Battery SG readings.

[Dr Bob]

49 minutes ago, Mike the Boilerman said:

 

I hold that the SG varies with height in the battery. The feeble bubbles created even during desulphation are too tiny and lacking in energy to effectively disrupt the stratification in the acid IMO. I reckon even serious turkey baster squirting only penetrates an inch or two below the top of the plates. 

A device to properly mix up the electrolyte needs inventing. 

I'm sure Rusty could knock up something involving an ecofan (other fans are available).

[MtB]

STOP that!

(Ecofans are available)

[Dr Bob]

There's quite a bit on tinternet re ultrasonics in batteries to reduce sulphation but I can't see any references to it helping stir up the acid, which I would have thought would happen. Circulation of the acid may be the only way. Not easy. How about lithiums?

[WotEver]

8 hours ago, Mike the Boilerman said:

I hold that the SG varies with height in the battery. The feeble bubbles created even during desulphation are too tiny and lacking in energy to effectively disrupt the stratification in the acid IMO. I reckon even serious turkey baster squirting only penetrates an inch or two below the top of the plates. 

A device to properly mix up the electrolyte needs inventing. 

All of the documentation out there on’t web says that an equalisation charge will stir up the electrolyte and eliminate stratification. Remember that the bubbles are coming from the entire surface of the plate and travelling upwards through the acid.

Do you have any evidence that batteries remain stratified (if they ever were) following a nice vigorous equalisation?  Have you measured SG, given the battery a good shake and measured it again? Maybe squirted the acid forcefully between the plates with a baster and tried again? Is there any documentation anywhere to support your supposition?

What I’m getting at is whether your suggestion actually exists in reality or simply appears over a few pints. 

[Alan de Enfield]

8 hours ago, Dr Bob said:

 Circulation of the acid may be the only way. Not easy. How about lithiums?

They would have to be quite small to be able to get them into the fill-holes, would they have little propellers so they could drive around inside the FLA and stir it up - aka the 1966 film "Fantastic Voyage"

Edited March 8, 2018 by Alan de Enfield

[MtB]

1 hour ago, WotEver said:

All of the documentation out there on’t web says that an equalisation charge will stir up the electrolyte and eliminate stratification. Remember that the bubbles are coming from the entire surface of the plate and travelling upwards through the acid.

Do you have any evidence that batteries remain stratified (if they ever were) following a nice vigorous equalisation?  Have you measured SG, given the battery a good shake and measured it again? Maybe squirted the acid forcefully between the plates with a baster and tried again? Is there any documentation anywhere to support your supposition?

What I’m getting at is whether your suggestion actually exists in reality or simply appears over a few pints. 

 

I find that several results taken from the same cell in quick succession rarely accurately agree with each other, as I suspect returning the sample stirs up the electrolyte a bit. This is what I'm basing my otherwise unsupported hypothesis on. And yes I've squirted the acid down vigorously with a baster and the result usually changes. But it also changes if I don't. This is using both my refractometer and my twin disc float type device. I've yet to find a method of measuring that gives reliable, repeatable results with no variation and I am wondering why.  Is it my instruments, my technique, or does the sample actually vary slightly each time its taken?

I agree with you, it needs testing. Anyone new to a field tends to ask questions the experts in the field think they already know the answer to. I'm wondering if the many statements you mention that the bubbles get rid of stratification are actually true. Is there evidence to support this? How big do the bubbles need to be? The converse of your statement about vigorous equalising getting rid of stratification kind of accepts it exists, and suggests bubbles too small don't get rid of it. 

 

[nicknorman]

1 minute ago, Mike the Boilerman said:

 

I find that several results taken from the same cell in quick succession rarely accurately agree with each other, as I suspect returning the sample stirs up the electrolyte a bit. This is what I'm basing my otherwise unsupported hypothesis on. And yes I've squirted the acid down vigorously with a baster and the result usually changes. But it also changes if I don't. This is using both my refractometer and my twin disc float type device. I've yet to find a method of measuring that gives reliable, repeatable results with no variation and I am wondering why.  Is it my instruments, my technique, or does the sample actually vary slightly each time its taken?

I agree with you, it needs testing. Anyone new to a field tends to ask questions the experts in the field think they already know the answer to. I'm wondering if the many statements you mention that the bubbles get rid of stratification are actually true. Is there evidence to support this? How big do the bubbles need to be? The converse of your statement about vigorous equalising getting rid of stratification kind of accepts it exists, and suggests bubbles too small don't get rid of it. 

 

Slightly at a tangent I know, but I have an etching tank for making PCBs, similar in shape to a battery cell ie tall and thin. The etchant is heated by an electrical heater inside a glass tube, at one end of the tank. At the bottom of the tank is a rubber tube with some tiny holes, and this is connected to an aquarium type air pump. When the pump is running, tiny bubbles rise up from this pipe and agitate/ mix the etchant so that it is both at an even temperature and the etchant is moving slightly over the surface of the PCB to bring new etchant into contact with the copper.

Bearing in mind how tiny and few the bubbles are, it is amazing how the etchant temperature becomes even - fighting convection because the heater only extends about 1/2 way down. So I can well believe that the bubbles produced when equalising are quite adequate to mix the electrolyte to an even concentration.

A dissolved mixture is quite reluctant to separate by gravity. For example, try centrifuging some beer to see if you can end up with stronger alcohol at the top to make spirits. I think you will struggle.

[smileypete]

12 hours ago, dmr said:

A while ago I tried to make up a "calibration fluid" using Citric Acid and some accurate scales but it was not too good, I could only get onto the very lowest part of the hydrometer scale so could not diagnose "scale" errors.

ISTR I used saturated salt solution to check a hydrometer:

'The density of a saturated solution at 25°C is 1.202 g/ml.'

https://www.google.co.uk/search?q=saturated+salt+solution+density

[Dr Bob]

1 minute ago, smileypete said:

ISTR I used saturated salt solution to check a hydrometer:

'The density of a saturated solution at 25°C is 1.202 g/ml.'

https://www.google.co.uk/search?q=saturated+salt+solution+density

Clever.

[smileypete]

18 minutes ago, Dr Bob said:

Clever.

The other way was comparing the weight of a small volume of deionised water in a measuring cap to the same of battery acid on some cheap digital scales, and working out the electrolyte strength from there. I s'pose you could use salt solution instead of the water.

A large syringe would give a more exact volume and be less likely to spill, but a small measuring cap with good markings can be surprisingly repeatable

1 hour ago, Mike the Boilerman said:

I agree with you, it needs testing. Anyone new to a field tends to ask questions the experts in the field think they already know the answer to. I'm wondering if the many statements you mention that the bubbles get rid of stratification are actually true. Is there evidence to support this? How big do the bubbles need to be? The converse of your statement about vigorous equalising getting rid of stratification kind of accepts it exists, and suggests bubbles too small don't get rid of it.

Would have thought constant current at C/30 would generate some nice bubbles.

Edited March 8, 2018 by smileypete

[dmr]

26 minutes ago, smileypete said:

ISTR I used saturated salt solution to check a hydrometer:

'The density of a saturated solution at 25°C is 1.202 g/ml.'

https://www.google.co.uk/search?q=saturated+salt+solution+density

Wish I had thought of that, I think I spent a few pounds on getting boxes of citric acid at the chemists!!! I thought about doing a weight and volume thing but I think I decided that the kitchen scales did not have enough resolution. I have now got a little drug dealer electronic scales (for mixing small quantities of epoxy ) so might try again, but the saturated salt sounds best. I've now got a rotating dial hydrometer and am pretty sure its not correctly calibrated so would like to check it.

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

[rusty69]

5 minutes ago, dmr said:

I have now got a little drug dealer electronic scales

They should be great for acid.

[cuthound]

On 06/03/2018 at 08:40, Mike the Boilerman said:

 

Why the advice to wait until fully charged then? I'm fishing for the boundary. Or can a battery be desulphated in any state of charge?

Sorry for being late to the party. Life seems to be getting in the way of being on the forum lately.

Because charging at a higher than normal voltage shakes the active material from the plates and erodes them. That is why periodic equalising should only be done when necessary if you want the longest battery life

 

On 06/03/2018 at 09:14, Mike the Boilerman said:

 

Yes that is a big unknown. Cuthound holds the brand in high regard though. In addition I was too ignorant on the day I purchased them to think of measuring the SG and terminal voltage before buying them, so I may have been sold a pup. 

Although I have been retired for almost 5 years  I don't think much has changed with industrial/commercial batteries that I am very familiar with. Yuasa were considered to be  most cost effective batteries in terms of cost versus performance and longevity.

Rolls batteries (who have reverted to the Rolls brand for commercial use since Surrette dropped the Hawker Energy brand) were the best for performance and longevity because they used thicker plates of pure lead but cost much to buy than their competitors. It took BT (Europe's largest battery user) 25 years to realise that lead-alloy plates don't last as long. Eventually they persuaded Yuasa to produce pure lead thick plate batteries for them at a realistic price and finally got VRSLA's that would last 8-10 years without needing to be kept in a cooled environment. (Telephone exchange batteries are located in the equipment racks where summer temperatures can reach 40-45°C), unlike data centre batteries which are kept in an environmentally controlled to 20°C battery room.

 

On 06/03/2018 at 10:20, nicknorman said:

Yuasa certainly used to be a quality  brand. But I think those days are long over.

That may be the case for their leisure batteries but Yuasa batteries are used by the majority of comms companies and data centres.

 

On 07/03/2018 at 10:39, Mike the Boilerman said:

 

Hmmm so a proper desulphate can take days on end eh?

My experience is that desulphation is quicker if the equalising is stopped when the battery begins to gas vigorously and restarted after a short rest.

 

On 07/03/2018 at 22:19, Mike the Boilerman said:

A device to properly mix up the electrolyte needs inventing. 

I used to work with an ex-submariner who said that diesel-electric submarines used to pump compressed air through the batteries when charging to significantly reduce charge times and thus time on the surface,  where they were vulnerable to attack.

I'm sure Bizzard could knock something up from a schraeder valve a bit of rubber hose and an old bicycle pump.