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Glynn

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7 minutes ago, WotEver said:

Whether the lead oxide is deep within the plate or on the surface can only affect the speed of the conversion and hence the current. The voltage is dictated by the basic reaction which as we’ve previously agreed is binary - it either happens or it doesn’t. 

 

I would be a bit cautious about the 'deep within the plate' and speed. It is more likely that the plate is more 'sponge' like with acid in contact with a very large surface area. Thermodynamics and steric effects will dictate which sites go first with the reaction to sulphate with the 'path of least resistance' (ie activation energy - to use the proper term) happening on the sites which favour the reaction best. The reaction with the more hindered sites may be slower as the ability to provide the required activation energy is lower. Splitting hairs I guess!

Actually it's not binary. It either happens or it doesnt or it goes backwards. Three outcomes. As it is an equilibrium, the electrons will appear or not - depending if the activation energy is achieved or they will reverse and be used up if the voltage is high enough.

I agree - I'll go with magic. I will check out the references later when we get back from the pub. In Braunston to try the Old Plough. Still busy here but we did see Tim and Pru sail past both ways .....and not in a particularly straight line.

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5 hours ago, WotEver said:

Yes it should :)

Why it doesn’t is one of life’s many mysteries and my (quite extensive) Googling research suggests that it isn’t fully understood by anyone. Unless someone can find a paper that offers an explanation?

this is interesting

 http://ecee.colorado.edu/~ecen2060/materials/lecture_notes/lead_acid_battery_paper.pdfhttp://ecee.colorado.edu/~ecen2060/materials/lecture_notes/lead_acid_battery_paper.pdf

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2 hours ago, WotEver said:

I can’t recall where I first learned this, it might have been Gibbo, but if you Google “2.041 volts” you will see many references to it including “Art in Chemistry, Chemistry in Art” and many others. 

In fairness, this reaction is generally referred to as the ‘basic reaction’ which suggests (as we know from observation) that there are other, secondary reactions going on, hence the fact that the battery voltage varies. 

Whether the lead oxide is deep within the plate or on the surface can only affect the speed of the conversion and hence the current. The voltage is dictated by the basic reaction which as we’ve previously agreed is binary - it either happens or it doesn’t. 

Gibbo once told me of an occasion that he took a sample of electrolyte from a battery which was being hard charged from 50% SoC and gave that sample to a Dr Hewitt PHD (Chemistry) and Dr Hewitt found chemicals there which had no right to be there and he couldn’t offer an explanation for their existence. However he noted that those chemicals would be effective in removing hardened sulphate, which Water and H2SO4 cannot do. So nobody truly understands where these compounds come from but it’s a good thing that they do or a LA battery would never work - it would be totally sulphated after a handful of cycles. 

So, like I said earlier in this thread - it’s magic. 

Other than water, lead and sulphuric acid, plates are often doped with antimony, selenium or calcium to strengthen plates or increase the voltage at which the battery gases respectively. Could these be the chemicals Dr Hewitt found? 

The web extract below gives information on battery plate construction.

LEAD ACID BATTERY PLATES

There are, in general, two methods of producing the active materials of the cell and attaching them to lead plates. These are known after the names of their inventors. 

1) Plante plates of formed lead acid battery plates. 
2) Faure plates or pasted lead acid battery plates.

Plante Plate

Plante Process

In this process two sheets of lead are taken and immersed in dilute H2SO4. When an current is passed into this lead acid cell from an external supply, then due to electrolysis, hydrogen and oxygen are evolved. At anode, oxygen attacks lead converting it into PbO2whereas cathode is unaffected because hydrogen can form no compound with Pb.

 

If the cell is now discharged then peroxide-coated plate becomes cathode, so hydrogen forms on it and combines with the oxygen of PbO2 to form water thus,
1497270055.PNGAt the same time, oxygen goes to anode which is lead and reacts to form PbO2. Hence the anode becomes covered with a thin film of PbO2.
By continuous reversal of the current or by charging and discharging the thin film of PbO2will become thicker and thicker and the cell polarity will take increasingly longer time to reverse. Two lead plates after being subjected to hundreds of reversals will acquire a skin of lead peroxide thick enough to process sufficiently high capacity. This process of making positive plates is known as formation. The negative lead acid battery plates are made of same process.

Structure of Plante Plate

plante plateIt is seen that since active material on a Plante plate consists of a thin layer of PbO2formed on and from the surface of the lead plate, it must be desirable to have a large superficial area in order to get an appreciable volume of it. The superficial area of lead acid battery plate can be increased by grooving or laminating. The figure shows a Plante positive plate which consists of a pure lead grid with finely laminated surfaces. The construction of these plates consists of a large number of thin vertical lamination which are strengthened at intervals by horizontal binding ribs. This results in increase of superficial area by a large extend. The main feature of construction of lead acid battery is to accommodate a large volume of active materials i.e. PbO2 in active plate.

Positive plates are usually produced by Plante Process and the plates are known as Plante Plates. The negative lead acid battery plates can also be manufactured by this process but for negative plate this process is impracticable.

Faure Plate

In Faure process, the active material is mechanically applied instead of being electrolytically developed out of lead plate itself as in Plante process. The active material which is in the form of red lead (Pb3O4) or litharge (PbO) or the mixture of two in various proportions, is pressed into the interstices of a thin lead grid which also serves as conductor of current. After pasting the grids with active material the plates are dried, hardened and assembled in a weak solution of sulfuric acid of specific gravity 1.1 to 1.2 and are formed by passing an current between them. For forming negative plate these plate are connected as cathodes. The oxygen evolved at the anode converts the lead oxide (Pb3O4) into lead peroxide (PbO2) and hydrogen evolved at cathode reduces the lead monoxide (PbO) into sponge lead (Pb).faure plate

Formation of positive plates involves conversion of lead oxide into lead peroxide. A high lead oxide, such as Pb3O4 is used from economic considerations both in current and time, although in practice a mixture of Pb3O4 is employed. Faure process is much suitable for manufacturing of negative Faure plates rather than positive lead acid battery plates.

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47 minutes ago, blackrose said:

I have the BEP DC Meter. Amps in/out on the domestic bank and volts on all 3 banks. For SoC I use a Smartgauge which also gives me volts on the domestics so it's handy as a cross-reference. 

image.jpeg.b903a92116cc989a243cb3cfbb62f2e0.jpeg

I think that is how I now find the Smartgauge useful.... as a cross reference, rather than an absolute. On it's own, without at least an ammeter, it can be the cause of problems for the naive.

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50 minutes ago, Richard10002 said:

I think that is how I now find the Smartgauge useful.... as a cross reference, rather than an absolute. On it's own, without at least an ammeter, it can be the cause of problems for the naive.

Yup, sound advice :)

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3 minutes ago, Glynn said:

Thanks for all the replies, its a very busy thread this !.

Another question, what would you say the amps draw would be for an "average" main hair drier powered by the inverter ?.

At least one average battery per hour:)

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On 08/10/2017 at 20:41, Glynn said:

Thanks for all the replies, its a very busy thread this !.

Another question, what would you say the amps draw would be for an "average" main hair drier powered by the inverter ?.

 

What is the power rating of this supposedly "average" hair dryer?

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On 08/10/2017 at 20:58, Glynn said:

I believe they are around 1500 watts to 2000 watts

 

Assuming yours is 2,000W, and assuming your inverter is 100% efficient (which it can't be), the current draw on your domestic batts will be 167A. Also assuming they can maintain 12v at this current (pretty unlikely). 

Call it a round 200A.

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7 minutes ago, Glynn said:

I meant what would be the amps drawn be whilst the hair drier is running ?. 

We have two hair driers on the boat. Mine is a cheap one and I use it for drying out the bilge or floor after the various spillages and leaks that one gets on a boat. Gillie has a big expensive one that she uses for drying her hair (how boring). We have that lovely TravelPower so Gillie is only allowed to dry hair whilst we are cruising (or possible battery charging). I don't know how much electricity it uses but the engine slows down, the TravelPower belt does a little squeal and the engine exhaust note sounds wonderful.

I reckon you could easily be looking at 150 amps at 12 volts.

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

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So in that case, a NASA BM2 with a 200amp shunt wont cope ?

 

The only reason I want to know is because Erindoors may want to dry her hair ( 2  - 3 minutes max ) in a morning and I want to know if a battery monitor with a 200 amp shunt would handle it.

Apart fromthis short use of high power everything else on the boat is very low consumption stuff.

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4 minutes ago, Glynn said:

Probably just a couple of LED lights and the fridge if it decides to come on at the same time.

Then you’d be fine. The BM2 might max out but it’s not at any kind of level that would do any damage. 

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On 08/10/2017 at 21:27, Glynn said:

Really ?

 

Have a guess... ;)

 

Was just kidding really to make you think about it. 200A for three minutes = 10AH. 

Will prolly be just fine as long as you fully recharge immediately.

(Which I bet you won't!)

 

 

 

Edited by Mike the Boilerman
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As I understand it, the BM2 will handle more than 200Ah, it just won't record them.

When I want to use the hoover, or the coffee maker, I make sure the engine is running. This ensures that the volts stay up while the big Amps are flowing, so the batteries don't suffer.

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4 minutes ago, Richard10002 said:

As I understand it, the BM2 will handle more than 200Ah, it just won't record them.

When I want to use the hoover, or the coffee maker, I make sure the engine is running. This ensures that the volts stay up while the big Amps are flowing, so the batteries don't suffer.

Good practise. It won’t only help stop the voltage from drooping but will also minimise the current being drawn through the shunt. 

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