Lifepo4 battery too cheap?

[MrFish]

Hot water is not really so much of an issue as i will be installing one of the new Eberspacher S3 D4 units. This is in addition to engine heating and calorifier heating element.  I estimate that the solar will let me short for about 3 to 4 months of the year, which is when i would have to rely on the Travel Power and maybe rely more on gas. I realy dont mind gas hobs so much but i have yet to find a gas oven that performs as well as i would like.

[Tony1]

32 minutes ago, IanD said:

 

All true -- but bear in mind that if the OP uses electricity for cooking (and kettle, and toaster, and microwave, and PC, and...) his usage is likely to be significantly greater than yours.

 

A power audit is absolutely essential to make all these decisions, becasue different people have different power requirements so it's difficult to say "it works for me, so it will work for you"... 🙂

 

Propane contains 50MJ/kg, diesel energy is 37MJ/l. Using the diesel to power a generator and then an induction hob via an inverter is about 20% efficient, meaning 7.5MJ of energy ends up in the pan from each litre of diesel; if diesel cost is £1.20/l  this means the cost is 16p/MJ. Burning propane on a ring about 40% of the energy ends up in the pan, so 20MJ from 1kg of gas. If a 13kg Calor bottle costs £36, this is £2.77/kg, meaning 14p/MJ -- pretty much the same as a diesel generator.

 

However if you charge your batteries by running the diesel propulsion engine the cost will be something like 2.5x higher than using a generator because the efficiency (engine+alternator) is much lower, this puts the cooking cost up to 40p/MJ which is *much* higher than gas. But if you have spare solar power instead of burning diesel, this will bring the cost down again somewhat.

 

Which means that if you have solar and a generator (like an electric boat...) cooking with electric is cheaper than gas, if you have solar and a diesel engine for charging (like you) it's more expensive, with just a diesel and no solar it's a *lot* more expensive.

 

Which reminds me, I need to get on the case and buy a small toaster as well as an electric hob.

In the summer I am finding that even after recharging and heating up the water, I still switch off the MPPTs in early or mid afternoon, so there is a lot more free energy I could be using. 

Its not quite free, of course, because cycling more energy through the batteries will mean proportionally shortening their lifespan, but I'm hoping batteries will become significantly cheaper over the next decade anyway, and in any case I may be in a different boat and cruising on the French canals by then, since it appears I may well be eligible for Dutch citizenship  😁

 

 

 

 

Edited March 4, 2023 by Tony1

[MtB]

55 minutes ago, MrFish said:

Hot water is not really so much of an issue as i will be installing one of the new Eberspacher S3 D4 units. This is in addition to engine heating and calorifier heating element.  I estimate that the solar will let me short for about 3 to 4 months of the year, which is when i would have to rely on the Travel Power and maybe rely more on gas. I realy dont mind gas hobs so much but i have yet to find a gas oven that performs as well as i would like.

 

This fits in well as its the hob that really sucks the power. The layman tends to imagine it is the other way around, i.e. the hob sips the power and the oven being bigger, gobbles it up. But no, a hob might typically be 8kW or 10kW for all four rings but built-in fan ovens for houses that perform superbly well might only draw 3kW, and sometimes a lot less.

 

Curiously it is getting really difficult to find out from on-line retailers what ovens for sale actually draw in terms of current. They all seem to quote a "duty cycle" instead, this being quoted in kWh per cycle. Utterly meaningless when working out what power supply they need! 

[MrFish]

Yeah the hobs will just keep pumping out power because it has no idea what temperature the food needs to reach. Whereas the oven is a contained insulated box that will turn off the heating elements when it reaches the set temperature. I think this is why the oven manufacturers look at kwh averages but they are still obliged to tell you the max current draw.  Its looking at all those potential peak loads that i am being careful to calculate.

 

The biggest down side of the lithiums that i can see is the max current draw. If you are lucky enough to have shore power then the mulitplus will balance where it draws power from, but if you cant do that then the batteries need to have a higher max discharge current or have a balanced parallel system. 

[magnetman]

12 minutes ago, MrFish said:

Yeah the hobs will just keep pumping out power because it has no idea what temperature the food needs to reach. Whereas the oven is a contained insulated box that will turn off the heating elements when it reaches the set temperature. I think this is why the oven manufacturers look at kwh averages but they are still obliged to tell you the max current draw.  Its looking at all those potential peak loads that i am being careful to calculate.

 

The biggest down side of the lithiums that i can see is the max current draw. If you are lucky enough to have shore power then the mulitplus will balance where it draws power from, but if you cant do that then the batteries need to have a higher max discharge current or have a balanced parallel system. 

Lithium Titanate batteries have very high C rates. 

 

Worth considering. 10C is doable. 

 

Bimble were claiming they were going to carry them but not sure of they have them or not. 

 

I'd prefer to see a smaller bank of higher discharge batteries rather than a larger bank of lower discharge batteries. 

 

A few people have built batteries using the cylindrical YinLong cells but these are often re-wrapped used cells from chinese electric buses. 

 

Amazing capability these things have and they are very safe. 

Bimble 

 

https://www.bimblesolar.com/batteries/lto-longlife-lithium-batteries

 

Not cheap! 

 

 

A 2Kwh 48v module can discharge 150a which is 7200w. 

 

I think they are doing the BMS as an external unit which is sensible as the batteries themselves are liable to last longer than the electronics. 

 

some suggestions of 20,000 cycles for these which is quite useful for something like cooking. 

[MtB]

21 minutes ago, MrFish said:

Yeah the hobs will just keep pumping out power because it has no idea what temperature the food needs to reach. Whereas the oven is a contained insulated box that will turn off the heating elements when it reaches the set temperature. I think this is why the oven manufacturers look at kwh averages but they are still obliged to tell you the max current draw.  Its looking at all those potential peak loads that i am being careful to calculate.

 

The biggest down side of the lithiums that i can see is the max current draw. If you are lucky enough to have shore power then the mulitplus will balance where it draws power from, but if you cant do that then the batteries need to have a higher max discharge current or have a balanced parallel system. 

 

Being pedantic but practical, the lithium cells themselves can delver astoundingly high currents with no problem. Its the BMS fitted in series with them that so heavily limits the current capability. 

[Tony1]

5 minutes ago, MtB said:

 

Being pedantic but practical, the lithium cells themselves can delver astoundingly high currents with no problem. Its the BMS fitted in series with them that so heavily limits the current capability. 

 

I've seen in theory that lithiums can deliver very high currents, but part of me always stops and wonders....

 

 

 

[MtB]

4 minutes ago, Tony1 said:

 

I've seen in theory that lithiums can deliver very high currents, but part of me always stops and wonders....

 

 

Whether or not it is safe, depends on the installation design and workmanship, and the BMS 

[Tony1]

25 minutes ago, magnetman said:

Lithium Titanate batteries have very high C rates. 

 

Worth considering. 10C is doable. 

 

Bimble were claiming they were going to carry them but not sure of they have them or not. 

 

I'd prefer to see a smaller bank of higher discharge batteries rather than a larger bank of lower discharge batteries. 

 

A few people have built batteries using the cylindrical YinLong cells but these are often re-wrapped used cells from chinese electric buses. 

 

Amazing capability these things have and they are very safe. 

Bimble 

 

https://www.bimblesolar.com/batteries/lto-longlife-lithium-batteries

 

Not cheap! 

 

 

A 2Kwh 48v module can discharge 150a which is 7200w. 

 

I think they are doing the BMS as an external unit which is sensible as the batteries themselves are liable to last longer than the electronics. 

 

some suggestions of 20,000 cycles for these which is quite useful for something like cooking. 

 

It feels like I read headlines about some new type of battery technology every month or two, and each one makes bigger claims than the one before. 

I'm half expecting for the next big battery technology to be hybrid lithium-gerbil cells (as in the small mammal).

But the thing is that I rarely hear about them again after the initial headline.

So I just assumed it was mostly baloney and hype, and that LiFeP04 would continue as the best option for at least another decade. 

But not so- lithium titanate is actually a thing, as in people will be actually be selling them to actual people, some time this year. 

If I understand it right they seem to be at least twice the price of equivalent LiFeP04 batteries, but Bimble are claiming 30,000 cycles, which I guess means they will last almost ten times longer than LiFeP04's right? 

So they are still good value, as long as you intend to cruise your boat for the next millenium or so.

We just need people to live a bit longer now, so we can enjoy the benefits of these immortal batteries. 

 

Edited March 4, 2023 by Tony1

[magnetman]

LTO have been around for ages powering electric buses..

The reason I think the cycle life is interesting is because you could do multiple charge and discharge per day. This would work well for electric cooking which is operating from batteries charged by solar or diesel generator. 

 

Fast discharge of a small battery, fast recharge of a small battery. 

 

 

[Tony1]

1 minute ago, magnetman said:

LTO have been around for ages powering electric buses..

 

I really should get out more

 

[magnetman]

At the end of the day you can only get out what you put in so having a larger bank and doing the same discharge will still result in the same input requirement. 

Only time when a bigger bank makes sense, if the services arrr being used every day, is if you have a ridiculously large solar array or mains electric availability from time to time .

[MtB]

33 minutes ago, magnetman said:

LTO have been around for ages powering electric buses..

The reason I think the cycle life is interesting is because you could do multiple charge and discharge per day. This would work well for electric cooking which is operating from batteries charged by solar or diesel generator. 

 

Fast discharge of a small battery, fast recharge of a small battery. 

 

 

 

Of more interest is whether overcharging wrecks them like LiFePO4, or if they are tolerant of a charging current at 100% SoC. 

 

And if the cell voltages can add up to 12v. 

 

 

[magnetman]

1 minute ago, MtB said:

 

Of more interest is whether overcharging wrecks them like LiFePO4, or if they are tolerant of a charging current at 100% SoC. 

 

And if the cell voltages can add up to 12v. 

 

 

I have some 40Ah 6S LTO modules which can go up to 16.8v. I charge mine to 15.2v which is about 85%. Not ideal for 12v systems but it does work. Inverter cutouts are usually 15.5-16v. 

 

LTO lends itself better to 24 or 48v systems due to the individual cell voltage. 

 

Mr Fish wants a 48v system which was why I mentioned them on this thread.

 

I mostly use mine for electric canoe which has a 12v brushed motor which can happily tolerate 15v. 

 

 

[MrFish]

The specs on the Bimble LTOs does look very good. Though i do think the BMS fitted will be the most significant limiting factor. The cost is not listed but i rather suspect i will have to sell my grand mother into slavery to be able to afford them! my budget is about £7k.

[magnetman]

It does say £2k for a 2 Kwh 48v battery.... £1 per wh. expensive !

 

I picked up some bankrupt stock LTO bus batteries for about 15p per wh. 

 

They don't have BMS or balancing. It is interesting looking at some other forums as people who use LTO sometimes suggest they don't need balancing. 

 

Seems odd but it is possible. I've also run one of mine right down to about 6v and it seems fine. Maybe it won't last. They may just be very abuse tolerant. Mine were cheap enough not to worry but if spending a lot of money you would want to have a proper bms and yes this will limit the output. 

 

 

 

[MtB]

2 minutes ago, magnetman said:

Mine were cheap enough not to worry but if spending a lot of money you would want to have a proper bms and yes this will limit the output. 

 

I'm not sure that logic holds good. 

 

One needs to be thinking about the replacement cost, not what one paid for them when considering whether to look after them carefully, or not bovver. 

 

Can you get replacements for 15p/kWh or would they now cost you £1?

 

[MrFish]

at £1/Wh is about 4 times the cost of the Fogstar.  Would definitely need a BMS. I wouldn't want to risk overcharging or un-monitored heat beat up. I cant imagine any insurance company would be happy without. I did see on the Bimble page that their LTO batteries have 150A per module, max 7200W 

[magnetman]

I can't get replacements for them. They are experimental. If they degrade fast then so what just do something else. They are working at the moment which is all that is ultimately relevant. 

 

They were cheaper than good AGM batteries so might as well see what happens. They might last ten years. 

 

I only charge and discharge them at 1C regularly. 

If you were doing a lot of hard discharges it would probably be good to have BMS yes. 

 

6 minutes ago, MrFish said:

at £1/Wh is about 4 times the cost of the Fogstar.  Would definitely need a BMS. I wouldn't want to risk overcharging or un-monitored heat beat up. I cant imagine any insurance company would be happy without. I did see on the Bimble page that their LTO batteries have 150A per module, max 7200W 

Yes the Bimble batteries are very expensive. 

 

The point is, to me, that you would not need to get a big bank because it can do the discharge job with a smaller bank. 

 

You still have to put the energy back into the batteries regardless of how big the battery bank is. 

 

If you have occasional mains or a solar array which is always providing more than your daily usage then yes a bigger bank makes sense but other than that it doesn't make sense. 

 

 

[IanD]

2 hours ago, MrFish said:

Yeah the hobs will just keep pumping out power because it has no idea what temperature the food needs to reach. Whereas the oven is a contained insulated box that will turn off the heating elements when it reaches the set temperature. I think this is why the oven manufacturers look at kwh averages but they are still obliged to tell you the max current draw.  Its looking at all those potential peak loads that i am being careful to calculate.

 

The biggest down side of the lithiums that i can see is the max current draw. If you are lucky enough to have shore power then the mulitplus will balance where it draws power from, but if you cant do that then the batteries need to have a higher max discharge current or have a balanced parallel system. 

 

So long as you can deliver the peak power needed, a hob can use less energy than an oven...

 

An induction hob with all four rings on full can indeed take 7kW or so -- but you very rarely have all four rings on at the same time, and if you do it's not for very long. Similarly you rarely have even one ring (usually a couple of kW, maybe three on "boost") on full power for very long, things that need to be that hot cook fast, and anything on the hob for a long time is likely to be simmering at a few hundred watts. Ovens can be on for several hours, but again like the rings they turn the power down when hot -- but if anything still use more energy.

 

Also the actual energy use can be much less than you think, see here -- typical numbers are 0.5kWh/meal for an induction hob, 1kWh/meal for an oven.

 

https://www.confusedaboutenergy.co.uk/household-energy-costs/buying-household-appliances/cookers.php

[magnetman]

Good to get some figures. 

 

So if you had a 2kwh battery you could cook a meal using 1Kwh and if you replace the power at 10A @48v it would take just over two hours to get the power back in. 

 

This is why I don't think an excessively large battery is needed but high cycle life would be desirable. You could be doing several cycles per day. 

 

 

Edited March 4, 2023 by magnetman
Edit to remove accidental mild sex references

[MrFish]

The problem is i have to go out to work. So there are times when it is too late in the day to run a generator. So i want the bank big enough to allow several days go by without running a gen or engine. The Fogstar 560ah is rated at 3500 cycles at 100%DoD. I know this is dependant on ambient temps but given that it is a liveaboard the temps will never get very low. 

36 minutes ago, IanD said:

 

So long as you can deliver the peak power needed, a hob can use less energy than an oven...

 

An induction hob with all four rings on full can indeed take 7kW or so -- but you very rarely have all four rings on at the same time, and if you do it's not for very long. Similarly you rarely have even one ring (usually a couple of kW, maybe three on "boost") on full power for very long, things that need to be that hot cook fast, and anything on the hob for a long time is likely to be simmering at a few hundred watts. Ovens can be on for several hours, but again like the rings they turn the power down when hot -- but if anything still use more energy.

 

Also the actual energy use can be much less than you think, see here -- typical numbers are 0.5kWh/meal for an induction hob, 1kWh/meal for an oven.

 

https://www.confusedaboutenergy.co.uk/household-energy-costs/buying-household-appliances/cookers.php

So what battery bank have you gone for on your new build?

[magnetman]

Fogstar seem to put heating pads in a lot of their products which is sensible. 

 

 

[MrFish]

If you haven't seen it before then take a look at this strip down of a Fogstar drift lithium. Seems to be very well constructed

 

 

This next video was a bit of an eye opener for me. It appears to show that the BMS max discharge limit can be significantly exceeded. Not something i was aware of. I had always assumed the BMS would kill the power if max draw was exceeded.

 

 

[IanD]

1 hour ago, MrFish said:

The problem is i have to go out to work. So there are times when it is too late in the day to run a generator. So i want the bank big enough to allow several days go by without running a gen or engine. The Fogstar 560ah is rated at 3500 cycles at 100%DoD. I know this is dependant on ambient temps but given that it is a liveaboard the temps will never get very low. 

So what battery bank have you gone for on your new build?

48V 700Ah -- 16 series Winston cells like these, with a custom BMS integrated over CANbus with the Victron inverter/charger/MPPT:

 

https://shop.gwl.eu/Winston-40Ah-200Ah/WB-LYP700AHA-LiFeYPO4-3-3V-700Ah.html

 

But don't forget this is a series hybrid boat, with a 9kVA generator and a 15kW motor (continuous rating -- 25kW peak), so it needs a hefty battery bank... 😉

Edited March 4, 2023 by IanD