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Dr Bob

Another Lithium battery thread

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7 minutes ago, nicknorman said:

Yes it does use a bit of juice, although when the measured current is zero it’s not massive. But the differential supply and output swing is a bit of a pain. The differential output can be dealt with by a fairly simple circuit but not sure how that would affect the critical zero point accuracy.

 

If i we’re doing it I think I would use a shunt and digitise the value locally, send it via CANBUS etc to the main control system (all done with a PIC, obviously!). Which of course is exactly what my Mastervolt Mastershunt does (so I don’t claim any originality!)

 

Incidentally I just sent off my PCB files to China, £29 for 10 boards 75mm x 50mm on 48 hr production and 2-3 days delivery. We’ll see what happens!

Let me know how the PCBs go. I have no experience of surface mount and I believe there are a few new things to understand (relating to surface tension and the like) when laying out the board. However at those prices its not a disaster if it takes two shots to get it right.

 

There are a couple of neat little shunt ICs that do all the amplification and ADC and send the result over an I2C bus, I suspect these are what are used in the various active shunts.  INA220 is one of them.

 

...............Dave

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22 minutes ago, dmr said:

Let me know how the PCBs go. I have no experience of surface mount and I believe there are a few new things to understand (relating to surface tension and the like) when laying out the board. However at those prices its not a disaster if it takes two shots to get it right.

 

There are a couple of neat little shunt ICs that do all the amplification and ADC and send the result over an I2C bus, I suspect these are what are used in the various active shunts.  INA220 is one of them.

 

...............Dave

AIUI surface tension is only an issue whilst actually reflowing, and mostly for any components on the underside (which might fall off). I don’t have any components on the underside! At a pinch I think one can glue components down, but when I reflowed this board (that’s the tiny sensor I posted a pic of earlier, and a couple of decoupling caps) I just kept the airflow rate slow and there was no tendency for them to get blown around. I guess it depends on pad area vs windage of component. Of course with a proper solder mask it will be much easier (I hope!). I’ve decided to use 1206 passives which are relatively large (but still tiny!)

95588183-F218-4D15-AF9D-B627910D78CD.jpeg.e432fe83cce8d36707da2b3a1f25eb4a.jpeg

 

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Oh and while I’m on, this is the top copper and silkscreen layers of the board I’ve sent for manufacture. Board is 76 x 50mm. Checked endlessly but no doubt something will be wrong!

 

19A1A73A-0A55-4F5B-AF08-2A6C31E48D66.jpeg.725e95139a610b4f6151a500410221b5.jpeg

 

 

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Looks good to me.

 

I imagine its much harder to correct things on surface mount. On some of my one-off instruments if I had any space I put a bit of "veroboard" style stuff in the spare space so I could retrofit an op amp or a TTL/CMOS logic chip or whatever.

 

I always used the thickest tracks that I could fit in but accurate analog stuff was my thing, it matters a lot less with digital.....but its always sad to pay for copper and then get it etched away 😀.

 

...................Dave

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On 09/01/2019 at 22:19, Dr Bob said:

Thanks for all of that T&B. Have a greenie.

Yes, great info. I like the idea of the 12.8V and 14.0v cutoffs plus the cell monitoring. A cheap solution and worth a try. I hadnt thought of sensing from the lead acid but now that seems obvious so it connects again.

 @peterboat can you give me info on your 6 squid controller from Amazon? That sounds realy useful.

Bob I cant find my bill buying the board from Amazon, the board is installed and no visible part no to be seen I will look on amazon for it 😞

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14 minutes ago, dmr said:

Looks good to me.

 

I imagine its much harder to correct things on surface mount. On some of my one-off instruments if I had any space I put a bit of "veroboard" style stuff in the spare space so I could retrofit an op amp or a TTL/CMOS logic chip or whatever.

 

I always used the thickest tracks that I could fit in but accurate analog stuff was my thing, it matters a lot less with digital.....but its always sad to pay for copper and then get it etched away 😀.

 

...................Dave

The bottom side has copper fill, separated into digital and analogue grounds so not much gets etched away:D. This circuit is virtually entirely digital with the 3 pressure sensors and the remote temperature sensor all having digital outputs (I2C and Onewire) so hopefully it will just "work" as the current lashup on breadboard does! Hopefully the groundplane and separate digital and analogue 3v3 regulators will help to reduce noise on the barometric pressure sensors which need to be super un-noisy. Output is from 200 to 1200 hPa and jitter of 0.01hPa is too much!

Edited by nicknorman

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3 minutes ago, nicknorman said:

The bottom side has copper fill, separated into digital and analogue grounds. This circuit is virtually entirely digital with the 3 pressure sensors and the remote temperature sensor all having digital outputs (I2C and Onewire) so hopefully it will just "work" as the current lashup on breadboard does! Hopefully the groundplane and separate digital and analogue 3v3 regulators will help to reduce noise on the barometric pressure sensors which need to be super un-noisy. Output is from 200 to 1200 hPa and jitter of 0.01hPa is too much!

Its good to learn something new. I've mostly worked in sound and vibration so pressure measurement is pretty central, but I've never come across the hPa before!!!!

Its not really a preferred SI thing, is it an aircraft unit? I can see that its useful as its a millibar. Pressure has always been a bit of a rogue quantity with Newton per square meter, Pascals and Bars all getting used   and even mmHg.

 

I reckon 0.01hPa is quite a challenge.

 

..............Dave

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19 minutes ago, dmr said:

Its good to learn something new. I've mostly worked in sound and vibration so pressure measurement is pretty central, but I've never come across the hPa before!!!!

Its not really a preferred SI thing, is it an aircraft unit? I can see that its useful as its a millibar. Pressure has always been a bit of a rogue quantity with Newton per square meter, Pascals and Bars all getting used   and even mmHg.

 

I reckon 0.01hPa is quite a challenge.

 

..............Dave

Yes it is the same unit as millibars but at some point about 10 years ago, ICAO (international civil aviation organisation) decided that us pilots and ATC would all have to call it hectopascals not millibars. I've no idea why! Some bureaucratic ivory tower perfection-seeker I expect - he probably decided that the pascal was the SI unit, not the bar. After 10 years I've nearly got used to it!

The sensor does oversampling internally - up to 4096 times, which takes it 8 mS, and thus has an apparent 24 bit resolution. I've made sure there is no I2C bus activity whilst that is happening.

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13 hours ago, peterboat said:

Bob I cant find my bill buying the board from Amazon, the board is installed and no visible part no to be seen I will look on amazon for it 😞

That's great Peter. Let me know if you find the order details in your amazon account. No rush but keen to see what you bought. Not far off making a decision soon.

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On 11/01/2019 at 13:03, WotEver said:

I think that is better than mine!! it comes in a nice box and has a bigger voltage range in fact I might order one just in case

On 11/01/2019 at 12:48, Dr Bob said:

That's great Peter. Let me know if you find the order details in your amazon account. No rush but keen to see what you bought. Not far off making a decision soon.

Look at Tonys link it looks very tidy and internally the same as mine

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On 11/01/2019 at 13:03, WotEver said:

Jeesus guys!! are you suggesting protecting thousands of pounds worth of kit with a ten quid gadget from China? I am following this thread on and off to get some ideas for when in twenty years time the technology is good enough to fit Lithiums but didnt realise in all honesty some of the bits of kit you were discussing were so cheap?!!

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46 minutes ago, mrsmelly said:

Jeesus guys!! are you suggesting protecting thousands of pounds worth of kit with a ten quid gadget from China? I am following this thread on and off to get some ideas for when in twenty years time the technology is good enough to fit Lithiums but didnt realise in all honesty some of the bits of kit you were discussing were so cheap?!!

Yes, I was a little concerned over that but the system will have another disconnect based on individual cell voltage ....however this has to be reliable.

How do you wire it up. I assume the +ve/-ve to the battery is as it says. Is then the +ve/-ve to the charge source the circuit that opens and closes to power a relay that then works the diconnect switch. What type of relay would I need and what type of switch. I think I need to spend a bit of time researching the relay and disconnect side of things!

Thanks to all for identifying this board.

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On 06/01/2019 at 15:57, nicknorman said:

Could someone please remind me what the reasonably priced source of these second hand batteries that people are using is please?

Nick, have a word with Peterboat or JohnV

Phil

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The beasts have arrived, and were getting in the way, so I've snuggled them into their new home under the bed. The strange cross arrangement is a stand for storing the cratch board during the summer, and is much too solidly engineered to be made removable, so I've had to make the side of the battery box demountable to get them in and out. The space at the side is protected at the front and will also have a top piece for protection. That will be the location of the contactor and electronics.

 

MP

 

 

 

IMG_20190114_170805856.jpg

IMG_20190114_170842718.jpg

IMG_20190114_131753925.jpg

Edited by MoominPapa
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Outstanding MP. I wondered how the 2* packs of 6 cells would be organised.

I'd not thought about putting them under the bed. How far away is that from your charge sources - ie solar and alternator? Easy to build a wooden frame.

Keep us posted  on how you get on.

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Great stuff MP my domestics live under the steps coming down from the stern, they have central heating pipes to keep them warm 😎 the drive batteries live in the well where the engine lived, because water down that deep doesnt freeze, and they are insulated they should be ok, and sit at about 4 degrees or so in the winter.

Ps I worried about getting my batteries out but in reality they are there to stay and if you are like me the box wont be opened unless it to get something else out of storage

On 13/01/2019 at 11:07, Dr Bob said:

Yes, I was a little concerned over that but the system will have another disconnect based on individual cell voltage ....however this has to be reliable.

How do you wire it up. I assume the +ve/-ve to the battery is as it says. Is then the +ve/-ve to the charge source the circuit that opens and closes to power a relay that then works the diconnect switch. What type of relay would I need and what type of switch. I think I need to spend a bit of time researching the relay and disconnect side of things!

Thanks to all for identifying this board.

My board cost less!! but in practice the batteries are fine without all the stuff to protect them, or they are unless a solar panel goes down 😟

Edited by peterboat
  • Greenie 2

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43 minutes ago, Dr Bob said:

Outstanding MP. I wondered how the 2* packs of 6 cells would be organised.

I'd not thought about putting them under the bed. How far away is that from your charge sources - ie solar and alternator? Easy to build a wooden frame.

Keep us posted  on how you get on.

The bulkhead they're next to is the engine room, and all the high current cables are in a cupboard literally just behind the batteries, the other side of the bulkhead. In the bottom of that cupboard there's also the dry-sump engine's oil tank, which contains 20l of engine oil at 80 Celsius by the end of a days running, which is why the batteries are spaced away from the bulkhead and I added some of the stick-on silver bubble-wrap insulation. 

 

You can see that all the cell interconnects are horribly vulnerable to shorts: it's essential to have a well fitting, non-conducting lid over the cells, especially as we use that space for general, and generally quite messy, storage.

 

MP.

 

ETA. The old battery space, under the engine room floor, will become a ready-access tool locker. It's much more useful storage than what we're giving up under the bed to store the new batteries. The normal access is from the end of the bed, so that space is normally right at the back of a six-foot deep hole. Plus, when the cratch is there, it's not accessible even by lifting the mattress and removing the bed slats.

Edited by MoominPapa

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4 minutes ago, MoominPapa said:

The bulkhead they're next to is the engine room, and all the high current cables are in a cupboard literally just behind the batteries, the other side of the bulkhead. In the bottom of that cupboard there's also the dry-sump engine's oil tank, which contains 20l of engine oil at 80 Celsius by the end of a days running, which is why the batteries are spaced away from the bulkhead and I added some of the stick-on silver bubble-wrap insulation. 

 

You can see that all the cell interconnects are horribly vulnerable to shorts: it's essential to have a well fitting, non-conducting lid over the cells, especially as we use that space for general, and generally quite messy, storage.

 

MP.

 

All good, my domestics are strapped down,  the drive batteries have a wooden lid because of the same lead problems which could short, the batteries are a tight fit as well

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On 13/01/2019 at 11:07, Dr Bob said:

I think I need to spend a bit of time researching the relay and disconnect side of things!

I think this is one of the most difficult areas to come up with a reliable, low power consumption yet cost effective solution. 

 

 

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For those of an electronic disposition I will just mention that the PCBs I designed (using free DesignSpark software) took 6 days to turn around from Elecrow in China. Total cost for 10 boards, £29. Which I think is exceptionally good. Quality is fine. So getting proper PCBs made up for home projects is perfectly feasible. I chose to use mostly surface mount as I’ve found it easy to solder components using a hot air rework station and solder paste.

 

4211EFCF-60F9-4D89-8B10-6F1E2B683A97.jpeg.84176da6933d5b2f6ff92ba93c230556.jpeg

 

23134483-24FA-4F08-8439-09279AA49139.jpeg.9ddbbf54bd365546c930a5cda81f0454.jpeg

 

and here with some components soldered on...

 

9009F868-6D43-4B08-BED2-622E430AEA5F.jpeg.7ac0951bda6a3d9adcfad66fb160def0.jpeg

  • Greenie 2

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26 minutes ago, nicknorman said:

For those of an electronic disposition I will just mention that the PCBs I designed (using free DesignSpark software) took 6 days to turn around from Elecrow in China. Total cost for 10 boards, £29. Which I think is exceptionally good. Quality is fine. So getting proper PCBs made up for home projects is perfectly feasible. I chose to use mostly surface mount as I’ve found it easy to solder components using a hot air rework station and solder paste.

 

4211EFCF-60F9-4D89-8B10-6F1E2B683A97.jpeg.84176da6933d5b2f6ff92ba93c230556.jpeg

 

23134483-24FA-4F08-8439-09279AA49139.jpeg.9ddbbf54bd365546c930a5cda81f0454.jpeg

 

and here with some components soldered on...

 

9009F868-6D43-4B08-BED2-622E430AEA5F.jpeg.7ac0951bda6a3d9adcfad66fb160def0.jpeg

What's the structure above R2, which seems to almost, but not quite, separate the two ground planes?

 

MP.

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4 minutes ago, MoominPapa said:

What's the structure above R2, which seems to almost, but not quite, separate the two ground planes?

 

MP.

Yes there are two “separate” ground planes on the underside, one for the digital and one for the analogue. They join at that point simply by having 2 overlapping pads. There is a pin soldered in there, temporarily for test purposes.

Although of course the “analogue” pressure sensors have digital (I2C) outputs, so I just wanted to try to minimise noise in the vicinity of the actual sensors. When the 24 bit AtoD process is ongoing (10mS or so) I take care to avoid any I2C bus activity.

 

Noisiest thing I’m sure is the MAX3232 which uses charge pumps to generate +-5v from the 3v3 supply, for the RS232 interface. That is far left of the board.

 

Anyway good news is that the processor runs fine. I do have a problem with one of the sensors not working, I’ve taken it off and on again and can’t see a soldering issue so I think it must be duff. Third sensor is much bigger and through hole, yet to be soldered in and I have run out of time as leaving for the airport shortly to fly down to the boat (snow in Aberdeen permitting!)

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