Cheap LiFePO4 BMS?

[Murflynn]

7 hours ago, nicknorman said:

 

 

Of course if our public transport wasn’t worse than most 3rd world countries, it would be better.

well, that is certainly a truism  ....................  sorry, couldn't resist 

[George and Dragon]

6 minutes ago, peterboat said:

I do not see the point of making electric by diesel genny except in emergency solar is best for me

A diesel-electric? Someone with a better knowledge of the railway system in this country will, I feel sure, be along to tell me why British Rail didn't electrify the network when they dispensed with steam locos.

[BEngo]

1 hour ago, George and Dragon said:

A diesel-electric? Someone with a better knowledge of the railway system in this country will, I feel sure, be along to tell me why British Rail didn't electrify the network when they dispensed with steam locos.

Cost, (principally of the overhead wires, but also of signalling for higher speeds),  unions and political short sightedness. 

 

There are lots of books which tackle the issues, and no doubt plenty of stuff on the web if you are sufficiently interested.

N

[peterboat]

1 hour ago, George and Dragon said:

A diesel-electric? Someone with a better knowledge of the railway system in this country will, I feel sure, be along to tell me why British Rail didn't electrify the network when they dispensed with steam locos.

On the broads some of the newer hire boats are hybrids with solar, the gennys are automatically started if the batteries go low, sunny days often the gennys arnt needed 

[George and Dragon]

2 hours ago, BEngo said:

Cost, (principally of the overhead wires, but also of signalling for higher speeds),  unions and political short sightedness. 

 

There are lots of books which tackle the issues, and no doubt plenty of stuff on the web if you are sufficiently interested.

N

I'll probably get my knuckles rapped for a 'political comment' but it seems to me little has changed in the intervening period.  

 

2 hours ago, peterboat said:

On the broads some of the newer hire boats are hybrids with solar, the gennys are automatically started if the batteries go low, sunny days often the gennys arnt needed 

At least the genny should be optimised for efficiency.

[peterboat]

12 hours ago, George and Dragon said:

I'll probably get my knuckles rapped for a 'political comment' but it seems to me little has changed in the intervening period.  

 

At least the genny should be optimised for efficiency.

They are, in reality they are range extenders as the electric motor is the only thing attached to the propshaft same as my boat, except I only have solar panels for charging 

[pgrange]

Good morning everyone. 

 

I have been reading this thread with interest. I have just installed my diy powerwall made from 420 recycled 18650 cells to form a 7s60p 24v 120A setup. Taking into account the cells are recycled my own tests suggest I have 100A usable. I've installed an Iconica 3KW hybrid inverter together 1000w of solar panels. I'm using a Chargery BMS to look after the Li. The BMS has a number of safety features including the ability to control a relay offering protection against over charging over discharging, high and low temp cut off all configurable. 

 

The part of the puzzle I'm having issues with is charging the batteries from the alternator. Reading here it looks like quite a conundrum. I've seen people mention the Sterling AtoB which looks like a nice piece of kit but at £350 a bit pricey for me. My beta marine runs 2 separate alternators so I'm thinking of swapping out the existing 12v for a 24v model and using a simple voltage controlled really to switch the charge on and off. Will this work? I'm not familiar with the workings of an alternator but does it require always being connected to a load? If so could I simply dump the load to a 24v La battery when the Li have hit the correct voltage? All suggestions and help truly appreciated.

 

Many thanks 

 

Peter 

[BEngo]

Alternators produce a high voltage spike if the load is disconnected.  The spike usually fries the diodes.  If you get the right alternator the field  power wire to the regulator unit is accessible and you can stop charging by disconnecting the field, without then causing a voltage spike.  The lucas A127 is a 12 V example, but I don't know of a 24 V one.

 

Some modern ECU controlled alternators can be directed via a LIN chip and Nicknormans widget does this.

 

N

 

[TheBiscuits]

11 minutes ago, pgrange said:

I'm using a Chargery BMS to look after the Li. The BMS has a number of safety features including the ability to control a relay offering protection against over charging over discharging, high and low temp cut off all configurable. 

 

Some of their kit looks very interesting, thanks for the info.

 

https://www.chargery.com/

 

The DC and AC combined charger with built in cell balancing might be of interest to some people, and their off the shelf BMS looks worth investigating.

 

[pgrange]

3 minutes ago, BEngo said:

Alternators produce a high voltage spike if the load is disconnected.  The spike usually fries the diodes.  If you get the right alternator the field  power wire to the regulator unit is accessible and you can stop charging by disconnecting the field, without then causing a voltage spike.  The lucas A127 is a 12 V example, but I don't know of a 24 V one.

 

Some modern ECU controlled alternators can be directed via a LIN chip and Nicknormans widget does this.

 

N

 

Thanks for that. A quick Google shows they do make a 24v version for about £60. So I maybe able to control the field power wire with my voltage relay. Interesting. I'm going to have a deeper look into that. ?

[pgrange]

1 minute ago, TheBiscuits said:

 

Some of their kit looks very interesting, thanks for the info.

 

https://www.chargery.com/

 

The DC and AC combined charger with built in cell balancing might be of interest to some people, and their off the shelf BMS looks worth investigating.

 

So far it seems a nice bit of kit. It incorporates a 1.2A balance circuit so it's essential the packs are balanced beforehand. I top balanced my packs before installing and the Chargery BMS keeps everything balanced nicely. In my case I only have a 45 to 75mv difference between my 7 packs. 

[Dr Bob]

Just now, pgrange said:

Thanks for that. A quick Google shows they do make a 24v version for about £60. So I maybe able to control the field power wire with my voltage relay. Interesting. I'm going to have a deeper look into that. ?

If you use a lead acid in parallel with your Li bank then if you isolate the Li's on overcharge then the LA battery should (will) absorb the voltage spike......but you are then relying on that relay and isolation switch to protect the batteries. I choose to do that only in an emergency and try and get the charge source to shut down before the isolation switch activates so the idea of controling the field power wire is a better option.

Be careful though. Overheating of the alternator is more of a problem - you dont say what alternator you have, but on my Beta 43 with a 90A domestic alternator with poor cooling, I struggled to keep the temperature below 100°C with a 50A current. In addition to an isolation switch activated on just voltage/current, think about controlling the temperature also. A bilge blower is then a good idea (very cheap).

[magnetman]

Beta marine often fit an Iskra 175a large frame unit as the auxiliary alternator. This is what I have on my Beta 90. The other one is 70a or 90a. 

 

Another one was Leece Neville /Prestolite large frame which are very good units 160a but I think they were customer specified rather than standard equipment. 

[pgrange]

For those interested in the Chargery BMS I'll give you a brief run down. I have the BMS8T.  The main unit itself incorporates a 1.2A balancing circuit, remote display /programming unit and a current shunt. 

The main unit has a separate charge and discharge circuit to trigger relays should any of the set paramaters be met. For both charge and discharge circuits parameters can be set such as over /under voltage, over /under current over /under temperature range etc. I have wired my charge /discharge circuits in series using 2 low power solid state relays which in turn trigger a 200A 24v relay. I have tested the unit to disconnect the load at certain points and it works as expected. The voltage and current it measures reflects that of my inverter and is fairly accurate give or take a few milivolts/amps. To measure the temperature the main unit has 2 temp probes that I have placed inside 2 of the packs. Again the accuracy is pretty much bang on. 

The unit costs just over £100 delivered and comes from China so expect a few issues. The soc accuracy is appalling. You set the kw/h and AH of the pack manually and unit after a number of discharge and charge cycles works out the soc and gives a rather naff graphic displaying it. However it just doesn't work and gives a false reading. I think the issue being I only charge to 4.0v per cell and discharge to 3.6v per cell. The bms looks at this range and assumes that is the full capacity of my packs even though I have programmed the kw/h and AH. It doesn't bother me too much as but I need to set the soc disconnect parameter to 0% to prevent the unit disconnecting my load. 

All in all it appears to be a solid unit for the money and the safety features work well.  Maybe future firmware updates will solve the soc issue. 

Hope that helps some people here. 

Peter 

[nicknorman]

Presumably you are using LiPo cells?

One of the issues is with the isolation relays. If you use ordinary relays, you have to choose whether to have them powered on, or powered off. Powered on means a significant permanent current drain. Powered off is worse as it means a current drain when you are running out of battery power and risks over-discharge. Hence the use of the bistable relays, but these require a pulse to activate them, not a steady state change. Does that BMS allow for a pulsed relay activation?

[pgrange]

51 minutes ago, nicknorman said:

Presumably you are using LiPo cells?

One of the issues is with the isolation relays. If you use ordinary relays, you have to choose whether to have them powered on, or powered off. Powered on means a significant permanent current drain. Powered off is worse as it means a current drain when you are running out of battery power and risks over-discharge. Hence the use of the bistable relays, but these require a pulse to activate them, not a steady state change. Does that BMS allow for a pulsed relay activation?

Hello 

No it doesn't support a pulsed trigger and your correct with both the ssr and 200a relay there is a constant current draw. I do prefer using NO relays and the small current draw I have keeping them open is not an issue for me. I haven't actually measured it but the specs would suggest a draw of around 50ma or 12w. Not an issue for my setup . I use 18650 lipo cells. 

[nicknorman]

That's a lot of batteries to wire up! But it look a neat job. I was just thinking you must have 4 in series to give around 14.5v but you would then need around 16v to charge them giving issues with having 16v on your 12v domestic system. But then I re-read it to see that you have 7 to give 24v.

So in summary, it seems LiPo is fine for 24v  but problematic for 12v due to the cell voltages.

[MoominPapa]

3 hours ago, pgrange said:

I haven't actually measured it but the specs would suggest a draw of around 50ma or 12w. Not an issue for my setup .

On a 24v system, those two are an order of magnitude out.  If it's 50mA then it's 1.2W but if it's 12W then it's 500mA. I'd guess the later: 50mA is the holding current for a typical 5-10A relay, not a 200A monster.

 

MP.

[pgrange]

1 hour ago, MoominPapa said:

On a 24v system, those two are an order of magnitude out.  If it's 50mA then it's 1.2W but if it's 12W then it's 500mA. I'd guess the later: 50mA is the holding current for a typical 5-10A relay, not a 200A monster.

 

MP.

Yes sorry 500ma is what I should have stated ?

[pgrange]

2 hours ago, nicknorman said:

That's a lot of batteries to wire up! But it look a neat job. I was just thinking you must have 4 in series to give around 14.5v but you would then need around 16v to charge them giving issues with having 16v on your 12v domestic system. But then I re-read it to see that you have 7 to give 24v.

So in summary, it seems LiPo is fine for 24v  but problematic for 12v due to the cell voltages.

Yes it took some time. Each battery was soldered to a cable bus bar and each +ve end has an individual 5A glass fuse. If I did it again I'd invest in a spot welder. That would have sped up the job tenfold. 

[pgrange]

I made 8 packs in total so I could swap one out should it need balancing or servicing 

[MoominPapa]

56 minutes ago, pgrange said:

Yes sorry 500ma is what I should have stated ?

12AH per day is 10% of our typical on board power use, I'd be looking at ways to save that if I could.

 

MP.

 

[WotEver]

8 hours ago, nicknorman said:

... Hence the use of the bistable relays, but these require a pulse to activate them, not a steady state change.

What duration does the pulse need to be? It would be a very simple circuit to generate a pulse from a voltage flop. 

[MoominPapa]

21 minutes ago, WotEver said:

What duration does the pulse need to be? It would be a very simple circuit to generate a pulse from a voltage flop. 

between 15ms and 100ms, into a 4.7 ohm coil, for the 190A unit that most people here are using.

 

MP.

 

[WotEver]

1 minute ago, MoominPapa said:

between 15ms and 100ms, into a 4.7 ohm coil, for the 190A unit that most people here are using.

 

MP.

 

So about 3A for <100ms?   
Nicked from allaboutcircuits.com is this:

 

Experiment with the value of C1 (30uF would probably be about right) and the relay shown does the switching to the bistable. I think that’d work ok, waddya reckon?