Electrolyte specific gravity anyone?

[Loafer]

i'm studying me 4 new T105 batteries, wired series-parallel for 12V at 450Ah and only a month old.

 

Every couple of days of use, or 3 at most, I recharge them until the tail current drops to about 5A, which (according to Trojan) is 100% charged. (1-3% of 20hr capacity (450Ah) on their charge curves). That can take most of the day.

 

My Victron BMV600S monitor reckons I'm 100% 'SOC' way before that, but I'm ignoring that for now, in order to comply thoroughly with Trojan's recommendations. So, for the moment, I am only regarding tail current at (14.8V) as a measure of SOC.

 

Meanwhile, I also have a boggo '110' as a start battery, which is not charged unless the engine is running, and not monitored.

 

Just now, at 5A charging current, I checked a few cells in the T105s with a hydrometer from Halfords. It has SG readings, along with 3 colour zones: red, white and green, according to perceived wisdom.

 

I can't read the numbers, but I don't think it's relevant here, but I know what they should be.

 

Ok here's the thing:

 

Even with that Trojan-recommended tail current achieved, I still can't get the hydrometer to get nicely into the green. It is hovering just at the border with the white.

 

The 5-year old start battery however, shows SG comfortably in the green.

 

Can anyone start to tell me why?

 

ETA They're never discharged below about 75%

Edited January 31, 2015 by Loafer

[dmr]

You are most likely not charging the Trojans quite as much as you think and now have some sulphation.

You need to have some means of doing an equalisation charge (15.5volts), this will sort them out (I was going to say this'll fix it but that phrase is non PC these days!).

Don't worry so much about the 100% charge every other day, Trojans can take some abuse, a full charge once a week, or even less, will be fine as long as you can equalise once every month or two.

If you have sulphation the capacity (and SG) just settles at a lower level so the battery shows the outward signs (tail current) of full charge but its not.

SG should be similar to your starter battery, and the "green" SG of your starter confirms that your hydrometer is OKish

Don't worry, after only a month you can easily sort this out.

 

I suspect Trojans actually enjoy a really good discharge once in a while,.... take them down to 30!

 

.............Dave

[Boredrider]

I bought one of those Halfords things when I bought my T105s a couple of years ago. I couldn't get on with it, and ended up buying a refractometer off ebay. Like this http://www.ebay.co.uk/itm/RHA-100ATC-Ethylene-Propylene-Glycol-Antifreeze-Refractometer-Tester-Battery-/291126071884

 

I find the refractometer much more accurate and informative, and the Halfords device has been consigned to the depths of the tool locker.

 

Yesterday's checks gave readings between 1.30 and 1.28 across the bank.

[Loafer]

I bought one of those Halfords things when I bought my T105s a couple of years ago. I couldn't get on with it, and ended up buying a refractometer off ebay. Like this http://www.ebay.co.uk/itm/RHA-100ATC-Ethylene-Propylene-Glycol-Antifreeze-Refractometer-Tester-Battery-/291126071884

 

I find the refractometer much more accurate and informative, and the Halfords device has been consigned to the depths of the tool locker.

 

Yesterday's checks gave readings between 1.30 and 1.28 across the bank.

 

I thought about inaccuracy, but it would still display a low SG compared to my starter battery.

You are most likely not charging the Trojans quite as much as you think and now have some sulphation.

You need to have some means of doing an equalisation charge (15.5volts), this will sort them out (I was going to say this'll fix it but that phrase is non PC these days!).

Don't worry so much about the 100% charge every other day, Trojans can take some abuse, a full charge once a week, or even less, will be fine as long as you can equalise once every month or two.

If you have sulphation the capacity (and SG) just settles at a lower level so the battery shows the outward signs (tail current) of full charge but its not.

SG should be similar to your starter battery, and the "green" SG of your starter confirms that your hydrometer is OKish

Don't worry, after only a month you can easily sort this out.

 

I suspect Trojans actually enjoy a really good discharge once in a while,.... take them down to 30!

 

.............Dave

 

But I am charging them to Trojan specs. And they are only in their fourth week! There can't be any sulphating yet, surely?

Edited January 31, 2015 by Loafer

[Tony Brooks]

Would they be warm from charging? If so the Sp. Gr. would be lower because the electrolyte has expanded. You should use a correction table to gte the true Sp. Gr. but you also need the temperature of the electrolyte.

[nicknorman]

I don't quite understand why, since you would think it was a fairly proportional relationship between SG and SoC, but the last bit of charge seems to make a disproportionally large difference in SG. Although 1% of AH tail current is pretty well full charged, it isn't quite and that little bit extra seems to make a fair difference. As Dave says, probably a touch of sulphation and you need to charge at 14.8v adjusted for temperature (so over 15v with cold batteries) and the occasional equalisation to 15.5, although in coming up to a year now, I have only EQd ours twice and they still have full capacity.

 

I would recommend a refractometer type of hydrometer, around £30 from eBay IIRC and can be read very accurately.

Edited January 31, 2015 by nicknorman

[Keeping Up]

I had the same readings from a new set of Varta batteries and Varta told me that they were within spec.

[Loafer]

Would they be warm from charging? If so the Sp. Gr. would be lower because the electrolyte has expanded. You should use a correction table to gte the true Sp. Gr. but you also need the temperature of the electrolyte.

No mate. It's a fairly cold battery bay and there was no sign of warmth while I was dipping the cells.

I don't quite understand why, since you would think it was a fairly proportional relationship between SG and SoC, but the last bit of charge seems to make a disproportionally large difference in SG. Although 1% of AH tail current is pretty well full charged, it isn't quite and that little bit extra seems to make a fair difference. As Dave says, probably a touch of sulphation and you need to charge at 14.8v adjusted for temperature (so over 15v with cold batteries) and the occasional equalisation to 15.5, although in coming up to a year now, I have only EQd ours twice and they still have full capacity.

 

I would recommend a refractometer type of hydrometer, around £30 from eBay IIRC and can be read very accurately.

 

I might well get one of those. Didn't know about them. Thanks!

[dmr]

 

I thought about inaccuracy, but it would still display a low SG compared to my starter battery.

 

But I am charging them to Trojan specs. And they are only in their fourth week! There can't be any sulphating yet, surely?

 

Well, they have travelled all the way from America and maybe sat in a warehouse here for a while too.

I purchased a new set of Numax a few years ago that were in a shocking state!

There should be a date stamp on the Trojans somewhere. The www will tell you how to decode it.

Its a good idea to give new batteries a good charge/equalise but this rarely gets a mention these days.

dunno where you are but I bet you a pint an equalise will sort this out.

 

...........Dave..

[dmr]

I don't quite understand why, since you would think it was a fairly proportional relationship between SG and SoC, but the last bit of charge seems to make a disproportionally large difference in SG. Although 1% of AH tail current is pretty well full charged, it isn't quite and that little bit extra seems to make a fair difference. As Dave says, probably a touch of sulphation and you need to charge at 14.8v adjusted for temperature (so over 15v with cold batteries) and the occasional equalisation to 15.5, although in coming up to a year now, I have only EQd ours twice and they still have full capacity.

 

I would recommend a refractometer type of hydrometer, around £30 from eBay IIRC and can be read very accurately.

 

 

http://evbatterymonitoring.com/webhelp/section_3.htm

 

see figure 18, not sure I believe it but its interesting.

 

..................Dave

[Loafer]

http://evbatterymonitoring.com/webhelp/section_3.htm

 

see figure 18, not sure I believe it but its interesting.

 

..................Dave

Yes it is. Thanks for that!

[Loafer]

You are most likely not charging the Trojans quite as much as you think and now have some sulphation.

You need to have some means of doing an equalisation charge (15.5volts), this will sort them out (I was going to say this'll fix it but that phrase is non PC these days!).

Don't worry so much about the 100% charge every other day, Trojans can take some abuse, a full charge once a week, or even less, will be fine as long as you can equalise once every month or two.

If you have sulphation the capacity (and SG) just settles at a lower level so the battery shows the outward signs (tail current) of full charge but its not.

SG should be similar to your starter battery, and the "green" SG of your starter confirms that your hydrometer is OKish

Don't worry, after only a month you can easily sort this out.

 

I suspect Trojans actually enjoy a really good discharge once in a while,.... take them down to 30!

 

.............Dave

30%? Wow. What sort of loaded voltage were you seeing when you decided to put them on charge?

[nicknorman]

http://evbatterymonitoring.com/webhelp/section_3.htm

 

see figure 18, not sure I believe it but its interesting.

 

..................Dave

Very interesting even. However it presumes a time relationship, whereas what I have observed is that the SG remains surprisingly low until absolutely fully charged, even when left for days in the nearly but not quite fully charged state. However I have no scientific-grade proof for that, it's just how it seems to me.

30%? Wow. What sort of loaded voltage were you seeing when you decided to put them on charge?

When we first got our T105s they were disappointing lazy. However after cycling them down to 30% SoC a couple of times, they gained a new vigour and displayed their rated capacity, so I am inclined to agree with Dave. If you look at the cycle life published by Trojan, there is very little difference in the total AH extractable in the life of the battery when cycling down to 30% vs 50%.

[Loafer]

Very interesting even. However it presumes a time relationship, whereas what I have observed is that the SG remains surprisingly low until absolutely fully charged, even when left for days in the nearly but not quite fully charged state. However I have no scientific-grade proof for that, it's just how it seems to me.

I'm also sure that my Trojans would man up and show a green, if they had stayed fully charged for 5 years like my engine start battery.

 

But these are NEW. I would have thought no sulphating yet.

[nicknorman]

I'm also sure that my Trojans would man up and show a green, if they had stayed fully charged for 5 years like my engine start battery.But these are NEW. I would have thought no sulphating yet.

Well as I said in my second bit, ours were disappointing at first until I gave them a good thrashing. At that stage I didn't have a hydrometer so I don't know if they were displaying low SG or not.

 

They are new to you, but what happened during their early childhood?

[dmr]

30%? Wow. What sort of loaded voltage were you seeing when you decided to put them on charge?

 

I really don't worry too much about voltage during discharge, I have a Smartgage and although I accept its not perfect I believe what its telling me.

Only real issue with deep discharges is that the inverter gets a bit stroppy, but we rarely use the inverter.anyway.

 

Trojans are spec'ed to go down to 20%. The 50% rule is a good guide but gets taken much too seriously, especially on this forum!

 

...........Dave

and some people (including Trojan???) say that continued very light discharge can be a BAD thing, I suspect 75% is ok but maybe 90 to 95 is not?.

 

............Dave

[Loafer]

I really don't worry too much about voltage during discharge, I have a Smartgage and although I accept its not perfect I believe what its telling me.

Only real issue with deep discharges is that the inverter gets a bit stroppy, but we rarely use the inverter.anyway.

 

Trojans are spec'ed to go down to 20%. The 50% rule is a good guide but gets taken much too seriously, especially on this forum!

 

...........Dave

 

and some people (including Trojan???) say that continued very light discharge can be a BAD thing, I suspect 75% is ok but maybe 90 to 95 is not?.

 

 

 

............Dave

Thanks dmr, but I really am interested in discharging voltages, believing for example that it would be down to 10.5V as you drew out the last 1% of charge. According to all the inter blurb anyway.

 

PLEASE have a look and let me know. I asked this a while ago on a separate thread, and no-one came up with any numbers.

 

Just 2 numbers will do - loaded voltage and alleged SOC, when you decide to recharge. Maybe Ah used by that time, too. Oh, and total battery capacity c20.

 

Thanks, mate!

[rogeriko]

All flooded batteries need about 50 cycles before they reach their full capacity. Just charge them at 15.5v for 3 or 4 hours (equalise) after you have fully charged them and they will be fine.

 

From Trojan website.

 

 

Edited January 31, 2015 by rogeriko

[nicknorman]

Thanks dmr, but I really am interested in discharging voltages, believing for example that it would be down to 10.5V as you drew out the last 1% of charge. According to all the inter blurb anyway.PLEASE have a look and let me know. I asked this a while ago on a separate thread, and no-one came up with any numbers.Just 2 numbers will do - loaded voltage and alleged SOC, when you decide to recharge. Maybe Ah used by that time, too. Oh, and total battery capacity c20.Thanks, mate!

The issue with ultimate discharge voltage is the need to avoid discharging a cell to beyond 0% SoC such that the voltage across it becomes reversed. This is very damaging. In an ideal world of course this would only occur once the battery's voltage fell below zero, but in reality due to the individual cells having slightly different capacities and starting States of charge, (and considering a 12v battery) you might have 5 cells with remaining juice and one that is now totally flat. The remaining 5 cells are now capable of pushing current through the flat cell so as to reverse the voltage across it. Bad news.

 

To avoid this scenario, the ultimate limit of 10.5v is created. Provided you don't go below this voltage, it is unlikely that any cell will be reverse biased ( ie have reverse voltage across it).

 

On your point about a chart of terminal voltage versus load and state of charge, it is not really feasible to produce such a chart because a number of variable factors combine to effect the terminal voltage. The amount of effective plate area, the internal resistance of each cell, and the state of charge of each cell (not necessarily the same as the other cells), the temperature, degree of sulphation and probably some other things all effect the resultant voltage. The Smartgauge is pretty good at giving an overall state of charge on discharge, and avoiding going below perhaps 20 or 30% assures that no cells are being reverse biased, so this is a better guide than the instantaneous terminal voltage under load.

[dmr]

Thanks dmr, but I really am interested in discharging voltages, believing for example that it would be down to 10.5V as you drew out the last 1% of charge. According to all the inter blurb anyway.

 

PLEASE have a look and let me know. I asked this a while ago on a separate thread, and no-one came up with any numbers.

 

Just 2 numbers will do - loaded voltage and alleged SOC, when you decide to recharge. Maybe Ah used by that time, too. Oh, and total battery capacity c20.

 

Thanks, mate!

 

Just to elaborate on wot Nick has said, and without repeating the previous thread, this really is not the way to go.

 

The only easy way to assess state of charge from voltage is to turn everything off and wait at least several minutes. This is not compatible with living on a boat. (I did it once and forgot to turn the fridge back on, big domestic trouble) Trying to get charge from LOADED voltage involves knowing the current and the internal resistance of the battery.This resistance is made up of the proper resistance of the metal bits, plus a sort of "electro-chemical" resistance which is complicated and variable. For example, if you have just done an equalisation it might be lowish. If you have not equalised for a while it will probably be increased due to the suplhate coating. As nick says it will probably also change with state of charge. Life is just too short to map this out for every condition, but an ex forum member did just this (and more) and built all this knowledge into his Smartgage I was a sceptic for many years, but I promise you it works!

 

...............Dave

[Loafer]

Many thanks for your very informative stuff above, guys! All present and correct.

 

However, I already knew all that. I'm merely CURIOUS, to see what voltages I would be seeing, if I took my batteries down to a low SOC with a typical Loafer load on, say 4-8A depending on the fridge's duty cycle.

 

I KNOW I can't use that as a measure of SOC, and nor am I trying to do that!

 

I'm just INTERESTED!!!

 

PLEASE, can someone just give me a couple of numbers, instead of ignoring my pleas for them and trying to re-educate me instead!!

 

I'm just interested, honestly!

[nicknorman]

Many thanks for your very informative stuff above, guys! All present and correct.However, I already knew all that. I'm merely CURIOUS, to see what voltages I would be seeing, if I took my batteries down to a low SOC with a typical Loafer load on, say 4-8A depending on the fridge's duty cycle.I KNOW I can't use that as a measure of SOC, and nor am I trying to do that!I'm just INTERESTED!!!PLEASE, can someone just give me a couple of numbers, instead of ignoring my pleas for them and trying to re-educate me instead!!I'm just interested, honestly!

Well I can't. Not because I am being mean and nasty or ignoring you, but just because there is no "right answer". However if you want a pure guess, 4 - 8A out of a 450AH bank is not much, it might perhaps give you 0.2v below the no-load voltage with cold batteries. But of course you are in a good position to find out for yourself - next time the batteries are down near 50%, leave them with zero load on for a few 10s of minutes, measure the voltage and then turn the loads on, re-measure the voltage.

 

So, looking at Trojan's no load voltage vs SoC, I suggest you don't take them below 11.6v when under you modest load.

Edited February 1, 2015 by nicknorman

[Radiomariner]

Going back to my seafaring days I recall that lead acid batteries, regardless of Ah capacity when fully charged should have a SG above 1.600 after a correction for temperature, and that is normally where the green section on the hydrometer starts. The best indication of battery defect was to keep a battery logbook' recording cell by cell voltage and SG checks under the same conditions once per month. A change in pattern indicates quite clearly, not only a defective cell, but one that is starting to fail. (which can then be given special attention)

I do not think correction for temperature is very important in this country, but on seagoing vessels it really mattered because of severe climate change between checks

 

Edited to add} I must be honest. I no longer practice what I preach above, far too much hassle. after all mine is a leisure craft!

Edited February 1, 2015 by Radiomariner

[smileypete]

Many thanks for your very informative stuff above, guys! All present and correct.

 

However, I already knew all that. I'm merely CURIOUS, to see what voltages I would be seeing, if I took my batteries down to a low SOC with a typical Loafer load on, say 4-8A depending on the fridge's duty cycle.

 

I KNOW I can't use that as a measure of SOC, and nor am I trying to do that!

 

I'm just INTERESTED!!!

 

PLEASE, can someone just give me a couple of numbers, instead of ignoring my pleas for them and trying to re-educate me instead!!

 

I'm just interested, honestly!

 

Sometimes the best way to learn is by observation.

 

Just wait for a resting voltage around 12.2V, then switch the fridge on or off and see how the voltage drops and recovers.

 

ETA: Spending a little bit of time here and there reading The Battery FAQ, plus a bit of time spent on observation, will easily give you the best understanding possible, you don't neeeed forum 'gurus' to give all the answers!

 

cheers, Pete.

~smpt~

Edited February 1, 2015 by smileypete

[Loafer]

Oh alright, I do accept all you guys are saying! But you are all missing my innocent little request. I have read all the battery FAQ's since Leclanche first made his 'pile'. (I think it was him anyway)

 

Here is my innocent request, re-worded for the gurus!:

 

PLEASE, would the next person who has a battery monitor, tell me his in-use voltage (i.e. under normal load) at the time that he thinks he ought to recharge. And also give me his best guess at SOC, from whatever data, at the same time.

 

Guys, how difficult can that be? !!