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Cheap LiFePO4 BMS?


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13 minutes ago, nicknorman said:

 I can see the cost of the new Chinese cells but have no idea what people have paid for Jeremy’s second hand cells.

I paid £1000 for 480hrs at 12V ie 12 cells.

MP got his 10% cheaper!

I asked Peter a while back about his cells and I think his mate was selling them at about £400 for 160Ahr at 12V - so they have gone up a bit.

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1 hour ago, Dr Bob said:

I paid £1000 for 480hrs at 12V ie 12 cells.

MP got his 10% cheaper!

I asked Peter a while back about his cells and I think his mate was selling them at about £400 for 160Ahr at 12V - so they have gone up a bit.

£375 each at the moment but they do have a BMS to stop all the ups and downs in life, I am just trying to buy a BMS for my small electric car its 15s 400amps at 60 volts so lets see what I get quoted. If I just wanted a balance while charging and passive BMS rated at 60 amps I could get one for 70 squids, and that might be the way I go if the price is way to expensive

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On 06/07/2020 at 12:51, WotEver said:

I've flown inverted a few times.  It's quite disconcerting as one's frame of reference is the aircraft in which you're sat, so the first time it happened I was wondering why my arms suddenly wanted to fly above my head. I was more concerned about that than why the ground and sky had swapped places.

I seem to recall all the dirt and dust from the floor of a Blanik falling like a shower of ..... dirt and dust ......

Edited by LadyG
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3 hours ago, Dr Bob said:

I paid £1000 for 480hrs at 12V ie 12 cells.

MP got his 10% cheaper!

I asked Peter a while back about his cells and I think his mate was selling them at about £400 for 160Ahr at 12V - so they have gone up a bit.

So not that much cheaper than new from China, which would be about £1400 for similar.

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21 minutes ago, nicknorman said:

So not that much cheaper than new from China, which would be about £1400 for similar.

Would seem so, however I bought 30 x 36 volt LifePo4s, some were well charged others were showing 2.7 volts I put these into batches of 10 and charged them, all but 3 went to flashing green BMS, they hold a charge and push the boat along very well. Its a 72 volt bank interconnect and clearly stays well balanced, this is all because they have a good BMS. The 3 bad batteries I dismantled and checked cells, quite a few were knackered, even ones that tested ok when made into a 12 volt bank performed poorly and some burst even with moderate charging. I had charged the cells separately first but under usage they soon lost balance. 

4 valence battery with low cycles in reality are a bargain at 375 squids each,  as the BMS does work and they are quality batteries 

Edited by peterboat
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2 hours ago, peterboat said:

£375 each at the moment but they do have a BMS to stop all the ups and downs in life, I am just trying to buy a BMS for my small electric car its 15s 400amps at 60 volts so lets see what I get quoted. If I just wanted a balance while charging and passive BMS rated at 60 amps I could get one for 70 squids, and that might be the way I go if the price is way to expensive

Ah!

Why not just get a Tesla. They dont half go fast! Best car I have ever driven.

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59 minutes ago, nicknorman said:

So not that much cheaper than new from China, which would be about £1400 for similar.

There is a lot of bumph on the 'Marine how to' site about low quality chinese cells but a lot of it is aimed at the BMS systems they put in them. What is for certain is that the Winston Thundersky cells are good quality. Until there are lots of adopters, I guess we wont really know how good these cheaper cells are. The Li threads on the cruiser forum are now getting on for 10 years old and there is always some good info to be had from them.

It's an interesting question - if my Li's gave up, what would I get to replace them? I really dont know the answer to that. Peter's solution looks good but I am impressed with the Thundersky's....but what else is out there?

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3 minutes ago, Dr Bob said:

Ah!

Why not just get a Tesla. They dont half go fast! Best car I have ever driven.

I only like the model S!

I am playing at the moment Andy, I have 2 Aixam electric cars both are sepex motors running at 48v nominal, I am building a bank of 17.6 KWHs which is 15p x 15s its just a small city car so should have a good range. I am looking at getting it to do 55mph rather than the 40 mph its designed to do, I have a AC drive train as well so we will see what I end up with ?

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4 hours ago, nicknorman said:

This brings up a point that I don’t think has really been discussed. Which source of LiFePO4 cells (without BMS) for a boater? By which I think I mean Jeremy (as per quite a few on here) or new, direct from China (as per Dre). I can see the cost of the new Chinese cells but have no idea what people have paid for Jeremy’s second hand cells.

I'm not sure if I should broadcast how much I paid (in case it affects Jeremy's business - awfully nice chap), but I sent you a PM Nick and I'd be happy to let anyone else know privately, just send me a message.

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16 minutes ago, ivan&alice said:

I'm not sure if I should broadcast how much I paid (in case it affects Jeremy's business - awfully nice chap), but I sent you a PM Nick and I'd be happy to let anyone else know privately, just send me a message.

Got it, thanks.

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6 hours ago, nicknorman said:

This brings up a point that I don’t think has really been discussed. Which source of LiFePO4 cells (without BMS) for a boater? By which I think I mean Jeremy (as per quite a few on here) or new, direct from China (as per Dre). I can see the cost of the new Chinese cells but have no idea what people have paid for Jeremy’s second hand cells.

If I hadn't bought second hand Valence, I would probably have bought from here:

 

https://shop.gwl.eu/

 

I would have bought from Jeremy, but he was far to busy to sort anything out for me.

 

 

 

Edited by Richard10002
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I paid £1200 for 4 x 130Ah 12V Valence Li Batteries second hand in November.

 

I think it is fair to say that the "BMS" in each of the Valence batteries will allow you to monitor the battery via a PC with the Valence Software, but it does nothing to protect against over and under voltage, or temperature. Apparently there is a gizmo you can buy that will monitor and protect a bank, but they are either very expensive, or not available.... I have found nobody who has one.

 

I have a Victron BMV 712 monitor, so can keep a close eye on them on my phone - it also has alarms for low and high voltage. I do have a Victron low voltage cutoff gizmo. I keep a close eye on them when charging and have had no difficulty keeping them from reaching too high a voltage. When I get around to it, I'll fit a relay in the charging cable, which activates via the BMV alarm - I might be able to make this react to both temperature and voltage, although I'm not sure temperature will be an issue, (high or low), in side the living area on a canal in Manchester.

 

When I say "a close eye when charging"..... charging with the genny at 60A, it takes a bit over 6 hours to put 360Ah in, so I only need to be watching closely for the last half hour or so when the sun isn't shining. A bit more often when it is.

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6 minutes ago, Richard10002 said:

I paid £1200 for 4 x 130Ah 12V Valence Li Batteries second hand in November.

 

I think it is fair to say that the "BMS" in each of the Valence batteries will allow you to monitor the battery via a PC with the Valence Software, but it does nothing to protect against over and under voltage, or temperature. Apparently there is a gizmo you can buy that will monitor and protect a bank, but they are either very expensive, or not available.... I have found nobody who has one.

 

I have a Victron BMV 712 monitor, so can keep a close eye on them on my phone - it also has alarms for low and high voltage. I do have a Victron low voltage cutoff gizmo. I keep a close eye on them when charging and have had no difficulty keeping them from reaching too high a voltage. When I get around to it, I'll fit a relay in the charging cable, which activates via the BMV alarm - I might be able to make this react to both temperature and voltage, although I'm not sure temperature will be an issue, (high or low), in side the living area on a canal in Manchester.

 

When I say "a close eye when charging"..... charging with the genny at 60A, it takes a bit over 6 hours to put 360Ah in, so I only need to be watching closely for the last half hour or so when the sun isn't shining. A bit more often when it is.

Richard I can assure you that the BMS does work James charged a flat valence up green light came on and battery was in balance when he plugged in. Same with my 36 volts jobbies  all cells balanced when charged from 2.7 volts using solar, none of this is would happen without a BMS working. 

Have you had to balance your batteries at all since November?

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On 08/07/2020 at 22:18, nicknorman said:

Yes if you want 10A from 3.3v you need 0.33 ohms. And the power dissipation will be v x I, ie 33 watts.
Of course you probably want it to work at max charging voltage ie 3.7 volts so 0.33 ohms would give you about 11A and 41w

 

something like this would do https://uk.rs-online.com/web/p/panel-mount-fixed-resistors/0160887/

but note that the 50w rating is only when the resistor is mounted on a large heatsink using thermal paste to make a good thermal connection. And at maximum power dissipation even with a heatsink it can reach 200C which is definitely ouch territory!

Excuse the ignorant question, but this resistor doesn't specify a voltage rating - but I assume this will work at 3.2V (or 3.7V) right? What makes a component suited to a particular voltage? Switches/relays I can understand, because if the break is not appropriate I can imagine the current arcing or the contacts fusing. But can any resistor be used at any voltage?

I have a 600W 12V heating element (for my calorifier) - this is basically a resistor right? Why is this a "12V" resistor and not a 24 or 48V resistor? 

You guys were alluding to Ohm's law, so I did some calculatiosn - 600W at 12V implies 0.24Ω (Ohm's law) and 50A current for my calorifier heating element. 

So if I plug 3.7V and 0.24Ω into Ohm's law I get 15A current, 57W power. This sounds about ideal to take some power out of my cell 3. 

 

Does it work like that? Is there any harm in giving it a go?

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16 minutes ago, ivan&alice said:

Excuse the ignorant question, but this resistor doesn't specify a voltage rating - but I assume this will work at 3.2V (or 3.7V) right? What makes a component suited to a particular voltage? Switches/relays I can understand, because if the break is not appropriate I can imagine the current arcing or the contacts fusing. But can any resistor be used at any voltage?

I have a 600W 12V heating element (for my calorifier) - this is basically a resistor right? Why is this a "12V" resistor and not a 24 or 48V resistor? 

You guys were alluding to Ohm's law, so I did some calculatiosn - 600W at 12V implies 0.24Ω (Ohm's law) and 50A current for my calorifier heating element. 

So if I plug 3.7V and 0.24Ω into Ohm's law I get 15A current, 57W power. This sounds about ideal to take some power out of my cell 3. 

 

Does it work like that? Is there any harm in giving it a go?

I did say it's what I would do, I have a 3kw 220 volt Ac immersion working from whatever the solar puts in at dc! If its sunny, water very hot if it isnt water warm it works mate and has for a couple of years

Edited by peterboat
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5 minutes ago, ivan&alice said:

Excuse the ignorant question, but this resistor doesn't specify a voltage rating - but I assume this will work at 3.2V (or 3.7V) right? What makes a component suited to a particular voltage? Switches/relays I can understand, because if the break is not appropriate I can imagine the current arcing or the contacts fusing. But can any resistor be used at any voltage?

Yes, for all voltages you'll find in a boat. There are limitation in the kilovolt range.

5 minutes ago, ivan&alice said:

I have a 600W 12V heating element (for my calorifier) - this is basically a resistor right? Why is this a "12V" resistor and not a 24 or 48V resistor? 

It's a twelve volt heating element because it has the correct resistance to dissipate 600W when fed from 12V. A 24V 600W heating element would have four times greater resistance.

5 minutes ago, ivan&alice said:

You guys were alluding to Ohm's law, so I did some calculatiosn - 600W at 12V implies 0.24Ω (Ohm's law) and 50A current for my calorifier heating element. 

So if I plug 3.7V and 0.24Ω into Ohm's law I get 15A current, 57W power. This sounds about ideal to take some power out of my cell 3. 

 

Does it work like that? Is there any harm in giving it a go?

Yes, it does work like that, and yes, that would be idea.

 

MP.

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1 minute ago, peterboat said:

I did say it's what I would do, I have a 3kw 120 volt Ac emmersion working from whatever the solar puts in ! If its sunny water very hot if it isnt water warm it works mate and has for a couple of years

I meant to drain the charge out of my unbalanced high voltage cell, not to actually heat the hot water (however that is the ultimate reason I have the element - I eventually want to shed excess power into my calorifier at some point).

Just now, MoominPapa said:

Yes, for all voltages you'll find in a boat. There are limitation in the kilovolt range.

It's a twelve volt heating element because it has the correct resistance to dissipate 600W when fed from 12V. A 24V 600W heating element would have four times greater resistance.

Yes, it does work like that, and yes, that would be idea.

 

MP.

Thanks MP! I will let you guys know how it goes. 

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2 minutes ago, ivan&alice said:

I meant to drain the charge out of my unbalanced high voltage cell, not to actually heat the hot water (however that is the ultimate reason I have the element - I eventually want to shed excess power into my calorifier at some point).

Seems like a win-win.

 

Balance the Lithium and warm the water (slightly)

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Going OK so far - 11A coming in from my solar. 

Cell 1: 3.362V
Cell 2: 3.384V
Cell 3: 3.403V (with the 15A load on it)
Cell 4: 3.370V

Water is verrrry mildly warm. Going to see how it goes and try to get all my cells up to 3.6V nice and balanced.

Thanks for all the advice, appreciate having some handholding through this. 

 

 

 

EDIT: 

Still going 45 mins later, sun has come out a bit and producing 19A of current.

 

Cell 1: 3.372V

Cell 2: 3.407V

Cell 3: 3.540V

Cell 4: 3.387V

 

Water is warm. Checking the voltage every minute or two. If Cell 3 gets to 3.6V I'll pull the plug.

Edited by ivan&alice
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1 hour ago, ivan&alice said:

Going OK so far - 11A coming in from my solar. 

Cell 1: 3.362V
Cell 2: 3.384V
Cell 3: 3.403V (with the 15A load on it)
Cell 4: 3.370V

Water is verrrry mildly warm. Going to see how it goes and try to get all my cells up to 3.6V nice and balanced.

Thanks for all the advice, appreciate having some handholding through this. 

 

 

 

EDIT: 

Still going 45 mins later, sun has come out a bit and producing 19A of current.

 

Cell 1: 3.372V

Cell 2: 3.407V

Cell 3: 3.540V

Cell 4: 3.387V

 

Water is warm. Checking the voltage every minute or two. If Cell 3 gets to 3.6V I'll pull the plug.

The water on my boat is very hot cos sun is hot 

Glad it's worked out ok, I did say to use immersion but when others said not I thought they knew something I didn't 

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6 hours ago, ivan&alice said:



You guys were alluding to Ohm's law, so I did some calculatiosn - 600W at 12V implies 0.24Ω (Ohm's law) and 50A current for my calorifier heating element. 

So if I plug 3.7V and 0.24Ω into Ohm's law I get 15A current, 57W power. This sounds about ideal to take some power out of my cell 3. 

 

Does it work like that? Is there any harm in giving it a go?

Agggghr!!!!!

I spent hours trying to find resistors that were cheap and gave the right resistance to make a 10-20A depletion circuit.

I could have used an immersion element. Well done identifying a simple way of doing it. Interesting to see how many Ahrs you need to take out.

Well done.

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11 minutes ago, Dr Bob said:

Agggghr!!!!!

I spent hours trying to find resistors that were cheap and gave the right resistance to make a 10-20A depletion circuit.

I could have used an immersion element. Well done identifying a simple way of doing it. Interesting to see how many Ahrs you need to take out.

Well done.

Bob its called KISS when you said no I thought you knew something I didnt

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19 hours ago, peterboat said:

Richard I can assure you that the BMS does work James charged a flat valence up green light came on and battery was in balance when he plugged in. Same with my 36 volts jobbies  all cells balanced when charged from 2.7 volts using solar, none of this is would happen without a BMS working. 

Have you had to balance your batteries at all since November?

as it happens, there is one cell in one of the batteries which causes an imbalance of about 250mv when getting close to 3.65V. The "balancing" function seems somewjat halfhearted, and would take forever to balance it, so I haven't bothered. If I stay below about 90% SOC, the imbalance is less than 100mV. I suppose if I was on shorepower, I could leave it charging at 14V or so, and see how the balancing worked out - but I'm not.

 

Anyway... in the post you referred to i stated that it does nothing to protect against high/low voltage or temperature, which is a big part of the job of a BMS, or that's what I thought. I think that's why you charge to about 13.9V, and no more, isn't it?

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2 minutes ago, Richard10002 said:

as it happens, there is one cell in one of the batteries which causes an imbalance of about 250mv when getting close to 3.65V. The "balancing" function seems somewjat halfhearted, and would take forever to balance it, so I haven't bothered. If I stay below about 90% SOC, the imbalance is less than 100mV. I suppose if I was on shorepower, I could leave it charging at 14V or so, and see how the balancing worked out - but I'm not.

 

Anyway... in the post you referred to i stated that it does nothing to protect against high/low voltage or temperature, which is a big part of the job of a BMS, or that's what I thought. I think that's why you charge to about 13.9V, and no more, isn't it?

I change to 13.9 to give me batteries for my lifetime, 100% does them no favours and if it good enough for Tesla its good enough for me. I have always said that 80% is the right figure and stick to it, I am looking at a BMs for my car, that it seems only makes minor adjustment on the cells but has the ability to stop and start charging but don't think it cuts output just reduces it. For our uses these batteries work well and will last us two out for sure 

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