keajre said:

32v, get them bubbling like a witches couldren lol

 

You seem bright enough to have deduced from my comment I have a 24v battery bank, and 32v for me is the equivalent of 16v for you. 

 

But maybe I am wrong!

 

Lol!

[nicknorman]

You are talking about fairly small differences in level which would make a fairly small difference in sg. But those batteries hold a lot of electrolyte above the plates (when at the correct fill level) so there can be quite a difference between just covering the plates, and full to the correct level.

 

so a few points: reference temperature is 27C. What temperature were your batteries when you measured? The note below shows how to compensate for temperature. It also mentions that a variation or more than 0.050 is the time to start doing something - you are way below that!

 

 

Your wiring diagram looks fine. There isn’t a fundamental reason why there is a difference other than manufacturing tolerances. I have 4 x T105s and do find there is sometimes a slight voltage difference between two batteries in series, but I don’t have a clever answer as to why.

 

Couldmthe one battery be nearer a heat source from the engine?

 

But yes if it’s worrying you, why not rotate the batteries and see if the issue follows the battery or the location?

 

As for filling, I just eyeball it, not that critical. I tend to use wooden skewer to prod the level, which makes it easier to see.

 

Edited July 22, 2018 by nicknorman

[Keajre]

19 minutes ago, Mike the Boilerman said:

 

You seem bright enough to have deduced from my comment I have a 24v battery bank, and 32v for me is the equivalent of 16v for you. 

 

But maybe I am wrong!

 

Lol!

Yes it was a poor attempt at humour ?

[Keajre]

15 minutes ago, nicknorman said:

You are talking about fairly small differences in level which would make a fairly small difference in sg. But those batteries hold a lot of electrolyte above the plates (when at the correct fill level) so there can be quite a difference between just covering the plates, and full to the correct level.

 

so a few points: reference temperature is 27C. What temperature were your batteries when you measured? The note below shows how to compensate for temperature. It also mentions that a variation or more than 0.050 is the time to start doing something - you are way below that!

 

 

Your wiring diagram looks fine. There isn’t a fundamental reason why there is a difference other than manufacturing tolerances. I have 4 x T105s and do find there is sometimes a slight voltage difference between two batteries in series, but I don’t have a clever answer as to why.

 

Couldmthe one battery be nearer a heat source from the engine?

 

But yes if it’s worrying you, why not rotate the batteries and see if the issue follows the battery or the location?

 

As for filling, I just eyeball it, not that critical. I tend to use wooden skewer to prod the level, which makes it easier to see.

 

 

I only took temp from one of the batteries at the time of sampling, was 28 degrees.  So the compensation would be negligible.  Although the lower battery was 2 degrees colder, so 26.  Still would such a tiny compensation.  

 

Thanks for pulling out the part of the manual which relates to this.  That’s good to know, 0.010 isn’t a concern then.  I’m overreacting.  Just wanted to check, spent a lot of money on the buggers, want to take care of them.  

 

That battery is furthest from the engine. Pic attached (its the battery behind the Blue MPPT regulator).  

 

Thanks for filling tips.  I might try and trick the Victron Multi-Plus into delivering a correct equalisation charge and swap them around too,  but no urgency it would seem.

 

 

[nicknorman]

Could heat generated by the MPPT possibly be an issue? (I don’t know how hot they get, but there’s plenty of finning).

 

Is one of those visible busbars carrying the positive? If so I’d say that is asking for an accident and probably a BSS fail. Try to fit a cover over it so some random interaction with a spanner, windlass etc - or worse, a metal watch strap, neck chain - doesn’t cause 1000s of amps to flow out of the batteries and melt stuff!

[MtB]

47 minutes ago, Keajre said:

The thing is, 3 months ago I topped them all up.  Tried to do the 3mm thing by eye back then.

 

I'd be inclined to think Trojan's intention is top them up exactly to the level indicator, then they are slightly over-filled (by 3mm) and as the water slowly gets converted and vanishes, the level falls to correct then to a little low in the period until you check them again

[Keajre]

7 minutes ago, nicknorman said:

Could heat generated by the MPPT possibly be an issue? (I don’t know how hot they get, but there’s plenty of finning).

 

Is one of those visible busbars carrying the positive? If so I’d say that is asking for an accident and probably a BSS fail. Try to fit a cover over it so some random interaction with a spanner, windlass etc - or worse, a metal watch strap, neck chain - doesn’t cause 1000s of amps to flow out of the batteries and melt stuff!

MPPT generates very little heat.

 

yes I have the busbar covers, just need to adapt them and fit them. Been on my todo list for a while. This reminds me, thanks

[Keajre]

 I’m using a refractometer instead of a hydrometer.  So much easier, I’ll never go back 

[nicknorman]

12 minutes ago, Keajre said:

 I’m using a refractometer instead of a hydrometer.  So much easier, I’ll never go back 

I agree! The gravities as measured do seem a little high though, do you do a calibration/adjustment of the refractometer with a drop of pure water from time to time?

[MtB]

4 minutes ago, nicknorman said:

I agree! The gravities as measured do seem a little high though, do you do a calibration/adjustment of the refractometer with a drop of pure water from time to time?

 

The level make a LOT of difference to the SG.

 

My Yuasa Trojanoids are about 1/2" low but the plates are still well covered. The SG is bang on at 1.277 but the capacity is down to 50% of badge. So I'm pretty sure if I toppede them up to the mark, the SG would fall dramatically given the high degree of suplhation.

[Keajre]

36 minutes ago, nicknorman said:

I agree! The gravities as measured do seem a little high though, do you do a calibration/adjustment of the refractometer with a drop of pure water from time to time?

It goes up to 1.30 sometimes afyer equalisation. Yes i did a calibration with distilled water. Not sure why the readings are so high. They are very new batteries

[MtB]

2 minutes ago, Keajre said:

It goes up to 1.30 sometimes afyer equalisation. Yes i did a calibration with distilled water. Not sure why the readings are so high. They are very new batteries

 

It is because they are not topped up to the correct level. 

[Keajre]

1 minute ago, Mike the Boilerman said:

 

It is because they are not topped up to the correct level. 

Ah ok, makes sense, I’ll top them up and re-check after a couple of days, thanks

36 minutes ago, Mike the Boilerman said:

 

The level make a LOT of difference to the SG.

 

My Yuasa Trojanoids are about 1/2" low but the plates are still well covered. The SG is bang on at 1.277 but the capacity is down to 50% of badge. So I'm pretty sure if I toppede them up to the mark, the SG would fall dramatically given the high degree of suplhation.

I didnt know that. Thanks for sharing

[MtB]

Just now, Keajre said:

Ah ok, makes sense, I’ll top them up and re-check after a couple of days, thanks

 

Yes my experience outlined in post 16 suggests the SG is very sensitive to the degree of dilution.

[Keajre]

Just now, Mike the Boilerman said:

 

Yes my experience outlined in post 16 suggests the SG is very sensitive to the degree of dilution.

I always wondered. Assumed the sulphuric acid would reach the same amount eventually. So if it has a significant impact on SG readings, why doesnt it also have an impact on voltage?  I have books I keep meaning to read about the deeper side of battery chemistry 

[MtB]

3 minutes ago, Keajre said:

So if it has a significant impact on SG readings, why doesnt it also have an impact on voltage?

 

And capacity too, I wonder. 

 

Can't answer your question. The more I learn about batteries the less I find I know.

 

Another possible variation is the strength of the acid added when they are first sold. I'm suspect they are shipped dry and the acid added on the bench locally by the distributor. And I suspect sulphuric acid is a LOT more expensive than distilled water so there must be a temptation for an unscrupulous distributor to send them out with a bit of distilled mixed in.... who would notice!

[nicknorman]

24 minutes ago, Keajre said:

I always wondered. Assumed the sulphuric acid would reach the same amount eventually. So if it has a significant impact on SG readings, why doesnt it also have an impact on voltage?  I have books I keep meaning to read about the deeper side of battery chemistry 

The amount of sulphuric acid in a (fully charged and unsulphated) battery remains constant. Only the water gasses off, increasing the strength of the electrolyte (and hence the sg), water is then added again periodically to bring the level up and the acid concentration and hence sg back to standard.

The electrolyte strength does have a slight impact on voltage, it is a little higher for a given SoC if the level is reduced due to loss of water and hence the acid is stronger.

[WotEver]

10 hours ago, Richard10002 said:

And how the ordinary person with ordinary equipment can ever get the voltage as high as 16.2V, as per Trojan recommendations, is anybodys guess.

Two ways that I’m aware of (well three if you include the bench psu idea):

 

1. Many solar controllers can do it. 

2. A buck/boost converter such as https://m.ebay.co.uk/itm/DC-DC-Converter-10-12-15-20A-150-250-300-400-1200W-Step-up-Step-down-Buck-Boost/192298255711?hash=item2cc5de855f%3Am%3AmHy5fhZloIDZTHImuC1ILHQ&var=492234936334&_sacat=0&_nkw=buck+boost+converter&_from=R40&rt=nc&_trksid=p2380057.m4084.l1311.R1.TR6.TRC1.A0.H0.Xbuck+boost.TRS0

[Richard10002]

I’m fairly confident with electrics, but wouldn’t know where to start with a buck boost converter... presumably it needs fitting between charger and batteries, some kind of switch to put it in the circuit or out of it, a nice box, and so on... so quite a job for the ordinary boater. 

 

Ditto the bench psu. I wouldn’t know what to buy, how to connect it, and it looks like a bit of a faff.

 

My tracer solar controller seems to have an equalisation setting, but I think it runs it every 28 days, rather than when I choose. I can set it to run for a max of 3 hours, and it might be settable to 16 volts ; but what if there’s no sun when you want to Equalise?

 

You might ythink I’m picking holes or being petty, but I have genuinely considered a bench psu for my previous Trojans, and a buck boost to get 14v for a TV, and dismissed both as they seem too complicated and a faff.