Sealed or open wet cell battery's?

[Graham.m]

You're right of course, but to get more plate area within a given size of battery, you have to make the plates thinner. So I guess it's chicken and egg as to whether it's more plate area = thinner plates, or thinner plates = more plate area.

 

Not sure what you are saying seems to contradict itself.

[nicknorman]

Not sure what you are saying seems to contradict itself.

 

Not when I read it again. Do explain though, perhaps I'm missing something as it seems quite clear to me.

[Graham.m]

Not when I read it again. Do explain though, perhaps I'm missing something as it seems quite clear to me.

 

I am not sure how many plates you think a cell has one, two or many? Seem it can have an unlimited number

[nicknorman]

I am not sure how many plates you think a cell has one, two or many? Seem it can have an unlimited number

Err no, that is why I said plate area, not number of plates (of which as you mentioned earlier, a cell has 2). Can you show me why you think I think "it can have an unlimited number"? As I said earlier, you seem to be trying to pick an argument out of nothing and it is getting tiresome. God help your customers.

[Graham.m]

Err no, that is why I said plate area, not number of plates (of which as you mentioned earlier, a cell has 2). Can you show me why you think I think "it can have an unlimited number"? As I said earlier, you seem to be trying to pick an argument out of nothing and it is getting tiresome. God help your customers.

 

I think we agree to differ, your explanation does not paint the right picture in my mind. Could be I am tired at the end of a long day

[peterboat]

when choosing my generator i went for the wispergen it also runs central heating and charges at 72 amps at 12 volt it really is silent. for me it is the best way .75 of a litre at full chat going down to a third of a litre when idling, whilst these gennies are expensive they do two jobs rather than one

[Robbo]

 

Is that 200 Ah per day? It would indeed be interesting to see the result of a feasibility study.

Yep my bad, 200ah a day. They do smaller versions as well. If your power needs are covered by solar during summer then these look to be a nice add on for winter power.

 

It's very easy to do running costs as it provides power when needed so is a direct litre of fuel per provided kW. Although if you use more amps than the system provides (8.8amp on the 200ah version) when using high powered items you'll use the batteries, so adding a conversion factor from charging. Although this percentage will be high due to the low charging amps so will be near 100% efficiency. A genny has many more factors to consider.

Edited November 10, 2015 by Robbo

[Graham.m]

Yep my bad, 200ah a day. They do smaller versions as well. If your power needs are covered by solar during summer then these look to be a nice add on for winter power.

 

It's very easy to do running costs as it provides power when needed so is a direct litre of fuel per provided kW. Although if you use more amps than the system provides (8.8amp on the 200ah version) when using high powered items you'll use the batteries, so adding a conversion factor from charging. Although this percentage will be high due to the low charging amps so will be near 100% efficiency. A genny has many more factors to consider.

 

According to the tech data 10 litres of fuel provides 11.1KWH/925AH at a cost in the UK of £78.00

 

Ed:

A litre of diesel has about 11.1KWH at say £0.80

 

I wonder if NiFe batteries and fuel cells could be the long term way to go

Edited November 10, 2015 by Graham.m

[Robbo]

 

According to the tech data 10 litres of fuel provides 11.1KWH/925AH at a cost in the UK of £78.00

 

Ed:

A litre of diesel has about 11.1KWH at say £0.80

 

I wonder if NiFe batteries and fuel cells could be the long term way to go

You get 2 pack of 2 for £78, so around £3.55 a kW.

 

Diesel generators arnt efficient especially at charging batteries and their isn't a direct link between fuel and end kW used.

Edited November 10, 2015 by Robbo

[Graham.m]

You get 2 pack of 2 for £78, so around £3.55 a kW.

 

Diesel generators arnt efficient especially at charging batteries and their isn't a direct link between fuel and end kW used.

:-) Miss the 2 pack bit

 

Methanol should be obtainable at nearer the diesel price per litre. Depends on what else is in the fuel cartridge

 

Only one problem I see is BSS. Methanol vapour is heavier than air therefore could hang in bilges.

 

If methanol as supplied for the Bio diesel market is OK then it is highly possible that there efficiencies could lean the fuel cells way.

Edited November 10, 2015 by Graham.m

[Top cat]

What I am taking from this argument is :

 

You need to consider not only ones total power daily requirements but also the peak loads when designing your electrical system.

It's best to avoid the occasional high but short duration load, so for example I would be better boiling the kettle by gas rather than use an electric kettle on the inverter. But if I must use an electric kettle then a 1Kw one is kinder to my batteries than a 2.5Kw one.

There doesn't seem much point in fitting an inverter much bigger than 1500W as thats a bit above the max load that my 400Ah liesure battery should be asked to provide.

Any battery regardless of cost and quality will die prematurely if not properly looked after .

 

Top Cat

[nicknorman]

What I am taking from this argument is :

You need to consider not only ones total power daily requirements but also the peak loads when designing your electrical system.

It's best to avoid the occasional high but short duration load, so for example I would be better boiling the kettle by gas rather than use an electric kettle on the inverter. But if I must use an electric kettle then a 1Kw one is kinder to my batteries than a 2.5Kw one.

There doesn't seem much point in fitting an inverter much bigger than 1500W as thats a bit above the max load that my 400Ah liesure battery should be asked to provide.

Any battery regardless of cost and quality will die prematurely if not properly looked after .

Top Cat

Yes, however it is all a compromise. We have 450AH of batteries and routinely use a 2kw electric kettle, which takes about 200A out of the batteries, but of course for less than 5 minutes. Perhaps this has a marginal life-shortening effect (although they are still at 100% capacity after 2 years) but is the extra cost and inconvenience of having extra battery capacity to make the peak current per AH capacity less, worth it? In our case I'd say no. The batteries cope with the C2 load albeit giving a bit less terminal voltage than our previous leisure batteries did. But it would be another £200 to add more capacity, and it would not be easy to find space for them, so I think the overall compromise we have is right. I doubt the £200 could be justified in terms of any battery life extension.

[Graham.m]

Basdically I agree with you adding

 

To get the best life and economy out of the batteries, the aim should be not to use more than 15 or 20% of your bank in 24 hours. 400A/H would give a max of say 80A/H

 

That batteries fare better when they are discharged at about a 20th of their capacity. A big discharge say a 1KW kettle via an inverter, say a 100A for ten minutes will take not 16.6A/h out of the battery but nearer 32A/h.

 

As part of the design it is important to design into the system how the discharge is going to be put back into the battery in the worst situation, a dark 21st December. There are few choice Fuel cells, generators etc, note that solar cell are not there. In the summer, June, they can have a part to play, but if the money goes on PV there will be no recharge resource on 21st December.

 

Also it is important not just to consider the DC needs but the AC needs as well. Considering the most efficient and economical way of supplying this AC need without hammering batteries.

[nicknorman]

That batteries fare better when they are discharged at about a 20th of their capacity. A big discharge say a 1KW kettle via an inverter, say a 100A for ten minutes will take not 16.6A/h out of the battery but nearer 32A/h.

 

This isn't true. It will be 16.6AH. I think you are confused as to where the Peukert concept applies, and where it doesn't.

[Graham.m]

Yes, however it is all a compromise. We have 450AH of batteries and routinely use a 2kw electric kettle, which takes about 200A out of the batteries, but of course for less than 5 minutes. Perhaps this has a marginal life-shortening effect (although they are still at 100% capacity after 2 years) but is the extra cost and inconvenience of having extra battery capacity to make the peak current per AH capacity less, worth it? In our case I'd say no. The batteries cope with the C2 load albeit giving a bit less terminal voltage than our previous leisure batteries did. But it would be another £200 to add more capacity, and it would not be easy to find space for them, so I think the overall compromise we have is right. I doubt the £200 could be justified in terms of any battery life extension.

 

Yes I appreciate your view. But perhaps that 2Kw via an inverter for 5 mins, say 30A/H, stressing the plates and pulling the lead off and the heat inducted in that battery is doing more damage than you believe. I would strongly suspect that using the batteries to boil that kettle as a regular thing once or twice a day, could easily take 20%+ off the battery life. You say your batteries still have 100% of their new capacity after two years. How do you know that and what capacity test have you done?

[Graham.m]

This isn't true. It will be 16.6AH. I think you are confused as to where the Peukert concept applies, and where it doesn't.

 

Cannot agree. Drawing heavy loads off batteries that are not designed for it causes the capacity to drop through the internal energy used just to get the charge out of the plates. Normally the delivered charge comes from the surface of the plates and is released easily and gradually replaced by the charge deep in the plates. When a heavy discharge is made the plate's surface cannot supply it and it has to be pulled from within the plate, which uses more energy and thus increases the discharge rate of the battery.

[nicknorman]

Yes I appreciate your view. But perhaps that 2Kw via an inverter for 5 mins, say 30A/H, stressing the plates and pulling the lead off and the heat inducted in that battery is doing more damage than you believe. I would strongly suspect that using the batteries to boil that kettle as a regular thing once or twice a day, could easily take 20%+ off the battery life. You say your batteries still have 100% of their new capacity after two years. How do you know that and what capacity test have you done?

 

Whilst a little heat is obviously produced, it has no visible effect on the temperature sensor's reading (although of course that is measuring electrolyte temperature, not plate temperature), ie less than 1 degree increase in electrolyte temperature.

 

It may be that battery life is reduced (probably is) although we are both guessing at how much. If I were to add another pair of T105s it would cost an additional 50% (ie going from 2 pairs to three). Even disregarding the physical issues, I don't think we can say that the additional cost would do anything other than break even on a corresponding life increase.

 

Of course, we don't have to use the electric kettle. We don't have to use the lights or tv either. In fact we could have the battery master switch permanently turned off, and then the batteries would last for ages! My point is that there is another compromise to be had between convenience and cost. Choosing the cheapest way is a common British trait, but rarely a good one.

 

As to battery capacity, I have an Smartgauge and an AH-counting gauge (Mastershunt). As you probably know, the former gives a SoC reading based on the actual capacity at the time, the latter gives an SoC based on the AH capacity set by the user. Thus if the reading are essentially the same, this shows that the actual capacity is the same as the set capacity. In the case of the open wet leisure batteries we used to have, I found them losing capacity fairly quickly - down to 50% after 6 months or so - although it could be restored by equalisation for a while. By 2 years they were failing to take charge well and I couldn't get the capacity back up by equalisation. In other words, I am familiar with observing a set of batteries gradually losing capacity - the Smartgauge reading would fall off much faster than the Mastershunt.

 

In the case of our current batteries the Smartgauge reading is if anything slightly ahead of the Mastershunt on discharge, showing that the capacity is at least that stated, coming up to 2 years old.

Edited November 10, 2015 by nicknorman

[nicknorman]

Cannot agree. Drawing heavy loads off batteries that are not designed for it causes the capacity to drop through the internal energy used just to get the charge out of the plates. Normally the delivered charge comes from the surface of the plates and is released easily and gradually replaced by the charge deep in the plates. When a heavy discharge is made the plate's surface cannot supply it and it has to be pulled from within the plate, which uses more energy and thus increases the discharge rate of the battery.

We've had this argument before (on the forum I mean) and I prevailed. Within the battery there are some chemicals and when they react together, an electron migrates between the plates for each molecule of the chemicals. Thus the chemical energy in terms of mass of reagents directly relates to the number of electrons that move between the plates. Electrons can't magically disappear.

 

What you refer to is the power efficiency. So with a high discharge, the internal resistance dissipates power (including the effects you describe) which manifests itself as voltage drop. But you can't have "current drop" so the current efficiency, in terms of the number of AH taken out per amount of chemical reaction, remains constant. So if you want to tell me that taking a high discharge wastes energy, I'll agree. But if, as you did, you want to tell me that it wastes AH for a given current, this is wrong.

 

Peukert is relevant for "time to run" type calculations because a battery is deemed flat when it's terminal voltage reaches a certain value, say 10.5v. At a higher current, this terminal voltage will be reached after less AH has been taken out, thus the capacity of the battery is less at higher currents, but only because of the definitions used.

 

You will find a paper in the Internet about this, written by someone much cleverer than me. Good AH counters use Peukert only to effect the "time to run" display (which is pretty useless for a boat, with significantly time-varying loads) but not for SoC calculations. I changed the Peukert exponent on my Mastershunt to 1 as an experiment, I could detect no change in behaviour of the SoC indication.

Edited November 10, 2015 by nicknorman

[Graham.m]

Whilst a little heat is obviously produced, it has no visible effect on the temperature sensor's reading (although of course that is measuring electrolyte temperature, not plate temperature), ie less than 1 degree increase in electrolyte temperature.

 

It may be that battery life is reduced (probably is) although we are both guessing at how much. If I were to add another pair of T105s it would cost an additional 50% (ie going from 2 pairs to three). Even disregarding the physical issues, I don't think we can say that the additional cost would do anything other than break even on a corresponding life increase.

 

Of course, we don't have to use the electric kettle. We don't have to use the lights or to either. In fact we could have the battery master switch permanently turned off, and then the batteries would last for ages! My point is that there is another compromise to be had between convenience and cost. Choosing the cheapest way is a common British trait, but rarely a good one.

 

As to battery capacity, I have an Smartgauge and an AH-counting gauge (Mastershunt). As you probably know, the former gives a SoC reading based on the actual capacity at the time, the latter gives an SoC based on the AH capacity set by the user. Thus if the reading are essentially the same, this shows that the actual capacity is the same as the set capacity. In the case of the open wet leisure batteries we used to have, I found them losing capacity fairly quickly - down to 50% after 6 months or so - although it could be restored by equalisation for a while. By 2 years they were failing to take charge well and I couldn't get the capacity back up by equalisation. In other words, I am familiar with observing a set of batteries gradually losing capacity - the Smartgauge reading would fall off much faster than the Mastershunt.

 

In the case of our current batteries the Smartgauge reading is if anything slightly ahead of the Mastershunt on discharge, showing that the capacity is at least that stated, coming up to 2 years old.

 

So what temperature do the plates have to be to raise the temperature of the electrolyte 1 degree (C. I assume)

 

Why is the capacity of a battery reduced when it is subject to a heavier discharge rate?

 

J185P Trojan Battery Deep Cycle

Trojan 12 volt deep cycle battery

AH @ 20HR -195

AH @ 5HR - 160

Capacity in minutes

@25 amps - 375

@75 amps - 95

I am sorry but the Smartgauge does not measure capacity, it measures the battery voltage and applies an an algorithm based on voltage v state of charge, which has its problems. Using a shunt only tells what current has been used by the system and uses data put in by the user to get to a stage of charge. Neither actually measures the charge in the battery. The only way I know to measure state of charge with any accuracy is to use a hydrometer and measure the SG. Even that does not give a capacity.

[ditchcrawler]

:-) Miss the 2 pack bit

 

Methanol should be obtainable at nearer the diesel price per litre. Depends on what else is in the fuel cartridge

 

Only one problem I see is BSS. Methanol vapour is heavier than air therefore could hang in bilges.

 

If methanol as supplied for the Bio diesel market is OK then it is highly possible that there efficiencies could lean the fuel cells way.

They run speed boats around here on Methanol. We use to use it Offshore and its horrible , if it catches fire like hydrogen you cant see the flame. Not sure the BSS has said anything about it yet but some sea going boats seem to be fitting them.

[nicknorman]

So what temperature do the plates have to be to raise the temperature of the electrolyte 1 degree (C. I assume)

 

Why is the capacity of a battery reduced when it is subject to a heavier discharge rate?

 

J185P Trojan Battery Deep Cycle

Trojan 12 volt deep cycle battery

 

AH @ 20HR -195

AH @ 5HR - 160

 

Capacity in minutes

@25 amps - 375

@75 amps - 95

 

I am sorry but the Smartgauge does not measure capacity, it measures the battery voltage and applies an an algorithm based on voltage v state of charge, which has its problems. Using a shunt only tells what current has been used by the system and uses data put in by the user to get to a stage of charge. Neither actually measures the charge in the battery. The only way I know to measure state of charge with any accuracy is to use a hydrometer and measure the SG. Even that does not give a capacity.

I've already explained why the stated capacity is lower at higher discharge currents. Please read my post as I really don't want to repeat it.

The Smartgauge is not perfect but it is remarkably good during discharge. I consistently get SoC readings within a few % of the Mastershunt as I have done since these batteries were new. By contrast, as I said I have observed the wildly differing readings between the two devices when the old batteries were losing capacity (eg SG on 50% with MS on 75%). So I agree it is not a categoric indications that my batteries are at their original capacity but the absence of any change in the relationship between the 2 sets of readings is good enough for me, and as good as it can be without doing a damaging full discharge cycle.

[ditchcrawler]

 

So what temperature do the plates have to be to raise the temperature of the electrolyte 1 degree (C. I assume)

 

Why is the capacity of a battery reduced when it is subject to a heavier discharge rate?

 

J185P Trojan Battery Deep Cycle

Trojan 12 volt deep cycle battery

AH @ 20HR -195

AH @ 5HR - 160

Capacity in minutes

@25 amps - 375

@75 amps - 95

I am sorry but the Smartgauge does not measure capacity, it measures the battery voltage and applies an an algorithm based on voltage v state of charge, which has its problems. Using a shunt only tells what current has been used by the system and uses data put in by the user to get to a stage of charge. Neither actually measures the charge in the battery. The only way I know to measure state of charge with any accuracy is to use a hydrometer and measure the SG. Even that does not give a capacity.

All good stuff but if you observe your batteries over a period of time with both ah used and voltages at rest you get a pretty good idea of your battery capacity and how its tailing off with use. I dont say you can state that your 110 ah batteries are now 97.5 ah but you can tell when they are somewhere near half knackered. And yes I have sat there taking readings from batteries every 15 minutes, adjusting the load and recording the temperatures. On my boat I just look at the volts and Ah used each morning before starting the engine and thats good enough for me. My batteries are 4 years old and still probable 75%+ of original capacity. I must admit to two things. When I fitted Torjans I didn't take into account of the voltage depression on load and even today wouldnt know where to find that info and the other point is that I have run them a bit low on water. So over all I am very pleased with them and would fit them again.

[nb Innisfree]

Batteries can last for years and years if you are prepared to live in the stone age.

 

Batteries are dying from the moment you start using them so get used to it and move on to the next batch.

 

The batteries are dead - long live the batteries!

[Top cat]

We have replaced our 2.5Kw kettles with 1 Kw ones mainly because when used at home they are less likely to draw more than our solar panels are producing and being smaller are just right for 2 mugs.

I moved to the lower wattage kettle on the boat in the belief that on the odd occasion that we run the kettle on the inverter that we are being kinder to the batteries. This is because although the Ah used to boil is slightly higher (takes longer so more time for heat to be lost, smaller vessel so surface area to volume greater = more heat lost) with the smaller kettle the current is much lower.

Likewise I have limited the hair dryer to 1Kw by blocking the max power position on the switch.

So rather than adding more batteries to cope with high loads we have limited the max load to about C/4

So when I replaced the inverter recently I didn't spend the extra for a 3Kw one.

 

The 20% discharge recommendation is interesting as thats pretty much what we end up at if we take a day off and get no sun.

 

Our 2 1/2yr old cheap liesure batteries are easily doing all we require, I'm not sure what the capacity has dropped to but I suspect not by much.

Top Cat

[Graham.m]

We've had this argument before (on the forum I mean) and I prevailed. Within the battery there are some chemicals and when they react together, an electron migrates between the plates for each molecule of the chemicals. Thus the chemical energy in terms of mass of reagents directly relates to the number of electrons that move between the plates. Electrons can't magically disappear.

 

What you refer to is the power efficiency. So with a high discharge, the internal resistance dissipates power (including the effects you describe) which manifests itself as voltage drop. But you can't have "current drop" so the current efficiency, in terms of the number of AH taken out per amount of chemical reaction, remains constant. So if you want to tell me that taking a high discharge wastes energy, I'll agree. But if, as you did, you want to tell me that it wastes AH for a given current, this is wrong.

 

Peukert is relevant for "time to run" type calculations because a battery is deemed flat when it's terminal voltage reaches a certain value, say 10.5v. At a higher current, this terminal voltage will be reached after less AH has been taken out, thus the capacity of the battery is less at higher currents, but only because of the definitions used.

 

You will find a paper in the Internet about this, written by someone much cleverer than me. Good AH counters use Peukert only to effect the "time to run" display (which is pretty useless for a boat, with significantly time-varying loads) but not for SoC calculations. I changed the Peukert exponent on my Mastershunt to 1 as an experiment, I could detect no change in behaviour of the SoC indication.

 

We've had this argument before (on the forum I mean) and I prevailed. Within the battery there are some chemicals and when they react together, an electron migrates between the plates for each molecule of the chemicals. Thus the chemical energy in terms of mass of reagents directly relates to the number of electrons that move between the plates. Electrons can't magically disappear.

 

What you refer to is the power efficiency. So with a high discharge, the internal resistance dissipates power (including the effects you describe) which manifests itself as voltage drop. But you can't have "current drop" so the current efficiency, in terms of the number of AH taken out per amount of chemical reaction, remains constant. So if you want to tell me that taking a high discharge wastes energy, I'll agree. But if, as you did, you want to tell me that it wastes AH for a given current, this is wrong.

 

Peukert is relevant for "time to run" type calculations because a battery is deemed flat when it's terminal voltage reaches a certain value, say 10.5v. At a higher current, this terminal voltage will be reached after less AH has been taken out, thus the capacity of the battery is less at higher currents, but only because of the definitions used.

 

You will find a paper in the Internet about this, written by someone much cleverer than me. Good AH counters use Peukert only to effect the "time to run" display (which is pretty useless for a boat, with significantly time-varying loads) but not for SoC calculations. I changed the Peukert exponent on my Mastershunt to 1 as an experiment, I could detect no change in behaviour of the SoC indication.

 

I am not arguing with you, I only state have I have learnt over 50 years of using and studying the technology if it does not suit you that is up to you. I gather you consider yourself an expert.

 

To product heat and remove lead from the plates something in the battery is doing work, the energy to do that work is produced by the battery. Additionally the work being done to boil the kettle uses energy from the battery. The two combined remove energy from the battery. Thus I contend reduce the amount of energy the battery has stored, therefore the capacity has been reduce and some wasted by using a discharge rate higher than the design rate.

 

As I do not have detailed knowledge of the algorithms used in the in your Mastershunt I will not comment.