Cheap LiFePO4 BMS?

[peterboat]

My mate John hasn't done anything other than make sure that maximum charge on his alternator is 13.8 volts and has an LA battery as starter it seems to work the alternator drops into float at 13.2 volts and the starter battery must take any shocks as of yet the alternator is still ok and batteries remain balanced. I am going to fit an over voltage disconnect for the batteries sake 

[Craig Shelley]

We've faced very similar issues as the design has evolved. The boat was already fitted with a sterling alternator controller, which was not compatible with the new battery type. Luckily, this contained a PIC, so we've written new firmware for it. The batteries are switched via a BlueSea Systems remote switch, which can easily be incorporated into a battery protection scheme.

A side effect is that this leaves the alternator vulnerable to load-dump if the batteries ever become disconnected.

So we've installed a crowbar to short the alternator phases if a voltage transient is detected. There's a YouTube video demonstrating the testing of the crowbar.

Battery monitoring is via a raspberry pi.

[Rob-M]

20 hours ago, rusty69 said:

So you are only annoying the feck out of people for 4 hours at the weekend then!

No, because when MTB isn't running his engine he is ringing the fecking church bells for hours ?

[Dr Bob]

9 hours ago, Craig Shelley said:

We've faced very similar issues as the design has evolved. The boat was already fitted with a sterling alternator controller, which was not compatible with the new battery type. Luckily, this contained a PIC, so we've written new firmware for it. The batteries are switched via a BlueSea Systems remote switch, which can easily be incorporated into a battery protection scheme.

A side effect is that this leaves the alternator vulnerable to load-dump if the batteries ever become disconnected.

So we've installed a crowbar to short the alternator phases if a voltage transient is detected. There's a YouTube video demonstrating the testing of the crowbar.

Battery monitoring is via a raspberry pi.

Please care to expand?

[nicknorman]

31 minutes ago, Dr Bob said:

Please care to expand?

Crowbar in electronics usually means something that shorts out under fault conditions. Consider how to prevent reverse polarity protection on a 12v electronic gizmo. Just put a diode in series? Well ok, but that diode always drops some voltage (0.7v or so for a silicon diode) so you end up with less than 12v at the gizmo, and you waste power in that voltage drop.

 

Alternatively, put a fuse followed by a diode connected backwards between supply and ground. In normal operation that diode is reverse biased and does nothing. Reverse connect the supply and that diode conducts, shorting the supply and thus blowing the fuse.

 

In the case mentioned above, I guess it would be a zener diode rated at a higher than normal voltage (eg 16v), and maybe a small value (high power) resistor. When the alternator is unloaded, the transient power is dumped to ground via the zener and resistor whilst the regulator catches up.

[peterboat]

19 minutes ago, nicknorman said:

Crowbar in electronics usually means something that shorts out under fault conditions. Consider how to prevent reverse polarity protection on a 12v electronic gizmo. Just put a diode in series? Well ok, but that diode always drops some voltage (0.7v or so for a silicon diode) so you end up with less than 12v at the gizmo, and you waste power in that voltage drop.

 

Alternatively, put a fuse followed by a diode connected backwards between supply and ground. In normal operation that diode is reverse biased and does nothing. Reverse connect the supply and that diode conducts, shorting the supply and thus blowing the fuse.

 

In the case mentioned above, I guess it would be a zener diode rated at a higher than normal voltage (eg 16v), and maybe a small value (high power) resistor. When the alternator is unloaded, the transient power is dumped to ground via the zener and resistor whilst the regulator catches up.

Still better to have an LA in the system I suspect? Alternators dont normally like to be shorted out

[nicknorman]

10 minutes ago, peterboat said:

Still better to have an LA in the system I suspect? Alternators dont normally like to be shorted out

Although the poster said “shorting out” he may not have meant that (let’s hope he comes back to expand). When the zener diode goes into conduction at 16v, it still preserves the 16v. It just absorbs whatever current is necessary to keep the voltage at 16v, same concept as having an LA in circuit, except at a slightly higher voltage. If your system voltage never normally goes above 14.4v, you could chose a lower zener voltage around 15v (I just chose 16v because of my natural bias towards LA-thinking - wrong!).

 

Anyway I’d be very interested to hear how he developed the code for the Pic in the Sterling reg.

 

The video he mentions is here, but I don’t really understand what’s going on

 

 

 

Edited October 21, 2019 by nicknorman

[nicknorman]

22 minutes ago, peterboat said:

Still better to have an LA in the system I suspect? Alternators dont normally like to be shorted out

Actually you’ll note he says “shorting the phases out”. Ie just the windings. Although this is perhaps a bit drastic, it shouldn’t damage the alternator windings - it is the diodes that are sensitive to short circuiting, but if the short circuiting takes place before the diodes, they can’t be damaged. And with no stator voltage, there will be very little rotor current (only what comes via the ignition light) so the stator current will rapidly subside to “not very much”.

[Dr Bob]

33 minutes ago, nicknorman said:

Actually you’ll note he says “shorting the phases out”. Ie just the windings. Although this is perhaps a bit drastic, it shouldn’t damage the alternator windings - it is the diodes that are sensitive to short circuiting, but if the short circuiting takes place before the diodes, they can’t be damaged. And with no stator voltage, there will be very little rotor current (only what comes via the ignition light) so the stator current will rapidly subside to “not very much”.

Nick, thanks for the explanation of the crowbar. A good learning experience.

I was also interested in how he was using the Rasp Pi to monitor voltages. I am using the Pi to monitor the voltage and Amps from the BMV via the Victron software on the Pi but it would be good if I could to know how to set the Pi up to read voltage directly.

[nicknorman]

10 minutes ago, Dr Bob said:

Nick, thanks for the explanation of the crowbar. A good learning experience.

I was also interested in how he was using the Rasp Pi to monitor voltages. I am using the Pi to monitor the voltage and Amps from the BMV via the Victron software on the Pi but it would be good if I could to know how to set the Pi up to read voltage directly.

The Pi doesn’t have built in analogue to digital conversion, but you can get a plug-in module to do it. This one was the first hit on google but that is not a recommendation, just an example.

https://shop.rasp.io/products/raspio-analog-zero-8-channel-analog-input-for-raspberry-pi

 

You then just need a resistor divider network to scale the battery voltage down to within the range of the AtoD converter, add the  code and you are your own uncle.

 

Edited October 21, 2019 by nicknorman

[nicknorman]

Just to add that i see the resolution of the AtoD is 10 bits, ie 1024 steps. So if the reading 1023 was made to correspond to 15v, that would give you a resolution of 0.0146v. Probably enough but there are 2 techniques to improve:

 

one is over sampling where you take multiple samples, add them up and divide by the number of samples. That chip can take 10s of thousands of samples per second. Oversampling is also a good way to reduce conversion noise (ie stop the reading from jittering)

 

Another is to span the AtoD over useful range of measurement - you perhaps only need to measure down to 9v, not interested in measuring below that. So you include a zener diode in the resistor divider network such that the first x volts doesn’t get through. 5.1v zeners are good for this since they don’t have any significant temperature coefficient.

[Dr Bob]

17 minutes ago, nicknorman said:

The Pi doesn’t have built in analogue to digital conversion, but you can get a plug-in module to do it. This one was the first hit on google but that is not a recommendation, just an example.

https://shop.rasp.io/products/raspio-analog-zero-8-channel-analog-input-for-raspberry-pi

 

You then just need a resistor divider network to scale the battery voltage down to within the range of the AtoD converter, add the  code and you are your own uncle.

 

Nick, thanks for the link and subsequent post. Very instructive. I will spend some time reading the manual for the board.

 

[mrsmelly]

Bloomin eck chaps. Whatever happened to the well tried and tested KISS principal. Why introduce huge amounts of unnecessary paraphernalia to make yer lights work 

[Dr Bob]

4 minutes ago, mrsmelly said:

Bloomin eck chaps. Whatever happened to the well tried and tested KISS principal. Why introduce huge amounts of unnecessary paraphernalia to make yer lights work 

So we don't run our engines as much?

 

[nicknorman]

6 minutes ago, mrsmelly said:

Bloomin eck chaps. Whatever happened to the well tried and tested KISS principal. Why introduce huge amounts of unnecessary paraphernalia to make yer lights work 

I wouldn't recommend kissing your batteries, it might sting a bit.

[mrsmelly]

2 minutes ago, Dr Bob said:

So we don't run our engines as much?

 

But we all have to do our bit to pollute the world innitt 

[Craig Shelley]

Sorry for the late reply... Too many hobbies

For the curious, there are a few screenshots of the monitoring system which was bodged together over a weekend using an RPI zeroW, a 24bit DelSig A/D (ADS1256) and google sheets.

For convenience i'm using a board made by WaveShare, which just plugs into the RPI and has screw terminal connectors. Cheaper clones exist.

After a year, I'm afraid this bodge has still not been turned into a proper system and parts of the circuit are still on breadboard. Despite this, it has been surprisingly reliable.

This system just monitors 3x battery currents, and the overall voltage. I would like to expand it to monitor the individual cell voltages + temperature.

Currently the cells have no means of balancing, so we occasionally do a manual spot check with a DMM. After 2 years of use, they have remained sufficiently balanced that no intervention has been needed.

From the continuous monitoring of battery current, it's possible to derive the charge and determine an estimate of the state of charge.

The data is plotted on a Google sheets chart, which can be viewed on any internet connected device with display.

This system is far from perfect, but you have to start somewhere.

 

I'll cover the alternator mods in a different post.

 

[Dr Bob]

Craig,

thanks for that. Interested to hear about how you are monitoring currents.

What cells do you have?

[peterboat]

6 minutes ago, Dr Bob said:

Craig,

thanks for that. Interested to hear about how you are monitoring currents.

What cells do you have?

Hi Bob I am feeling a right let down here, I just dont bother with my batteries, I know I should and I did on the electric truck just to make sure it was ok, but my new 36 volt batteries will have to have a new lead and connector, I am sure the software does them, but I did a voltage check the other day and the all read 40 volts ish so dont know if I can be really bothered, I have to put the new battery boxes in the stern and run the heating pipes through them so I really need to get it done this week I suppose before it gets cold.

[Dr Bob]

3 minutes ago, peterboat said:

Hi Bob I am feeling a right let down here, I just dont bother with my batteries, I know I should and I did on the electric truck just to make sure it was ok, but my new 36 volt batteries will have to have a new lead and connector, I am sure the software does them, but I did a voltage check the other day and the all read 40 volts ish so dont know if I can be really bothered, I have to put the new battery boxes in the stern and run the heating pipes through them so I really need to get it done this week I suppose before it gets cold.

Peter, I think you are doing just fine with your batteries. Just make sure you are feeding them properly. A few raisins here and ther will keep em going. Lead tends to poison most things so I would avoid that. Maybe you could relocate down to the Ionian Sea as it would be warmer there but maybe they wouldn't let you in after the end of the month?

[Tom and Bex]

@Craig Shelley Very interesting. I'd be interested to read more about your system, particularly the alternator mods and what cells you're using. 

 

Interesting you've not experienced the need to do further balancing, I know we have and @Dr Bob has had problems with cells going our of balance towards end of charge. I wonder if it's down to different charging regimes or that we're using used cells?

[Tom and Bex]

25 minutes ago, peterboat said:

I am feeling a right let down here, I just dont bother with my batteries, I know I should

Now our system has settled down and performing as we like, we don't bother with ours either. They just sit there and work! No interventions needed from us at all (other than remembering to charge them occasionally in winter!).

[Craig Shelley]

8 hours ago, mrsmelly said:

Bloomin eck chaps. Whatever happened to the well tried and tested KISS principal. Why introduce huge amounts of unnecessary paraphernalia to make yer lights work 

I totally agree. But often as we try to achieve higher performance, the complexity has a tendency to spiral upwards.

In this case I believe we are still seeing the ramifications of design decisions for automotive systems where cost would have been a very significant factor.

 

The voltage surges hadn't used to be much of a problem when the only loads were bulbs, relays, ignition coil etc...

The radio was more sensitive, and It was far more cost effective to build the surge protection into the radio rather than into the alternator.

As time has moved on, there are now many electronic gadgets connected to the 12V supply. The automotive industry decided that every device connected to the supply should incorporate the surge protection, and published standards such as ISO-16750 to define the test scheme. It's quite a harsh set of tests, one of which (load-dump) defines a pulse of over 100V.

 

The only problem is that the market is now flooded with a lot of cheep kit which won't come close to meeting these specs. e.g. knock-off mobile phone chargers.

The industry has started to recognise that designing the surge protection into every device is no longer a cheap get-out, and the problem needs to be remedied at source. The next generations of vehicle alternators therefore, inevitably will be more complex.

[Richard10002]

Just watched the first half of a Wheeler Dealers episode in the US, where they had bought a 1985 Maserati Bi Turbo which had been converted to electric.

 

They were speaking to a company that repurposes electric car batteries and retrofits electric motors - they also talked of controllers. I wonder if there are such companies here yet... or are they coming soon? Presumably it's as easy to drop repurposed electric car batteries into a boat, rather than a car. They said that they would get the same power from 76kg of Lithium Batteries as half a ton of Trojan LA batteries.

 

Everything being discussed in this thread seems to be pretty much DIY, requiring a knowledge of lots of stuff that the ordinary Joe doesn't know. Hard to see it taking off until you can buy batteries and a gizmo or two that you can just connect with a few wires without knowing how it all works?

[mrsmelly]

7 hours ago, Richard10002 said:

Just watched the first half of a Wheeler Dealers episode in the US, where they had bought a 1985 Maserati Bi Turbo which had been converted to electric.

 

They were speaking to a company that repurposes electric car batteries and retrofits electric motors - they also talked of controllers. I wonder if there are such companies here yet... or are they coming soon? Presumably it's as easy to drop repurposed electric car batteries into a boat, rather than a car. They said that they would get the same power from 76kg of Lithium Batteries as half a ton of Trojan LA batteries.

 

Everything being discussed in this thread seems to be pretty much DIY, requiring a knowledge of lots of stuff that the ordinary Joe doesn't know. Hard to see it taking off until you can buy batteries and a gizmo or two that you can just connect with a few wires without knowing how it all works?

Nail on head.