Lithium battery abuse

[Tony1]

6 minutes ago, George and Dragon said:

The issue you would face is power dissipation: P=I^2/R. What kind of resistance value do you have in mind? For 750W you'd be looking at just 0.3 ohms

 

 

To be honest I dont know what kind of resistance would be needed. My only knowledge of electrics is that thing of watts being equal to amps x volts. So my rough calculation was 13 volts times say 50 amps, equals a heatsink or resistor of about 700 watts? 

You have to imagine that there is going to be a cheap device you can buy instead of a length of thin cable, that is actually designed to dissipate heat and limit current? 

 

I think I prefer the idea of purpose designed bit of kit instead of say 5 metres of loosely bundled wire. 

 

Edited February 16, 2022 by Tony1

[George and Dragon]

And if you site the resistor sensibly you might get to use the 'waste' heat.

 

ETA If you're not already running the engine it could be in the cauliflower.

Edited February 16, 2022 by George and Dragon

[Tony1]

6 minutes ago, George and Dragon said:

And if you site the resistor sensibly you might get to use the 'waste' heat.

 

ETA If you're not already running the engine it could be in the cauliflower.

 

Having the heatsink resistor thing inside the cabin is probably not a bad shout to be fair, but as an electrical novice I would want to keep it simple. 

My thinking was it would be a resistor or something placed within a foot or two of the alternator, connected by a 70mm cable that can handle a bit of heat. 

The idea would be that the excess heat would build up in the resistor thing, rather than in any of the connecting cables before or after it.

Dr Bob and the other users of this setup report no excessive heat in the cable, so I'm probably concerned about a non-issue.

Its just that when I tried it, the long thin wire did get a bit too hot for my liking. But that said, my trial run was when I was charging the lithiums via an A2B charger, and without a lead acid battery in between.  

 

But it does look like Dr Bob and the others have given new lithium adopters an affordable and safe install method to use these brilliant batteries. 

 

[nicknorman]

1 hour ago, Tony1 said:

 

To be honest I dont know what kind of resistance would be needed. My only knowledge of electrics is that thing of watts being equal to amps x volts. So my rough calculation was 13 volts times say 50 amps, equals a heatsink or resistor of about 700 watts? 

You have to imagine that there is going to be a cheap device you can buy instead of a length of thin cable, that is actually designed to dissipate heat and limit current? 

 

I think I prefer the idea of purpose designed bit of kit instead of say 5 metres of loosely bundled wire. 

 

As you say, watts = volts x amps. But the volts is the voltage dropped across the resistor, not the system voltage. So if you wanted to drop 0.3v at 50A it would be 15w. And the resistor would be 0.006 ohms.

[MarkH2159]

1 hour ago, Tony1 said:

 

Apologies if I've missed the detail, I'm rubbish with electrics- but how is the current delivered to the lithium battery? 

The way I've read that, it sounds as if the AGM goes straight to the inverter. 

The Alternator is connected to the AGM which is connected to the Inverter which is connected to the Lithium. Basically all three units are in parallel.

The reason for this is threefold...

 

As Lithiums do not like temperature change and can be damaged if attempts are made to charge at very low temperatures, the BMS is programmed to cut off the Lithium at 5C.

By putting the Lithium inside, in the same locker as the Inverter, it overcomes the possibility of it ever suffering freezing temperatures.

 

Secondly it extends the amount of wiring between the alternator and the Lithium thereby introducing a resistance which artificially reduces the lithium ability to suck too much charge from the alternator.

 

Thirdly as the Lithium is providing most of the power demand of the inverter, having it close by on short cables reduces any cabling losses.

 

By using the 'long wire' and 10mm2 cable I am still connecting the alternator with a wire of sufficient size to handle its total rated output of 70 amps but the resistance induced automatically cuts the amperage. 

This means that there is no need for any kind of ballast resistance or other add in that could complicate things and produce heat, thereby wasting energy.

 

 

1 hour ago, Tony1 said:

 

 

 

Edited February 16, 2022 by MarkH2159

[Tony1]

13 minutes ago, MarkH2159 said:

The Alternator is connected to the AGM which is connected to the Inverter which is connected to the Lithium. Basically all three units are in parallel.

The reason for this is threefold...

 

As Lithiums do not like temperature change and can be damaged if attempts are made to charge at very low temperatures, the BMS is programmed to cut off the Lithium at 5C.

By putting the Lithium inside, in the same locker as the Inverter, it overcomes the possibility of it ever suffering freezing temperatures.

 

Secondly it extends the amount of wiring between the alternator and the Lithium thereby introducing a resistance which artificially reduces the lithium ability to suck too much charge from the alternator.

 

Thirdly as the Lithium is providing most of the power demand of the inverter, having it close by on short cables reduces any cabling losses.

 

By using the 'long wire' and 10mm2 cable I am still connecting the alternator with a wire of sufficient size to handle its total rated output of 70 amps but the resistance induced automatically cuts the amperage. 

This means that there is no need for any kind of ballast resistance or other add in that could complicate things and produce heat, thereby wasting energy.

 

 

 

 

Thanks for explaining, and can I just check- are you using an A2B charger, or just running straight from the alternator to the AGM?

 

Forgive my questioning, I'm trying to get an idea of it in my head so that I can explain it to people that I talk to who show an interest in lithium batteries.

I sometimes mention it when I get talking about boat upgrades, and people are often very interested in lithiums, but when I talk about needing BMV712s, BEP switches, and B2B chargers, they see the cost mounting and quickly lose interest, which I think is a shame. 

 

 

 

 

 

 

Edited February 16, 2022 by Tony1

[MarkH2159]

3 minutes ago, Tony1 said:

 

Thanks for explaining, and can I just check- are you using an A2B charger, or just running straight from the alternator to the AGM?

 

Forgive my questioning, I'm trying to get an idea of it in my head so that I can explain it to people that I talk to who show an interest in lithium batteries.

I sometimes mention it when I get talking about boat upgrades, and people are often very interested in lithiums, but when I talk about needing BMV712s, BEP switches, and B2B chargers, they see the cost mounting and quickly lose interest, which I think is a shame. 

 

 

 

 

 

 

Alternator is direct to AGM via 10mm2 cable 2m long.

No fancy B2B or DC to DC, no switches etc.

The long wire method proves them all to be totally unnecessary and a waste of money.

Keep it simple is always the best way.

 

[MoominPapa]

30 minutes ago, MarkH2159 said:

By using the 'long wire' and 10mm2 cable I am still connecting the alternator with a wire of sufficient size to handle its total rated output of 70 amps but the resistance induced automatically cuts the amperage. 

This means that there is no need for any kind of ballast resistance or other add in that could complicate things and produce heat, thereby wasting energy.

The long wire is a ballast resistance and will produce heat. I suggest not bundling it up or installing is in enclosed compartments or touching flamable material.

 

MP.

[MarkH2159]

58 minutes ago, MoominPapa said:

The long wire is a ballast resistance and will produce heat. I suggest not bundling it up or installing is in enclosed compartments or touching flamable material.

 

MP.

You speak from experience..?

There is no discernable extra heat produced as the increased resistance is actually minimal.

It is basically just enough to cause the regulator to drop the output of the alternator.

 

I repeat, no heat, no insulation melting, no sign of any such issues.

It is in a single coil, held by small zip ties, in an enclosed engine compartment.

 

Nothing is going to happen because 10mm2 cable can easily handle the total output of the alternator which is 70 amps.

Edited February 16, 2022 by MarkH2159

[Dr Bob]

3 hours ago, MarkH2159 said:

The Daly BMS is set to cut off at a pack total voltage of 14v which keeps the LiFePO4 slightly under 100% full and quite happy.

.

 

1 hour ago, Tony1 said:

 

 

 

But it does look like Dr Bob and the others have given new lithium adopters an affordable and safe install method to use these brilliant batteries. 

 

 

Yes they are safe but it looks like some people are not listening. Mark, lithium's - whatever the chemistry - are not ever happy at slightly under 100% full. It is not a good idea to charge to that level all the time and keep them there. The company I am a director of does a lot of Li battery testing - to destruction - and are engaged in a number of Eu consortium programmes on air transport of lithium batteries. The power in a 100% charged Li battery is huge. That is when problems happen. Yes, you can go to 100% now and again but that is not the way to treat them, and they certianly shouldnt be left full.

I never charge my car to 100% and certainly never leave it above 90% - that is what the manufacture says....for a reason. We test them. We know! Trust me...I'm a muppet doctor.

Edited February 16, 2022 by Dr Bob

[MarkH2159]

39 minutes ago, Dr Bob said:

 

 

Yes they are safe but

??

 

The reason for the 14v Charge cut off is so that the Lithiums do not actually reach their full 100% charge capacity. Unlike lead Acids the LiFePO4s do not fair well being fully charged all the time.

 

Similarly the low voltage discharge cut off is set to 12v so they never get to being totally flat either.

 

Using the range 14v to 12v keeps the Lithium cells running at between 90 and 10% charge, a range in which they are both happy and safe and gives me a usable 80% of the 280AH total.

 

Do not confuse LiFePO4 with Lithium Ion batteries.

LiFePO4s are perfectly safe and happy at under 100% charge state.

Edited February 16, 2022 by MarkH2159

[MoominPapa]

44 minutes ago, MarkH2159 said:

You speak from experience..?

There is no discernable extra heat produced as the increased resistance is actually minimal.

It is basically just enough to cause the regulator to drop the output of the alternator.

 

I repeat, no heat, no insulation melting, no sign of any such issues.

It is in a single coil, held by small zip ties, in an enclosed engine compartment.

 

Nothing is going to happen because 10mm2 cable can easily handle the total output of the alternator which is 70 amps.

 

I believe you, but in that case a suitable ballast resistor would stay cool too. If has the same effect it has the same resistance and dissipates the same amount of power. BTW have you actually calculated what the power dissipation is?

 

I can't help thinking that all this effect with B2Bs and bits of wire are avoiding the real solution, which is properly implemented alternator regulator.

 

MP.

[Tony1]

3 minutes ago, MoominPapa said:

 

I can't help thinking that all this effect with B2Bs and bits of wire are avoiding the real solution, which is properly implemented alternator regulator.

 

MP.

 

I'm not a great fan of B2Bs or indeed long wire solutions, but people have to work within their budgets, and as long as these solutions are safe, they do at least meet the criteria of being affordable, and they allow more people to enjoy the benefits of lithiums. 

 

I would agree that an alternator regulator is the best solution, as long as you can afford it, but I had one quote of around £550 to supply and fit one, whereas a B2B is £300, and you can fit it yourself- and the long wire is much cheaper still. 

 

I feel we should all encourage affordable solutions, as long as they are safe. Plus if folks save money on the battery system, some of them might have cash left to spend on solar panels, and that way get even more benefit from the lithiums.

 

 

[MarkH2159]

6 minutes ago, MoominPapa said:

 

I believe you, but in that case a suitable ballast resistor would stay cool too. If has the same effect it has the same resistance and dissipates the same amount of power. BTW have you actually calculated what the power dissipation is?

 

I can't help thinking that all this effect with B2Bs and bits of wire are avoiding the real solution, which is properly implemented alternator regulator.

 

MP.

I have no need to calculate the power dissipation.

You seem to think the unused alternator power is being somehow redirected to create heat, but that is not the way it works at all.

 

I do know that the load on my alternator is reduced, therefore the heat it produces is less and life of unit and belt is increased.

 

I also know that B2B units cost a lot of money and often generate a lot of heat and are another complicated electronic gizmo prone to failure.

 

I also know that at a cost of around £4 I have put in a simple and safe method of achieving the necessary.

 

Changing the alternator or its regulator is definitely not necessary and I am not the only one who has proved it.

[MarkH2159]

2 hours ago, nicknorman said:

As you say, watts = volts x amps. But the volts is the voltage dropped across the resistor, not the system voltage. So if you wanted to drop 0.3v at 50A it would be 15w. And the resistor would be 0.006 ohms.

Spot On !!!

And at 0.006 ohms the extra heat created would be........Not Discernable

[MtB]

Although easily solved, none of the above addresses the need of Li batts to be cycled from near-fully charged to near-fully discharged, rather than kept near-fully charged all the time. 

 

Or does the team disagree?

 

 

 

 

[Tony1]

26 minutes ago, MtB said:

Although easily solved, none of the above addresses the need of Li batts to be cycled from near-fully charged to near-fully discharged, rather than kept near-fully charged all the time. 

 

Or does the team disagree?

 

 

 

 

 

The experts will give a proper answer on this Mike, but I think there are cheap tweaks you could do to the basic setup to help ensure the lithiums get enough exercise, so to speak. 

I think Dr Bob mentioned that the lithiums can be isolated from the lead acids when they get to 90% full (or whatever the day to day 'fill' limit is). 

I think this is via a BEP type switch that works automatically, but you could use a cheap manual switch if it is handy to access (and some cheaper battery monitors will have an alarm sound to warn you when the desired voltage or SoC is reached).

That way you could save the £200 on a motorised disconnect switch, and another £150 or more on a BMV712.

 

I would guess that you could leave the lithiums separated from the lead acids for most of the time, and let them run down their SoC or voltage to the set lower limit as often as you feel is best for them, and reconnect them to the lead acids when you want to charge again. Would that work?

 

Edited February 16, 2022 by Tony1

[nicknorman]

8 hours ago, MtB said:

Although easily solved, none of the above addresses the need of Li batts to be cycled from near-fully charged to near-fully discharged, rather than kept near-fully charged all the time. 

 

Or does the team disagree?

 

I agree, but I think it depends on what sort of boater you are. If you are mostly static then it’s easy to arrange for the batteries to not be kept in a high state of charge for long periods - you simply turn of the engine or generator or solar at the appropriate time. For a leisure boat where most days are long cruising days it needs to be better thought out, hence our system which stops charging at the specified SoC.

[nicknorman]

8 hours ago, MarkH2159 said:

I have no need to calculate the power dissipation.

You seem to think the unused alternator power is being somehow redirected to create heat, but that is not the way it works at all.

 

I do know that the load on my alternator is reduced, therefore the heat it produces is less and life of unit and belt is increased.

 

I also know that B2B units cost a lot of money and often generate a lot of heat and are another complicated electronic gizmo prone to failure.

 

I also know that at a cost of around £4 I have put in a simple and safe method of achieving the necessary.

 

Changing the alternator or its regulator is definitely not necessary and I am not the only one who has proved it.

I think MP’s point was that one could either use a length of wire, or a series resistor, both of which have the identical effect of dropping some voltage between alternator and batteries so much less current flows. Some power is dissipated n the process, but not a lot and certainly not the “missing” output from the alternator. Both the cable and the resistor generate some heat, in the cable it would be less noticeable due to the heat being spread out over a much bigger area.

[Alan de Enfield]

 

 

I think this thread has just re-inforced my thoughts that the use of lithiums is still too far away for me to consider.

 

To be 'an early adopter' it seems you need to be an electronics engineer or a 'millionare'.

 

There seems little point in having a big aternator and then throttling it back to 50%, and then using a B toB charger and throttling it back even more, then adding in a resistance wire to drop the voltage.

 

You seem to be generating a lot of heat, and doing away with the main advantage of being able to charge your battery bank in 'a couple of hours', & then the advice you should only use 20% - 80% of capacity .......................

 

I understand FLA's they understand me and the system currently works.

[Slow and Steady]

18 minutes ago, Alan de Enfield said:

 

 

I think this thread has just re-inforced my thoughts that the use of lithiums is still too far away for me to consider.

 

To be 'an early adopter' it seems you need to be an electronics engineer or a 'millionare'.

 

There seems little point in having a big aternator and then throttling it back to 50%, and then using a B toB charger and throttling it back even more, then adding in a resistance wire to drop the voltage.

 

You seem to be generating a lot of heat, and doing away with the main advantage of being able to charge your battery bank in 'a couple of hours', & then the advice you should only use 20% - 80% of capacity .......................

 

I understand FLA's they understand me and the system currently works.

Depends on what you have to start with? It appears that if you have a travel power for example charging becomes more simple.

[Alan de Enfield]

5 minutes ago, Slow and Steady said:

Depends on what you have to start with? It appears that if you have a travel power for example charging becomes more simple.

 

I have 6x 220Ah FLA's and two 70 amp alternators, We cruise most days for several hours and have a Jennifer on board if we decide not to move for a few days.

[nicknorman]

23 minutes ago, Alan de Enfield said:

 

I have 6x 220Ah FLA's and two 70 amp alternators, We cruise most days for several hours and have a Jennifer on board if we decide not to move for a few days.

Your situation is quite similar to ours in terms of cruising pattern, although we only had 450Ah LA batteries. It was certainly hard for me to justify switching to Li on grounds of “need”, it was more “out of interest” and the supporting tech, a lockdown project. But I have to say I am muchly impressed by the Li, in particular the ability to maintain full charge current until about 99% SoC, and the absence of need to worry about sulphation / partially charging. And as a consequence, outrageous profligacy in the use of electrical power off grid that is enabled!

 

Getting away from the annoyance of the lonnnnnggggg  sllloooowwwwww charge of the latter stages of LA charging is a blessing!

[Dr Bob]

12 hours ago, MarkH2159 said:

Do not confuse LiFePO4 with Lithium Ion batteries.

LiFePO4s are perfectly safe and happy at under 100% charge state.

 

The comments that some uniformed people make on here is mindblowing. Where do you get that information from? At best it is misleading and at worst DANGEROUS! If you had said 'mostly safe and happy under 90%' then I would agree.

 

See the following link to a thread posted 3 years ago. At that time there was certianly not enough data to support your claim. Our company has been working on the thermal runaway issues since then (and including LiFePO4 cells) helping develop a pre theremal runaway warning technique. I consider myself a technical expert on this type of battery chemistry, even if I cant design the electical system to control alternator charge.

 

 

I would recommend MarkH2159 read that thread and the associated links.

 

Anyone considering installing a home brew system of LiFePO4s needs to do a safety assessment on what they are installing and the starting position for that is to as much as possible keep away from 100% charging. I use 90% as my upper limit over which the auto disconnect works and my 'operating proceedure' says only go to 100% when I am personally in manual control of the voltage and current. Keeping LiFePO4s at 90% or below is very very unlikely to present an ignition hazard on well trusted cells (it is not going to happen on a canal boat). The risk is much higher at 99%.

There is very little point in taking these to 99%. The whole idea is that you dont need to fully charge. Why risk safety when thermal runaways are a risk?

[Idle Days]

11 hours ago, MtB said:

Although easily solved, none of the above addresses the need of Li batts to be cycled from near-fully charged to near-fully discharged, rather than kept near-fully charged all the time. 

 

Or does the team disagree?

 

 

 

 

MY batteries are exercised every time I tie up for the night.