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Cheap LiFePO4 BMS?

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2 minutes ago, WotEver said:

I doubt it would be cheaper to have 260A Mosfets as opposed to a relay. And I know which one I’d trust more in a fault condition. 

 

1) Woss a Mosfet?

 

2) Which would you trust more in a fault condition, and why?

 

 

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Just now, Mike the Boilerman said:

1) Woss a Mosfet?

Kinda like a solid state switch. Think of it as a transistor on steroids. 
 

1 minute ago, Mike the Boilerman said:

2) Which would you trust more in a fault condition, and why?

Relay, because it is much less likely to give up its magic smoke and fail either open or closed (or halfway). 

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9 hours ago, Mike the Boilerman said:

 

Given Peter always seems to focus on cell balance when discussing BMSs and his are always balanced, yet users of bare cells report they drift, I'm wondering if the 'BMS' built into each of Peter's batteries is actually a cell balancing device. E.g. something like this device mentioned by Tom and Bex:

 

https://www.ebay.co.uk/itm/254003975899?ul_noapp=true

 

s-l1600.jpg

 

Once the cells can be relied upon always to be balanced, then whole bank voltage becomes the only parameter that needs monitoring for disconnection if necessary. And this can be done with the Victron BMV-702 which most peeps will already have, Moomin's planned latching relay drive module and a latching relay. Either the £10 120A relay from GWL or the £60 190A relay from RS.

 

 

 

 

 

Your point about the BMV 702 is spot on. I think it is a requirement that peeps have a battery monitor already and use it to look at V,A and Ahr on their LAs otherwise they may not be up to speed to set charging voltages correctly and understand the 'rules' for Li's. I keep banging on about just using voltage to assess SoC etc but that is because I have understood the V vs A vs Ahr relationship for my system. You can only really find the 100% full point by looking at voltage AND tail current. Voltage for termination is totally differnt when charging at 30A compared to 60A.

 

On cell balancing, I don't think it is that straight forward. Mine were balanced at the start. After the first 12 weeks off line there was a 190mV delta between top and bottom cell as I took them to 99%. I spent a few days faffing to balance them. This last week I have been up to 100% again and the delta was 70mV so I am happy so no re balancing this time. I guess in 3 more months they may have drifted out again so I have just bought the balancing box that Tom is using to try it out. Balancing is perhaps the only thing I am concerned about (long term.....as it's not a day to day problem) along with cooling for my alternator.

Edited by Dr Bob
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8 minutes ago, Dr Bob said:

Balancing is perhaps the only thing I am concerned about (long term.....as it's not a day to day problem) along with cooling for my alternator.

 

Which highlights the next issue. 

 

Initially I intend charging my lithiums using the Whispergen and solar only, as both are manually configurable to suitable voltages. The alternator typically is not. Your solution is your Sterling A to B (IIRC), mine is to just isolate the lithium bank from the LAs when I run the engine.

 

Neither of the above is really satisfactory as a basic solution for yer average boater interested in being an early adopter of lithiums, so what IS the current thinking on how use a 14.4v alternator to charge Li batts on a day-to-day basis? Use a relay to disconnect the Li bank at a given voltage and rely on an LA batt in parallel to protect the alternator? Buy a Sterling A to B? Learn how to program a RasPi? Or something else?

 

 

 

 

 

 

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21 minutes ago, WotEver said:

Kinda like a solid state switch. Think of it as a transistor on steroids. 
 

Relay, because it is much less likely to give up its magic smoke and fail either open or closed (or halfway). 

I had the magic smoke when the mosfets failed on my curtis speed controller, easily and cheaply replaced though, and the use of them is why we have PWM speed control rather than resistive speed control which wastes loads of energy

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4 minutes ago, Mike the Boilerman said:

 

Which highlights the next issue. 

 

Initially I intend charging my lithiums using the Whispergen and solar only, as both are manually configurable to suitable voltages. The alternator typically is not. Your solution is your Sterling A to B (IIRC), mine is to just isolate the lithium bank from the LAs when I run the engine.

 

Neither of the above is really satisfactory as a basic solution for yer average boater interested in being an early adopter of lithiums, so what IS the current thinking on how use a 14.4v alternator to charge Li batts on a day-to-day basis? Use a relay to disconnect the Li bank at a given voltage and rely on an LA batt in parallel to protect the alternator? Buy a Sterling A to B? Learn how to program a RasPi? Or something else?

 

 

 

 

 

 

Why not have your alternator regulator built to the correct voltage? John who bought 4 of my batteries has one thaat goes to 13.8 then drops to 13.2 volts which is ideal

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13 minutes ago, peterboat said:

Why not have your alternator regulator built to the correct voltage? John who bought 4 of my batteries has one thaat goes to 13.8 then drops to 13.2 volts which is ideal

 

It's not for just me, I/we are working out general solutions suitable for 'most boaters'. 

 

In my case I have a Leece neville 24v alternator in one boat, a 12v Lucas A127 clone on another, and a 12v Paris Rhone (I think) on the third. I wouldn't have the first clue how to rebuild the regulators on any of them.

 

Who rebuilt the regulator on John's boat?

 

An alternator regulator that drops back to a lower float voltage is most unusual I suspect, and a very custom product but yes it would be a good solution if commercially available.

 

 

Edited by Mike the Boilerman

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6 minutes ago, Mike the Boilerman said:

 

It's not for just me, I/we are working out general solutions suitable for 'most boaters'. 

 

In my case I have a Leece neville 24v alternator in one boat, a 12v Lucas A127 clone on another, and a 12v Paris Rhone (I think) on the third. I wouldn't have the first clue how to rebuild the regulators on any of them.

 

Who rebuilt the regulator on John's boat?

 

An alternator regulator that drops back to a lower float voltage is most unusual I suspect, and a very custom product but yes it would be a good solution if commercially available.

 

 

Maes which is a local vehicle electricians big concern, one of the mobile guys is a friend of mine so he did it for us, but most alternators drop to float after bulk charging older ones anyway, modern ones are controlled by the ECU

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2 minutes ago, peterboat said:

Maes which is a local vehicle electricians big concern, one of the mobile guys is a friend of mine so he did it for us, but most alternators drop to float after bulk charging older ones anyway, modern ones are controlled by the ECU

 

Ok thanks. So I wonder what he did. Maybe @Sir Nibble might care to comment?

 

The point is, to gain an understanding how to do a lithium installation oneself rather than relying on 'friends of friends' to work some voodoo magic.

 

If one of the mobile guys at Maes can do it, then probably it's not that complicated and DIY is feasible too. If DIYing the regulator to max out at 13.8v isn't practical and experts are needed, then it isn't really a viable solution to suggest to new, would-be lithium users. 

 

And do basic alternators really drop back to a float voltage? I've never noticed this happen on any of mine!

 

 

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3 minutes ago, Mike the Boilerman said:

 

Ok thanks. So I wonder what he did. Maybe @Sir Nibble might care to comment?

 

The point is, to gain an understanding how to do a lithium installation oneself rather than relying on 'friends of friends' to work some voodoo magic.

 

If one of the mobile guys at Maes can do it, then probably it's not that complicated and DIY is feasible too. If DIYing the regulator to max out at 13.8v isn't practical and experts are needed, then it isn't really a viable solution to suggest to new, would-be lithium users. 

 

And do basic alternators really drop back to a float voltage? I've never noticed this happen on any of mine!

 

 

They should otherwise the batteries will end up cooked!! or is that boiled? thats what the regulator pack  is for to regulate

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10 minutes ago, Mike the Boilerman said:

 

I agree they should, but my question is do they?!

No they don’t. 

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22 minutes ago, Mike the Boilerman said:

 

Ok thanks. So I wonder what he did. Maybe @Sir Nibble might care to comment?

 

The point is, to gain an understanding how to do a lithium installation oneself rather than relying on 'friends of friends' to work some voodoo magic.

 

If one of the mobile guys at Maes can do it, then probably it's not that complicated and DIY is feasible too. If DIYing the regulator to max out at 13.8v isn't practical and experts are needed, then it isn't really a viable solution to suggest to new, would-be lithium users. 

 

And do basic alternators really drop back to a float voltage? I've never noticed this happen on any of mine!

 

 

Nor have I. Tens of thousands of them with one setting only. I have started varying output voltage of some ECU controlled units with a cheapo pwm generator from eBay, just mucking around.

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1 minute ago, WotEver said:

No they don’t. 

 

Fanx.

 

And after some goggling, I'm finding it surprisingly difficult to find out how an alternator regulator is designed. Found one circuit diagram and it looks to me as though individual resistor values would need to be changed, and to what? And getting at them near impossible as I'd guess the innards of a regulator are likely to be potted in resin or similar. 

 

 

overcharging-alternator-73-cj5.jpg?w=800

 

 

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15 hours ago, Mike the Boilerman said:

 

 

 

But there is more. I see ev-power.eu have a latching 120A relay for only 11 Euros. Here:

https://www.ev-power.eu/Battery-Management/DC-Power-Latching-Relay-100A-Coil-12V.html?cur=1

dsc_0690_z1.jpg

So I have just ordered the GWL cell performance monitor board above and three of these latching relays. Total cost including shipping and the 4% PayPal surcharge came almost exactly £200 all in.

 

 

 

 

 

 

But you have a 24v system - you appear to have ordered 3 off 12 volt relays.

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7 minutes ago, Alan de Enfield said:

 

But you have a 24v system - you appear to have ordered 3 off 12 volt relays.

 

Yes. I have 12v available too. 24v latching relays for a tenner each are rarer than hens teeth.

 

 

 

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1 hour ago, Mike the Boilerman said:

 

Which highlights the next issue. 

 

Initially I intend charging my lithiums using the Whispergen and solar only, as both are manually configurable to suitable voltages. The alternator typically is not. Your solution is your Sterling A to B (IIRC), mine is to just isolate the lithium bank from the LAs when I run the engine.

 

Neither of the above is really satisfactory as a basic solution for yer average boater interested in being an early adopter of lithiums, so what IS the current thinking on how use a 14.4v alternator to charge Li batts on a day-to-day basis? Use a relay to disconnect the Li bank at a given voltage and rely on an LA batt in parallel to protect the alternator? Buy a Sterling A to B? Learn how to program a RasPi? Or something else?

 

Wow Mike, you are keeping up! Spot on with your questions.

I asked the same question back in January. See

 

2nd post on page 3.

 

There was quite a bit of discussion but no real answers. We really need a commercial box that an be connected between the alternator and batteries that can do the job without having to remove the alternator and get the soldering iron out.  If I had to take my alternator apart, I wouldnt have gone Lithium. I guess my Sterling AtoB does the job - something it wasnt designed to do - but could a simplified AtoB work? IIRC Tom fitted a 'development' board (page one of the above link) to control his alternator but that board is now commercial and being sold for $500 a pop.

MP took the view that using the Tyco relay to disconnect as the way to control the alternator voltage was ok as they are rated at high cycle counts. Maybe then you could have 2 tyco's. One operating to isolate the alternator and a 2nd as the emergency cut out on high cell voltage.

.......then again, shirley there must be loads of Sterling AtoB on the 2nd hand market 'cause everyone except me thinks they are cr*p!

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3 minutes ago, Dr Bob said:

Wow Mike, you are keeping up! Spot on with your questions.

I asked the same question back in January. See

 

2nd post on page 3.

 

There was quite a bit of discussion but no real answers. We really need a commercial box that an be connected between the alternator and batteries that can do the job without having to remove the alternator and get the soldering iron out.  If I had to take my alternator apart, I wouldnt have gone Lithium. I guess my Sterling AtoB does the job - something it wasnt designed to do - but could a simplified AtoB work? IIRC Tom fitted a 'development' board (page one of the above link) to control his alternator but that board is now commercial and being sold for $500 a pop.

MP took the view that using the Tyco relay to disconnect as the way to control the alternator voltage was ok as they are rated at high cycle counts. Maybe then you could have 2 tyco's. One operating to isolate the alternator and a 2nd as the emergency cut out on high cell voltage.

.......then again, shirley there must be loads of Sterling AtoB on the 2nd hand market 'cause everyone except me thinks they are cr*p!

 

And coincidentally this is about the same price as a Sterling A to B..!

 

From the Sterling site it appears the lowest voltage setting is 14.1v (for AGM). Still a bit high really isn't it? 

 

Using another Tyco seems clumsy and brutish although it will prolly work. Might be a tendency for it to cycle on and off rapidly as switching voltage is achieved if the right hysteresis is not considered carefully. 

 

Will have a read of that thread later, need to go out now and mend stuff!

 

 

 

 

 

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10 hours ago, Craig Shelley said:

Are there any solid state solutions to this available yet?

Should be a lot cheaper and simpler than latching or motorised switches, in theory.

Would still want to have a proper switch for manual isolation though.

“Drop in” batteries typically have mosfets for over and under voltage protection, but this results in limited maximum discharge rate. Fine if you just want lights, pump, fridge, but no good if you have a 3kw inverter.

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1 hour ago, Mike the Boilerman said:

... a 12v Lucas A127 clone on another...

Take a look at post #7 in this thread. I think I might have one of those regulators kicking about. Maybe that could get the charging voltage down far enough. @Sir Nibble?

 

 

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1 hour ago, Mike the Boilerman said:

From the Sterling site it appears the lowest voltage setting is 14.1v (for AGM). Still a bit high really isn't it?

 

There is a US gel setting on mine which gives the lowest voltage/current.

When on the US gel setting, the voltage rises to 13.6 - 13.7V with around 40A (reduced to 30A if the alternator is up at 95°C ish) and then goes into 'float' and the current drops to circa 5-6A and the voltage drops to 13.4-13.5V. This is around 80% SoC so even a full days boating will not take them up to 100%.

On the AGM setting, the current is 50-55A but I have not had it on this setting for more than an hour as the alternator gets up to 95°C quite quickly......to be sorted with a bilge blower (thanks Peter!)......so I have never seen the termination voltage here. I'll report back on the voltage it gets to once I sort the cooling issue....likely late november.

The 40A charging is fine for our typical boating behaviour (2-3 hours per day) outside of winter. In winter I will run the engine for an hour or two on the higher voltage setting on a mooring knowing I will never get to over 80%.

 

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2 hours ago, nicknorman said:

“Drop in” batteries typically have mosfets for over and under voltage protection, but this results in limited maximum discharge rate. Fine if you just want lights, pump, fridge, but no good if you have a 3kw inverter.

I think it still ought to be doable. MOSFETs are now down to below 500uOhms Rdson. Several in parallel would be needed for 3kw, but still cheaper than a motorised, or latching switch.

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31 minutes ago, Craig Shelley said:

I think it still ought to be doable. MOSFETs are now down to below 500uOhms Rdson. Several in parallel would be needed for 3kw, but still cheaper than a motorised, or latching switch.

Yes I’m certain it is doable, it’s just that a “drop in” battery manufacturer probably looks at a likely range of maximum currents required by customers, and pitches the design at a mid to high point, not at the max. Typically the max continuous discharge rate quoted, is far less than the actual cells could happily tolerate.


You and I are electronic types, we would be quite happy with solid state. But I think there is a contingent on here that would only be happy with something that whirred, moved, clunked and sparked!

Edited by nicknorman

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2 hours ago, nicknorman said:

 


You and I are electronic types, we would be quite happy with solid state. But I think there is a contingent on here that would only be happy with something that whirred, moved, clunked and sparked!

You in your youf Nick?

 

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7 hours ago, Mike the Boilerman said:

 

Fanx.

 

And after some goggling, I'm finding it surprisingly difficult to find out how an alternator regulator is designed. Found one circuit diagram and it looks to me as though individual resistor values would need to be changed, and to what? And getting at them near impossible as I'd guess the innards of a regulator are likely to be potted in resin or similar. 

 

 

overcharging-alternator-73-cj5.jpg?w=800

 

 

Really? I advance you this, I did try it today on a car ad it did regulate the voltage, turn lights and fan on and it upped output

How Does an Automotive Voltage Regulator Work? | It Still Runs

 

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