Lithium charging via large alternator ?

[Dr Bob]

11 hours ago, RLWP said:

 

I doubt it. Having spent some time on Melaleuca this is clearly the way to go.

 

9 minutes ago, peterboat said:

I hope you are correct, it seems at time that I am always defending my decision to go LifePo4 and always being told that they will go out of balance and destroy themselves! when in reality they dont

I think with the success that the 4 forum members have had (with no problems) and the fact that more '2nd hand' Li's will become available in the future with the rapid growth in EVs for the car and van market (thus push the price of used Li's down) will mean more of an uptake of the technology.

The benefits of Li's have really come home to me this week with very very little solar contribution since Monday (5 days ago).

There is no way though that I could justify a commercial Victron system at those silly mega prices. Has to be a DIY system.

[MoominPapa]

33 minutes ago, Dr Bob said:

 

I think with the success that the 4 forum members have had (with no problems) and the fact that more '2nd hand' Li's will become available in the future with the rapid growth in EVs for the car and van market (thus push the price of used Li's down) will mean more of an uptake of the technology.

The benefits of Li's have really come home to me this week with very very little solar contribution since Monday (5 days ago).

There is no way though that I could justify a commercial Victron system at those silly mega prices. Has to be a DIY system.

The commercial systems will drop in price, like every other new technology.

 

There may be a business opportunity is taking second-user cells from EVs and turning them into guaranteed, turnkey, boat battery systems for sale.

 

MP.

 

[Rob-M]

57 minutes ago, MoominPapa said:

The commercial systems will drop in price, like every other new technology.

 

There may be a business opportunity is taking second-user cells from EVs and turning them into guaranteed, turnkey, boat battery systems for sale.

 

MP.

 

That's what I reckon somebody needs to be doing, so between the four of you on here you need to start marketing a drop in solution.

[Dr Bob]

2 hours ago, Rob-M said:

That's what I reckon somebody needs to be doing, so between the four of you on here you need to start marketing a drop in solution.

The problem would be to give a warranty with the system. 3 of us have bought 2nd hand batteries from Jeremy ....and while they look good, can they really be relied upon? I know mine were tested to check they could deliver the full 'advertised current (0.5C ????) for a specified duration and passed....but does that help estimate how long they will last? It is a risk but the boat duty is so so lighter than a car....so they should last.

We all have slightly different systems which have been tailored to our own set up.

MP's is fully automatic and disconnects on full charge based on amps in - based on his home brew management system. My system disconnects on voltage (simple from a BMV) and to be idiot proof needs a bit more work to map out solar charging voltages...but is good if you are not an idiot. Peter's is very simple as he is not using an alternator and just relies on voltage.

The fact I got mine to work shows how easy it is to do yourself with just a basic electrickerty skill and the ability to learn how to crimp 50mm cables.

I think it needs to be more like a self help group where all the info how the different ways to do it are easily available and 'mentors' are available to advise how to tailor it to your circumstances.

[peterboat]

I agree with all the comments above, My friend James who I bought my batteries from is going into production of aluminium skiffs for the Thames, he is making outboards for them and supplying good second hand batteries. I only thought he would be better with direct drive through the keel, as its simpler, and allows a wheel if wanted.

I am more than happy to help anyone with my electric drive and my solar/whispergen only domestic setup.

[Tony Brooks]

22 hours ago, Dr Bob said:

I think it needs to be more like a self help group where all the info how the different ways to do it are easily available and 'mentors' are available to advise how to tailor it to your circumstances.

 

We have that on here but the technical bits on how each of you have done it are spread across threads and buried inside topics so I suspect the ideal solution would be for a mod to set up a new "closed" forum and invite specific individuals to post "how I did it" pieces. Maybe a sub-forum on "how I am getting on with it" and perhaps another "problems I found".

 

That way the rest of us could not muddy the topic s with a load of questions but could post questions on (say) the maintenance forum.

 

I would much rather trust a UK forum with contributions from people with a proven track record across technical subjects than something from the USA.

[Dr Bob]

36 minutes ago, Tony Brooks said:

 

and perhaps another "problems I found".

 

No, we dont need that bit.

[Dr Bob]

41 minutes ago, Tony Brooks said:

 

We have that on here but the technical bits on how each of you have done it are spread across threads and buried inside topics so I suspect the ideal solution would be for a mod to set up a new "closed" forum and invite specific individuals to post "how I did it" pieces. Maybe a sub-forum on "how I am getting on with it" and perhaps another "problems I found".

 

That way the rest of us could not muddy the topic s with a load of questions but could post questions on (say) the maintenance forum.

 

I would much rather trust a UK forum with contributions from people with a proven track record across technical subjects than something from the USA.

I think something like that could work and despite my previous post there ARE a number of things that do need working out for DIY systems. Whilst the 'sub' forum needs to have good contributions from those with the experience, we do need input from others who can help sort the issues that are present.

I see at least two areas where some deeper discussion is needed.

i) auto disconnect relays. I am using a BEP motorised switch to disconnect. Works great from the voltage relay on the BMV but is £150. Tom uses the same. MP uses a much cheaper 'automotive' relay (£60 ....or maybe £25 from a scrap yard), but it is a latching relay and how do you activate that from a BMV? There is one commercial unit to do it for £80! MP built his own, integrated into his management system. Building a circuit to do it is maybe beyond me ...but not to experts like MP or NN. I wonder if there are cheap solutions on fleabay? More discussion needed.

ii) Peter's system is nice and simple but he doesnt use an alternator. What is the best way to integrate an alternator and how hard can they be run? They can be turned off by the auto disconnect but it would be better if the big power relay doesnt have to switch every day. Mine has only switched off twice in 4 months ....and then I was forcing it to test it. More important however is over driving your alternator. As per the previous thread, can our bog standard alternators withstand 60% load for 5 hours? Are there better alternators out there? Will they fit my  engine? How best to control them?

The current forum threads dont seem to get to that level of detail and the peeps who know the answers may not be reading the lithium threads.

[Iain_S]

On 14/06/2019 at 10:48, WotEver said:

Plenty of evidence to the contrary, Bob. Here’s the first one I found, loads more if you keep looking:

http://liionbms.com/php/wp_cccv_charging.php

Not sure I follow how the mismatch is corrected by charge/discharge cycles, given the low self discharge of LiFePO₄ and that the cells are in series, so current through them must be identical.

 

e.t.a.  ... unless passive balancing is added.

Edited June 16, 2019 by Iain_S

[Dr Bob]

On 14/06/2019 at 10:48, WotEver said:

Plenty of evidence to the contrary, Bob. Here’s the first one I found, loads more if you keep looking:

http://liionbms.com/php/wp_cccv_charging.php

I think Mike has answered this already but worth saying that I do keep a daily look at the cell voltages and will glance at them once the voltage gets to 13.5V with the alternator on. Typically then they are at 3.38V +\- 0.025V. The key then is the delta between the highest and lowest which which is typically 50-70mV on a charge of 30-40A. Its been the same since I started. BUT, this is all at less than 80% SoC. It may not be same above it.

You are right that if that delta was to get much bigger, then one of the cell voltages could get much higher, but I do have an auto disconnect circuit if any cell gets to 3.80V. I think MP has a trip on his system if the delta increases too much but his trip cuts out on tail current so catches the solar issue.

What I dont know...and no one has been able to answer is if you charge your bank up to 13.9V and start seeing the knee and see the tail current drop off (happens in the last 3% of charge) then stop charging, then apply a voltage of 13.2V from a solar mppt, will there be a flow of amps into the bank? Lets assume the mppt has gone into float. Dont forget the rested voltage at 100% SoC is around 13.4V ish. I assume no amps will flow into the batteries?

The other case is that you charge your bank to 90% SoC via the alternator so say 45Ahrs short of full and then stop charging with the engine. The solar then takes over. If the charge is 20A then the voltage will rise such that the auto disconnect will trip mine at the voltage limit or the current reduction in the knee will trip MPs. If however it is 10A, I am not sure how fast the voltage rises and will it trip the disconnect? It would take 4 hours to get to that point. There then could be an issue if the cells were out of balance. They are not out of balance in my normal operating range but will the delta be too high when I next get them up to near 100% (its been 7 weeks since I was there last).

In practice, I am never seeing this case as I never let them go over 80% so not seeing anywhere near 100%.

MP is taking his up to 100% almost everyday due to his current heavy boating schedule, but his disconnects anyway when full so solar not an issue.

 

For info, I managed to get them up to 80% SoC today but its sun and showers this afternoon, and with the telly on, my 500W of solar is never going to get near 85%. I will try later in the week to see if I can check the balance at higher SoC's but everything is pretty normal today.

 

[cuthound]

7 hours ago, Dr Bob said:

No, we dont need that bit.

 

It would be more helpful if it had solutions to the problems found. 

[MtB]

 

Never mind the details for now, are we agreed a board specifically for home-brew lithium battery installations would be a Good Idea?

 

 

[peterboat]

So I have been away from the boat all week, solar was left turned on, screen shows no amps going into the batteries, they are reading 13.4 volts and thats it! I have switched on the inverter kettle is boiled and the amps are going back in, its sunny here so a lot of amps are going in! My solar immersion has heated the water so all is well in my world, clearly their are MPPT solar controllers that are designed for the job and some that arnt, sometimes spending the money on a midnite controller with LifePo4s is money well spent

[MtB]

2 minutes ago, peterboat said:

 sometimes spending the money on a midnite controller with LifePo4s is money well spent

 

Pete, What does the Midnight controller do that a Tracer doesn't??

 

[peterboat]

1 hour ago, Mike the Boilerman said:

 

Pete, What does the Midnight controller do that a Tracer doesn't??

 

Work!! A while a go before the Midnite I had 2 Tracers they always worked against each other, so I invested in the Midnite, My mate bought them from me he managed to knacker both of them!! He too as a midnite one now and as yet it has survived

[MtB]

4 minutes ago, peterboat said:

Work!! A while a go before the Midnite I had 2 Tracers they always worked against each other, so I invested in the Midnite, My mate bought them from me he managed to knacker both of them!! He too as a midnite one now and as yet it has survived

 

 

Lol my Tracer works just fine. I must be doing it wrong!!!!

 

 

[Dr Bob]

2 hours ago, peterboat said:

So I have been away from the boat all week, solar was left turned on, screen shows no amps going into the batteries, they are reading 13.4 volts and thats it! I have switched on the inverter kettle is boiled and the amps are going back in, its sunny here so a lot of amps are going in! My solar immersion has heated the water so all is well in my world, clearly their are MPPT solar controllers that are designed for the job and some that arnt, sometimes spending the money on a midnite controller with LifePo4s is money well spent

Very interesting. 13.4V and no amps going in.

That must mean they are at 100%. If they were less, then they would not be at 13.4V yet no current is flowing so no overcharging.

Any idea of cell voltages Peter? Not sure if you have them.

I will try and force mine up to 100% and get the solar charging....but its all gloomy her again and we are under trees!

[BruceinSanity]

31 minutes ago, Dr Bob said:

we are under trees!

Hmmm... is that better or worse than being under the doctor? 

[peterboat]

55 minutes ago, Dr Bob said:

Very interesting. 13.4V and no amps going in.

That must mean they are at 100%. If they were less, then they would not be at 13.4V yet no current is flowing so no overcharging.

Any idea of cell voltages Peter? Not sure if you have them.

I will try and force mine up to 100% and get the solar charging....but its all gloomy her again and we are under trees!

Sorry Bob have been using them for cups of coffee and tinternet etc, should have done it straight away

[Dr Bob]

48 minutes ago, peterboat said:

Sorry Bob have been using them for cups of coffee and tinternet etc, should have done it straight away

Not to worry.

[cuthound]

6 hours ago, Dr Bob said:

Very interesting. 13.4V and no amps going in.

That must mean they are at 100%. If they were less, then they would not be at 13.4V yet no current is flowing so no overcharging.

Any idea of cell voltages Peter? Not sure if you have them.

I will try and force mine up to 100% and get the solar charging....but its all gloomy her again and we are under trees!

 

I reckon the current prolonged spell of rain is caused by all you lot with solar sucking all the rays out of the sun.

 

After all it can't be MrSmelly's fault this time as he's back on his mooring. ?