An affordable way to fit Lithium Batteries?

[peterboat]

15 minutes ago, nicknorman said:

The “low tech is best” argument was presented each time technical progress was in the offing. From the invention of the weaving machine onwards. Why have light bulbs, especially LED ones with electronics inside, when a candle is perfectly capable of providing light? Far less to go wrong.

 

Anyway I can accept that the compromises you have chosen work well for you and I am not criticising you for it. But as a technical solution I don’t feel it is optimised, and optimising it wouldn’t be that difficult (for me).

 

Just on the 80% charged thing which is bandied about a lot, are there any actual figures for this? I’m thinking that whilst one might want to routinely charge to 80%, on occasion (when planning to moor up for a few days) it would be useful to be able to get to 100%. I can’t imagine that this would have anything but the very slightest effect on battery life.

 

Oh and for us with the Iskra 175A alternator, I wouldn’t like that to have unfettered access to Li batteries - overheating issues plus load on engine and drive belt when near idle.

Solar panels are the answer if you want to moor up for a few days/weeks Nick, lovely low tech solution, I can highly recommend them.

You are right about the occasional up to 100% charge but to do that you have to have a BMS and whilst I have them I dont use them, my choice as I am happy with 80% on both domestic and drive batteries

[nicknorman]

20 minutes ago, peterboat said:

Solar panels are the answer if you want to moor up for a few days/weeks Nick, lovely low tech solution, I can highly recommend them.

You are right about the occasional up to 100% charge but to do that you have to have a BMS and whilst I have them I dont use them, my choice as I am happy with 80% on both domestic and drive batteries

Not allowed to have solar panels, they spoil the look of the boat! If we were live aboard I think I’d insist, but not worth it for a leisure boat.

[MtB]

10 minutes ago, nicknorman said:

Not allowed to have solar panels, they spoil the look of the boat!

 

Always the comedian, very funny!!

 

[peterboat]

1 hour ago, nicknorman said:

Not allowed to have solar panels, they spoil the look of the boat! If we were live aboard I think I’d insist, but not worth it for a leisure boat.

Quality semi-flexibles? you can hardly see them, and you only need 300 watts or so 400 to make it even ?

[cuthound]

36 minutes ago, peterboat said:

Quality semi-flexibles? you can hardly see them, and you only need 300 watts or so 400 to make it even ?

 

I thought the flexible solar panels were so unreliable that @matty40s now refuses to fit them for customers.

 

Pity because I also think that they are the only solar panels which don't spoil the looks of the boat.

[Dr Bob]

5 hours ago, nicknorman said:

 

 

Just on the 80% charged thing which is bandied about a lot, are there any actual figures for this? I’m thinking that whilst one might want to routinely charge to 80%, on occasion (when planning to moor up for a few days) it would be useful to be able to get to 100%. I can’t imagine that this would have anything but the very slightest effect on battery life.

 

Oh and for us with the Iskra 175A alternator, I wouldn’t like that to have unfettered access to Li batteries - overheating issues plus load on engine and drive belt when near idle.

There have been a few references saying that keeping them at 100% reduces capacity over a long period....i.e. A year and others saying that Cycle of 40-80% give maximum cycles. I am sure it's ok to take them up there, and I will do every few months a one of the papers talks about needing to do that.....but the main reason for me sticking to 80% was to preserve the cell balance which I have read many times can go out of balance if you keep charging up into the knee. I want to avoid having to balance them and it seems to be working. 

Even if you use 100Ahrs a day, with little solar, you can stay in one place for days and hardly run the engine. It's been a joy parking under trees for a few day in last weeks heat without worrying. You really don't need to go higher than 80%.

[peterboat]

2 hours ago, cuthound said:

 

I thought the flexible solar panels were so unreliable that @matty40s now refuses to fit them for customers.

 

Pity because I also think that they are the only solar panels which don't spoil the looks of the boat.

I have 9 that are over 6  years old and still working ok, I removed them to fit larger 300 plus watt rigid panels for the electric motor, I have tested them and they all still work ok so I am fitting them to the bathtub, they are quality panels from the USA though

[nicknorman]

3 minutes ago, Dr Bob said:

There have been a few references saying that keeping them at 100% reduces capacity over a long period....i.e. A year and others saying that Cycle of 40-80% give maximum cycles. I am sure it's ok to take them up there, and I will do every few months a one of the papers talks about needing to do that.....but the main reason for me sticking to 80% was to preserve the cell balance which I have read many times can go out of balance if you keep charging up into the knee. I want to avoid having to balance them and it seems to be working. 

Even if you use 100Ahrs a day, with little solar, you can stay in one place for days and hardly run the engine. It's been a joy parking under trees for a few day in last weeks heat without worrying. You really don't need to go higher than 80%.

Well obviously it depends on your energy usage vs battery bank capacity. We seem to use about 150 AH between stopping in the afternoon/evening, and starting off again in the late morning. 24 hrs would probably see it approaching 200AH.

[Dr Bob]

5 minutes ago, nicknorman said:

Well obviously it depends on your energy usage vs battery bank capacity. We seem to use about 150 AH between stopping in the afternoon/evening, and starting off again in the late morning. 24 hrs would probably see it approaching 200AH.

Assume you have 480Ahrs.

Run the engine 1 hr per day to heat the water and put 50A back in.

Start at 400Ahrs. 80% SoC.

Use 200 Ahrs every 24 hrs so net loss is 150 Ahrs. 

You can stop for 48 hrs and be down to 100Ahrs. No problem. 

.......and the big benefit is the next day you don't need to motor for 10 hrs. A couple is fine. No need to ever get back to full.

 

Add some solar and you you can stop for a week.

 

[nicknorman]

3 minutes ago, Dr Bob said:

Assume you have 480Ahrs.

Run the engine 1 hr per day to heat the water and put 50A back in.

Start at 400Ahrs. 80% SoC.

Use 200 Ahrs every 24 hrs so net loss is 150 Ahrs. 

You can stop for 48 hrs and be down to 100Ahrs. No problem. 

.......and the big benefit is the next day you don't need to motor for 10 hrs. A couple is fine. No need to ever get back to full.

 

Add some solar and you you can stop for a week.

 

Yes fine but 480AH of Li is quite a big bank! Yes obviously I get the fast charging thing, even faster with our 175A alternator. Plus travelpower feeding 100A charger. So one hour at 275A will put in more than a day’s worth of charge. Or 30 mins worth plus the Mikuni on for a bit to heat up the water.

 

Yes I get it. But we don’t have room for 450AH of Trojans plus 480AH of lithiums!

 

The other point of course is that AH is not a measure of energy. 100AH of Li is worth more than 100AH of LA, due to the higher voltage of the former.

[dmr]

21 minutes ago, Dr Bob said:

Assume you have 480Ahrs.

Run the engine 1 hr per day to heat the water and put 50A back in.

Start at 400Ahrs. 80% SoC.

Use 200 Ahrs every 24 hrs so net loss is 150 Ahrs. 

You can stop for 48 hrs and be down to 100Ahrs. No problem. 

.......and the big benefit is the next day you don't need to motor for 10 hrs. A couple is fine. No need to ever get back to full.

 

Add some solar and you you can stop for a week.

 

What you have done is very interesting and I am watching closely   but I suspect you have over stated the downside of LAs. Like Nick we can easily put in 100Ah with an hour of engine running, and it makes hot water and runs the washing machine via the TravelPower at the same time. I also believe (well actually I know from first hand experience over several years) that we only need to fully charge the Trojans once every few weeks in order to prevent sulphation so this fits in easily with boating. Lithiums still look very tempting but I can't see the big advantage over LAs to justify the cost. If we stay in one place for more than two days we run out of hot water before we run out of leccy.

 

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

[MtB]

23 minutes ago, nicknorman said:

Yes fine but 480AH of Li is quite a big bank!

 

Not sure where you get that idea from. My 200AH 24V bank (which could be re-wired to give 400AH at 12V) is about the size of an old skool desktop computer. Probably half the volume and a third of the weight of your 400AHs of Trojan battery.

 

And you don't need 400AH of LA in parallel, 100AH will do the job. 

 

 

 

[nicknorman]

10 hours ago, Mike the Boilerman said:

 

Not sure where you get that idea from. My 200AH 24V bank (which could be re-wired to give 400AH at 12V) is about the size of an old skool desktop computer. Probably half the volume and a third of the weight of your 400AHs of Trojan battery.

 

And you don't need 400AH of LA in parallel, 100AH will do the job. 

 

 

 

By “big” I meant in terms of AH and cost.

[MtB]

1 minute ago, nicknorman said:

By “big” I meant in terms of AH and cost.

 

Ah, I thought you meant you were concerned that you have nowhere to put it!

 

[nicknorman]

2 minutes ago, Mike the Boilerman said:

 

Ah, I thought you meant you were concerned that you have nowhere to put it!

 

Well there would be with the 450AH of Trojans, but as you say no need to retain all of that.

Or in my case, none of that!

[Alfabiker]

Dr Bob:

I am very interested in your idea of the simple hybrid system as I can see a lot of advantages in it.  I presently have 3 Exide 115ah SLA's in the domestic bank of my boat (and 300w of solar) and I could do with a bit more capacity, so I was thinking of adding a LiFePO of say 120Ah in parallel, hopefully with some suitable controls, but I have a couple of basic concerns: 

(1) You mention that you can run the combined bank down to 12.0 volts, but this seems a bit low for the recommended working range of the LiFePO batteries - some people even talk about disconnecting them at 12.7-12,8v (I try not to let my SLA bank run down to less than 12,2v off load anyway)? and

(2) my boat engine has a 70A alternator for the leisure batteries (as well a separate smaller one for the starter battery) which charges the existing bank very well, but do I run the risk of overloading it with the addition of the one extra Li battery or should I get away with that do you think?

 

Thanks for your thoughts in advance!

[Dr Bob]

1 hour ago, Alfabiker said:

Dr Bob:

I am very interested in your idea of the simple hybrid system as I can see a lot of advantages in it.  I presently have 3 Exide 115ah SLA's in the domestic bank of my boat (and 300w of solar) and I could do with a bit more capacity, so I was thinking of adding a LiFePO of say 120Ah in parallel, hopefully with some suitable controls, but I have a couple of basic concerns: 

(1) You mention that you can run the combined bank down to 12.0 volts, but this seems a bit low for the recommended working range of the LiFePO batteries - some people even talk about disconnecting them at 12.7-12,8v (I try not to let my SLA bank run down to less than 12,2v off load anyway)? and

(2) my boat engine has a 70A alternator for the leisure batteries (as well a separate smaller one for the starter battery) which charges the existing bank very well, but do I run the risk of overloading it with the addition of the one extra Li battery or should I get away with that do you think?

 

Thanks for your thoughts in advance!

My system has never been below 12.7V since putting in the Li's so have no experience of voltages down the bottom end. As I understand it LiFePo4s can go down to 3.0V per cell so 12V in a 4 cell system without getting into the bottom knee. If you dont go below 12.2V then you should be fine. The one thing to watch though is how you decide to isolate the bank on high and low voltage. If you are down around the 12.3 - 12.4V and then put the nesspresso machine on, you will go sub 12.0V for a minute or so. If you have your low voltage cut off at 12.2V, that will then be triggered and the Li's isolated. You may want to play around with the lower voltage cut off or the time delay.

Alternator charging Li's is a tricky one. I am very lucky as I have a Sterling AtoB (my alternator only manages 13.9V max....and I got the AtoB to get it up to 14.2v) which does a great job on the USA gel setting cutting back the current as I get up to 80% SoC. I therefore never get up to 100% on the alternator. My strategy is never trigger the overvoltage auto disconnect but this is the failsafe if your alternator is putting too much voltage in. In practice, I know at the start of the day how much capacity I need to put back in and so can quickly estimate how many engine hours I can do before I am full. I never have got to 100% on the daily alternator charge (90A alternator). If you are worried over this then try it and see how you get on. It is easy to isolate the Li bank if it does get full.

[peterboat]

3 hours ago, Dr Bob said:

My system has never been below 12.7V since putting in the Li's so have no experience of voltages down the bottom end. As I understand it LiFePo4s can go down to 3.0V per cell so 12V in a 4 cell system without getting into the bottom knee. If you dont go below 12.2V then you should be fine. The one thing to watch though is how you decide to isolate the bank on high and low voltage. If you are down around the 12.3 - 12.4V and then put the nesspresso machine on, you will go sub 12.0V for a minute or so. If you have your low voltage cut off at 12.2V, that will then be triggered and the Li's isolated. You may want to play around with the lower voltage cut off or the time delay.

Alternator charging Li's is a tricky one. I am very lucky as I have a Sterling AtoB (my alternator only manages 13.9V max....and I got the AtoB to get it up to 14.2v) which does a great job on the USA gel setting cutting back the current as I get up to 80% SoC. I therefore never get up to 100% on the alternator. My strategy is never trigger the overvoltage auto disconnect but this is the failsafe if your alternator is putting too much voltage in. In practice, I know at the start of the day how much capacity I need to put back in and so can quickly estimate how many engine hours I can do before I am full. I never have got to 100% on the daily alternator charge (90A alternator). If you are worried over this then try it and see how you get on. It is easy to isolate the Li bank if it does get full.

I have sold 4 of my LifePo4s to a friend, his alternator hands out 13.9 volts, he just uses one alternator for both banks and it's working fine the LA starter seems to provide the protection required for fast disconnect.  I have 30 x 36 volt LifePo4s for drive now which gives me over 30 KWHs, the increase in voltage and capacity should be useful over the old system. 

[nicknorman]

6 hours ago, Dr Bob said:

My system has never been below 12.7V since putting in the Li's so have no experience of voltages down the bottom end. As I understand it LiFePo4s can go down to 3.0V per cell so 12V in a 4 cell system without getting into the bottom knee. If you dont go below 12.2V then you should be fine. The one thing to watch though is how you decide to isolate the bank on high and low voltage. If you are down around the 12.3 - 12.4V and then put the nesspresso machine on, you will go sub 12.0V for a minute or so. If you have your low voltage cut off at 12.2V, that will then be triggered and the Li's isolated. You may want to play around with the lower voltage cut off or the time delay.

Alternator charging Li's is a tricky one. I am very lucky as I have a Sterling AtoB (my alternator only manages 13.9V max....and I got the AtoB to get it up to 14.2v) which does a great job on the USA gel setting cutting back the current as I get up to 80% SoC. I therefore never get up to 100% on the alternator. My strategy is never trigger the overvoltage auto disconnect but this is the failsafe if your alternator is putting too much voltage in. In practice, I know at the start of the day how much capacity I need to put back in and so can quickly estimate how many engine hours I can do before I am full. I never have got to 100% on the daily alternator charge (90A alternator). If you are worried over this then try it and see how you get on. It is easy to isolate the Li bank if it does get full.

I just bought a small 7.5AH 12v (nominal) LiFePO4 battery for a glider. The low voltage disconnect is 10v, the recommended charge voltage is 14.4v and it claims more than 3000 full depth cycle life. I therefore wonder if all this fuss about keeping between 20% and 80% SoC is actually that important. No doubt it will give better cycle life but when the worst case cycle life is already 3000, how much does it matter?

[Murflynn]

7 minutes ago, nicknorman said:

I just bought a small 7.5AH 12v (nominal) LiFePO4 battery for a glider. The low voltage disconnect is 10v, the recommended charge voltage is 14.4v and it claims more than 3000 full depth cycle life. I therefore wonder if all this fuss about keeping between 20% and 80% SoC is actually that important. No doubt it will give better cycle life but when the worst case cycle life is already 3000, how much does it matter?

blimey, that's an eye-opener; certainly confounds all the technical advice I have seen.   

are the parameters you describe built into the BMS that presumably comes with the battery?

[Alfabiker]

I was beginning to wonder about this, as you do read different suggestions everywhere you look!  My alternator which is quite new, puts out 14.4-14.5 volts maximum, and we generally cruise for only about 4-5 hours a day.  Also, I always check the voltage of my battery bank first thing in the morning when it is lowest and off load (as far as possible) to make sure it is above 12.2v.

It seems to me that if I can find a reasonably reliable BMS to take care of possible extreme circumstances - such as happened a couple of years ago when our old alternator went rogue and cooked a set of AGM batteries(!) - there shouldn't be too much of a problem.  As mentioned above I would in any case put in a manual disconnect as I don't want the Li batteries to be floated by the solar when we are away from the boat (even though float is set to 13.2v to treat the SLA's gently).

Of course there are also quite a few "drop-in" Li 12v batteries for boats etc. which claim the same sort of figures as nicknorman has quoted, but one does have to maintain a healthy level of scepticism about their built-in BMS I suspect!

[nicknorman]

27 minutes ago, Murflynn said:

blimey, that's an eye-opener; certainly confounds all the technical advice I have seen.   

are the parameters you describe built into the BMS that presumably comes with the battery?

Yes the low voltage disconnect obviously is. I should perhaps expand on the charging voltage - you charge at 14.4v until the current drops to 150mA (which is 2% of AH) then disconnect. You don’t leave it floating at 14.4v. The point really was about just how much cycle life do you lose by using more than the 60% capacity (ie 20% to 80%) that has been promoted on here.

 

The float regime is at 13.6v indefinitely. So 13.2 would be fine, provided the minimum time in bulk /absorption was set very short.

Edited September 28, 2019 by nicknorman

[nicknorman]

Incidentally I’ve been having a look at alternator regulators. This device seemed appropriate, it has a LIN interface  so a microcontroller can talk to it and send different target voltages. A home built system such as MoominP has, could determine when the SoC is approaching 100% and command the alternator regulator voltage down to 13.6 or whatever so that the alternator can continue to supply boat service loads without overcharging the Li batteries.

https://www.nxp.com/products/power-management/motor-and-solenoid-drivers/powertrain-and-engine-control/alternator-regulator-with-lin:AR6000

 

[MoominPapa]

33 minutes ago, nicknorman said:

Incidentally I’ve been having a look at alternator regulators. This device seemed appropriate, it has a LIN interface  so a microcontroller can talk to it and send different target voltages. A home built system such as MoominP has, could determine when the SoC is approaching 100% and command the alternator regulator voltage down to 13.6 or whatever so that the alternator can continue to supply boat service loads without overcharging the Li batteries.

https://www.nxp.com/products/power-management/motor-and-solenoid-drivers/powertrain-and-engine-control/alternator-regulator-with-lin:AR6000

 

Interesting. My system is now working well and no longer in development mode. at least for hardware. Maybe I need a spare boat to do R&D with!

 

Incidentally, on the subject of charging limits, I just added a mode which limits charge to 80% SoC. We've recently done a 300 mile trip at a fair clip, doing longish days every day. In that mode, the batteries were getting to 100% before lunchtime and never going below 80%. By limiting the SoC to 80%, that changes to a more battery-friendly 80%-60% range.

 

MP.

 

[nicknorman]

9 minutes ago, MoominPapa said:

Interesting. My system is now working well and no longer in development mode. at least for hardware. Maybe I need a spare boat to do R&D with!

 

Incidentally, on the subject of charging limits, I just added a mode which limits charge to 80% SoC. We've recently done a 300 mile trip at a fair clip, doing longish days every day. In that mode, the batteries were getting to 100% before lunchtime and never going below 80%. By limiting the SoC to 80%, that changes to a more battery-friendly 80%-60% range.

 

MP.

 

Yes I think my ultimate system would allow setting the SoC limit at which point charging was stopped and the alternator dropped to low 13s to supply boat loads without increasing Li battery SoC. So you would select 80% or whatever if it was just an overnight stop, and 100% if the intention was to tie up for a few days.