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Another Lithium battery thread


Dr Bob

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1 hour ago, Dr Bob said:

The midnites seem to be well over the top for me. I only have 500W of power so looking for an MPPT that can cope with 40A max.

 

The two controllers I have now my be ok as long as they dont hold at the max voltage for a lengthy absorbtion period. I cant find any info on the Victron site about how far the voltages can be adjusted or how long it will hold at an adsorption voltage.

They do smaller ones Bob have a peruse on the site

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17 minutes ago, Dr Bob said:

In the morning I will turn the manual isolation switch off...

Until the day that you forget and then wave bye-bye to your Lithiums. 

 

Automate everything is my advice. 

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9 minutes ago, WotEver said:

Until the day that you forget and then wave bye-bye to your Lithiums. 

 

Automate everything is my advice. 

Or interlock the LFP disconnect with the starter feed in such a way that it is impossible to start the engine with the LFPs connected.  If you forget, you can't run the alternator.

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13 minutes ago, TheBiscuits said:

Or interlock the LFP disconnect with the starter feed in such a way that it is impossible to start the engine with the LFPs connected.  If you forget, you can't run the alternator.

Yup. Anything that doesn’t require memory. 

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2 hours ago, WotEver said:

Until the day that you forget and then wave bye-bye to your Lithiums. 

 

Automate everything is my advice. 

Well no, that wont happen.

If I forget to disconnect, then when I start the engine, the lithiums will get a charge from the alternator. I ALWAYS watch the charge on the alternator via the bluetooth BMV 712 when motoring so will immediately see the alternator is connected. If I dont, then the lithiums will charge from the Alternator. If (and it is an if) the voltage gets to 14.1V then the alarm on the BG -BS8 will sound. When it gets to 14.2V the alarm on the BMV712 will sound. When an individual cell gets to 3.8V the Aus unit will physically disconnect the bank. If an individual cell gets to 3.8V whilst the total bank is below 14.1V  (ie it spends an hour or more in absorption at 14.0V and we get into the knee) then there will be no alarms but it will auto disconnect. I will also wire the BMV to disconnect on high voltage if someone can help me with the circuit.

My biggest worry in your scenario is that the alternator overheats due to delivering 80A (rated 90A) for an hour or more. For this I have the Sterling AtoB which stops its voltage adjustment if the alternator goes over 90°C so I have a chance of seeing the voltage change from the alternator - I use a mobile phone visible from the steering position to monitor battery charging. This is what I want to look at during the summer - how the alternator interacts with the system. It may well be that I never get above 80% SOC with the alternator and it doesnt get too hot.

I did think about having a disconnect relay powered from the ignition switch so I cant charge the lithiums from the alternator and I will review this if high temps or long absorption times will cause me an issue.

Worst case then is I burn out some alternator components. Good excuse to buy a decent alternator and controller.

I do agree with your 'Automate everything' but this is one case where I will do it manually. Everytime I take the boat out, I check the phone app to see the charge voltage to make sure the AtoB kicks in. I have NEVER not done that in the 18 months since the AtoB has been fitted. That then is the trigger to make sure the connect is turned off.

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Every day is a school day.

 

Having installed wired the batteries, and taken the Ardunio-BMS system from my test setup with 3.5AH cells, to the real thing, I've spent half of today chasing done a dodgy connection in the connector to the monitor display. This shouldn't have taken anything like as long as it did, but I added lashings of stupidity and chased several blind alleys. Got there in the end. Everything working. Sensible voltage and temperature readings. The whole works.

 

So the final test. Connect the heavy cable to the Lihtium positive terminal. Tell the BMS to close the contactor and parallel the Lithiums. Contactor closes. Arduino crashes and starts to reboot. Fail-safe circuit, having lost communication with the Arduino, opens contactor. Arduino restarts, and closes contactor. Rinse and repeat.

 

After some poking around, it's clear that the inrush when the contactor closes is causing the problem. It seems I need something called a precharge circuit. https://en.wikipedia.org/wiki/Pre-charge. I had thought about this, but given that everything is already at 12v or thereabouts from the start battery,  I assumed I wouldn't need it. Turns out I do. If I connect my experimental load-bank, which is three 12v 10W tungsten lamps in parallel, across the contactor contacts whilst it's closing, all is good, and the Arduino doesn't crash.

 

Those cells have crazy low impedance.

 

So I need a reasonably meaty resistor and a relay controlled by the computer to connect the resistor across the contactor contacts a few hundred ms before it closes.

 

I feel a Farnell order coming on!

 

MP.

 

 

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6 minutes ago, MoominPapa said:

Every day is a school day.

 

Having installed wired the batteries, and taken the Ardunio-BMS system from my test setup with 3.5AH cells, to the real thing, I've spent half of today chasing done a dodgy connection in the connector to the monitor display. This shouldn't have taken anything like as long as it did, but I added lashings of stupidity and chased several blind alleys. Got there in the end. Everything working. Sensible voltage and temperature readings. The whole works.

 

So the final test. Connect the heavy cable to the Lihtium positive terminal. Tell the BMS to close the contactor and parallel the Lithiums. Contactor closes. Arduino crashes and starts to reboot. Fail-safe circuit, having lost communication with the Arduino, opens contactor. Arduino restarts, and closes contactor. Rinse and repeat.

 

After some poking around, it's clear that the inrush when the contactor closes is causing the problem. It seems I need something called a precharge circuit. https://en.wikipedia.org/wiki/Pre-charge. I had thought about this, but given that everything is already at 12v or thereabouts from the start battery,  I assumed I wouldn't need it. Turns out I do. If I connect my experimental load-bank, which is three 12v 10W tungsten lamps in parallel, across the contactor contacts whilst it's closing, all is good, and the Arduino doesn't crash.

 

Those cells have crazy low impedance.

 

So I need a reasonably meaty resistor and a relay controlled by the computer to connect the resistor across the contactor contacts a few hundred ms before it closes.

 

I feel a Farnell order coming on!

 

MP.

 

 

For my motor controller, which is a Curtis speed control, I have to connect a 250 ohm 5 watt resistor across the solenoid  that powers it up, so that on start up it prevents "problems", what those problems are I have no idea? but rather than damage something expensive....................

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21 minutes ago, MoominPapa said:

I feel a Farnell order coming on

MP, I read about pre-charge circuits in the REC BMS info.

http://www.rec-bms.com/BMSSMA.html

In the Aus BMS unit that T&B are using

http://www.zeva.com.au/Products/datasheets/BMM8v2_Manual.pdf

they talk about voltage spikes viz

Be sure to add spike suppression diodes (as shown in the diagram) such as a 1N4004 across any relay coils to suppress inductive voltage spikes which can damage SSRs.

Is that the same thing? Is the diode working the same way as the resistor?

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6 minutes ago, Dr Bob said:

MP, I read about pre-charge circuits in the REC BMS info.

http://www.rec-bms.com/BMSSMA.html

In the Aus BMS unit that T&B are using

http://www.zeva.com.au/Products/datasheets/BMM8v2_Manual.pdf

they talk about voltage spikes viz

Be sure to add spike suppression diodes (as shown in the diagram) such as a 1N4004 across any relay coils to suppress inductive voltage spikes which can damage SSRs.

Is that the same thing? Is the diode working the same way as the resistor?

I discovered that RS were a lot cheaper than Farnel

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2 minutes ago, Dr Bob said:

MP, I read about pre-charge circuits in the REC BMS info.

http://www.rec-bms.com/BMSSMA.html

In the Aus BMS unit that T&B are using

http://www.zeva.com.au/Products/datasheets/BMM8v2_Manual.pdf

they talk about voltage spikes viz

Be sure to add spike suppression diodes (as shown in the diagram) such as a 1N4004 across any relay coils to suppress inductive voltage spikes which can damage SSRs.

Is that the same thing? Is the diode working the same way as the resistor?

 

The first on is the same, their contactor has a pre-charge function.

 

The second isn'.t When a relay coil is turned OFF, the energy stored in the magetic field gets turned back into electricity, and a voltage momentarily appears across the coil terminals. This can be quite high,enough to do damage, to the transistor driving the coil, but fortunately it's in the opposite sense to the supply voltage, so a diode connected in the correct direction across the coil will shunt the spike. but be reverse-biased and non-conducting when the relay is on. It's a very standard technique. Many 12v automotive relays have the diode built-in.

 

MP.

 

 

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1 minute ago, MoominPapa said:

 

The first on is the same, their contactor has a pre-charge function.

 

The second isn'.t When a relay coil is turned OFF, the energy stored in the magetic field gets turned back into electricity, and a voltage momentarily appears across the coil terminals. This can be quite high,enough to do damage, to the transistor driving the coil, but fortunately it's in the opposite sense to the supply voltage, so a diode connected in the correct direction across the coil will shunt the spike. but be reverse-biased and non-conducting when the relay is on. It's a very standard technique. Many 12v automotive relays have the diode built-in.

 

MP.

 

 

Thanks for that. As you say, school every day!

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To add to my post of yesterday, here is the proposed diagram. I'm happy with the solution to Wotever's advice on automating the manual switch ...which I may do via 12V from the ignition circuit if the alternator is a problem. I will certainly keep an eye on that. Thanks for the input.

 

A few questions:

1) Can I activate the auto disconnect (the BEP motorised switch) via two relay sources...ie the green dotted lines on the diagram (and maybe a 3rd relay source if I fit a temperature control board)?

2) Could I use a Tyco latching relay (below) instead of the BEP motorised switch without a complicated circuit if it doesnt need to auto reset, ie in the event of an emergency disconnect, I want to manually reset it. Can someone come up with a circuit I could use for this?

3) The idea of piggybacking the Li's onto the LA circuit (in the first post in this thread) looks good to protect charging devices in the event of emergency disconnect. Is there though an issue on reconnection if the LA bank is at low SOC (it shouldnt be...... but if it is?). Would too much current flow from the Li bank to the LA bank? The solution then is just remove most of the LA's but I wont do this straight away. Any thoughts?

Screen Shot 2019-02-02 at 14.36.26.png

Screen Shot 2019-02-02 at 14.38.37.png

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On 02/02/2019 at 14:53, Dr Bob said:

 

 

A few questions:

1) Can I activate the auto disconnect (the BEP motorised switch) via two relay sources...ie the green dotted lines on the diagram (and maybe a 3rd relay source if I fit a temperature control board)?

2) Could I use a Tyco latching relay (below) instead of the BEP motorised switch without a complicated circuit if it doesnt need to auto reset, ie in the event of an emergency disconnect, I want to manually reset it. Can someone come up with a circuit I could use for this?

3) The idea of piggybacking the Li's onto the LA circuit (in the first post in this thread) looks good to protect charging devices in the event of emergency disconnect. Is there though an issue on reconnection if the LA bank is at low SOC (it shouldnt be...... but if it is?). Would too much current flow from the Li bank to the LA bank? The solution then is just remove most of the LA's but I wont do this straight away. Any thoughts?

 

Bump....

Any ideas?

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43 minutes ago, Dr Bob said:

Bump....

Any ideas?

As far as 2) is concerned, the answer is yes, but it depends on your definition of "complicated". You just need a monostable circuit and a MOSFET to drive the coil. I'd offer to run up something, but I have 8 days before I leave my winter moorings, and set of lithium batteries to commission..... I could provide you a hand-drawn, unstested circuit diagram if that would help.

 

I'd worry about 3). In fact I did, but in my case it was easy, a bit of code that says not to connect tthe batteries when the voltage difference is too high.

 

MP.

 

 

MP.

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Late to the party on this and frantically reading.

 

What are the main safety concerns with these batteries compared to LA. What are their failure mode, are they likely to catch fire and set light to my bed. Are there any insurance company issues installing a home brew lithium power source?  Are they likely to be covered in the boat safety scheme in the future?

 

Sorry if these questions have already been covered (feel free to ignore, I am sure I will stumble across them)

Edited by rusty69
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3 hours ago, MoominPapa said:

As far as 2) is concerned, the answer is yes, but it depends on your definition of "complicated". You just need a monostable circuit and a MOSFET to drive the coil. I'd offer to run up something, but I have 8 days before I leave my winter moorings, and set of lithium batteries to commission..... I could provide you a hand-drawn, unstested circuit diagram if that would help.

 

I'd worry about 3). In fact I did, but in my case it was easy, a bit of code that says not to connect tthe batteries when the voltage difference is too high.

Thanks Simon.

If you have the time to do a hand drawn diagram that would be great. I've ordered the BEP motorised switch as per T&B's set up but interested to se how to wire the Tyco switch. Only do it if you have time.

On (3), OK. I guess if the LA bank is over 80% charged then it wont take that much current if the contactor to the Li bank is linked. I could therefore have a 12.5V lower limit set on the LA's BMV 712 to isolate the Lithium bank via the auto disconnect.

So that brings us back to (1) - can I control the auto disconnect switch (the BEP motorised switch) from 3 different devices (ie the 2 BMV 712s and the Australian BMS cell monitoring device)?

 

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24 minutes ago, rusty69 said:

Late to the party on this and frantically reading.

 

What are the main safety concerns with these batteries compared to LA. What are they're failure mode, are they likely to catch fire and set light to my bed. Are there any insurance company issues installing a home brew lithium power source?  Are they likely to be covered in the boat safety scheme in the future?

 

Sorry if these questions have already been covered (feel free to ignore, I am sure I will stumble across them)

If we ignore the potential failure modes that wreck the batteries ie over voltage (too high charging) or under voltage (or charging below 0°C) - which can render you expensive purchase less use than a brick - the prime safety concern is the potential fire or explosion risk on trying to stuff too much voltage in. LiFePo4 batteries however seem to be at the safer end of the Lithium battery types and I am not that sure there have been any serious failures in boats causing major fires etc. It is still vital that you dont let individual cell voltage to go over 4.0V and your cells need to be 'clamped' in a brace so that there is a resistance to them swelling/distorting.

My strategy for avoiding this case is to have 2 independent sets of audible alarms and an auto disconnect - activated by one of 2 separate circuits. I am wondering if I should have a second auto disconnect in the line for another level of redundancy. I will also monitor the temp of the bank with audible alarm and an autodisconnect. Typically the charging sources should be set to a level where they cannot damage the setup and the alarms and disconnects only work in emergency.

Another issue on boats is the physical strength of the batteries. On a NB, the demand is not high but I can see 'fragile' Lithiums on a lumpy water boat getting exposed to lots of vibration and bangs particularly if the skipper it prone to beating often (when we crusied we had a rule - never beat into more than a force 4! - bit different to when we raced). Mechanical failure could lead to cell short circuits and voltage issues. It sounds like buying good quality cells (ie Winston) that will give you decent mechanical performance which should (will?) be ok for an NB.

Having spent the last 3 months reading everything I could on the subject, I am happy to install a DIY system but there is no way I would install any lithium system (even an all singing all dancing Victon £6K one) if I expected it to be plug and play and I didnt understand batteries and charging etc. Electronic circuits fail and all the redundancy in the world may not be enough without good supervision.

Your post is a good one and make you think. As a result, I will do a risk review in the next few days on what I am proposing (ie a traditional Hazop) and see what that raises.

On the insurance issue, I checked by schedule and there is no mention of Lithium batteries. Not sure if anyone else has seen a problem here.

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7 minutes ago, Dr Bob said:

My strategy for avoiding this case is to have 2 independent sets of audible alarms and an auto disconnect - activated by one of 2 separate circuits <snip>

Thanks Dr Bob for the detailed reply. So will you continue to charge the cells whilst away from the boat, or manually disconnect them from the solar, or rely on the auto disconnect? I assume you won't hear the audible alarms whilst in Singapore.

 

Also, any special fire extinguisher installation fitted beneath the bed? I don't want to set fire to Mrs Rusty.

 

As you can see, I at the beginning of the journey. Pity Mtb stopped posting, I think he purchased some LiFePo4's.

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1 minute ago, rusty69 said:

Thanks Dr Bob for the detailed reply. So will you continue to charge the cells whilst away from the boat, or manually disconnect them from the solar, or rely on the auto disconnect? I assume you won't hear the audible alarms whilst in Singapore.

 

Also, any special fire extinguisher installation fitted beneath the bed? I don't want to set fire to Mrs Rusty.

 

As you can see, I at the beginning of the journey. Pity Mtb stopped posting, I think he purchased some LiFePo4's.

Charging while away from boat.

For the first few months if I am away overnight, I will manually disconnect the Lithium bank and allow the LA's to be charged by the solar or on shore power. Also for the first few months I will manually disconnect if we go to the pub.....as i do with most of the panel switches. Leaving the LA bank in place, I will have good flexibility here until I learn the Lithium system and I can turn off the Lithiums when I like (as long as they are not near 100% SoC and best around 50% SoC).

One potential failure mode is a solar controller going wrong and allowing 40V+ to the battery circuit. Not good if we are in the pub. It does drive me to having two separate disconnects in the circuit rather than one.

This all sounds like a lot of faffing around! Yes, but I like faffing with batteries and it will avoid running the engine for hours as we do now.

Not sure a fire extinguisher will work if the LiFePo4 catches fire.

A good source of info is

https://marinehowto.com/lifepo4-batteries-on-boats/

 

 

 

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39 minutes ago, rusty69 said:

Thanks Dr Bob for the detailed reply. So will you continue to charge the cells whilst away from the boat, or manually disconnect them from the solar, or rely on the auto disconnect? I assume you won't hear the audible alarms whilst in Singapore.

 

Also, any special fire extinguisher installation fitted beneath the bed? I don't want to set fire to Mrs Rusty.

 

As you can see, I at the beginning of the journey. Pity Mtb stopped posting, I think he purchased some LiFePo4's.

 

I know you asked Dr Bob the question, but this is my answer. I won't be charging the LiFePO4 cells using solar when off the boat, and with everything shut down. The reason being that lithium cells like to be stored at a moderate state of charge, and not floated. When leaving the boat I will endeavour to get the Lithiums at the 40% to 50% SOC they like, then open the paralleling contactor and isolate them, leaving the solar to keep the start lead-acid battery fully charged and floated, which it likes.

 

MP

 

ETA. No fire extiguisher under the bed. In the event that the batteries go up, I figure I want to be where I notice ASAP. 

 

The fire characteristics of these things are actually quite good. If they short, all the energy goes into making them hot, like any battery, So you have to worry about them setting their surroundings on fire. The main hazard from the batteries themselves is that they will vent the electrolyte from the emergency vents as a vapour and said electrolyte is a flamable hydrocarbon.  At least it's not an explosive gas, like lead-acids emit.

 

 

 

Edited by MoominPapa
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On 01/02/2019 at 16:44, MoominPapa said:

Every day is a school day.

 

Having installed wired the batteries, and taken the Ardunio-BMS system from my test setup with 3.5AH cells, to the real thing, I've spent half of today chasing done a dodgy connection in the connector to the monitor display. This shouldn't have taken anything like as long as it did, but I added lashings of stupidity and chased several blind alleys. Got there in the end. Everything working. Sensible voltage and temperature readings. The whole works.

 

So the final test. Connect the heavy cable to the Lihtium positive terminal. Tell the BMS to close the contactor and parallel the Lithiums. Contactor closes. Arduino crashes and starts to reboot. Fail-safe circuit, having lost communication with the Arduino, opens contactor. Arduino restarts, and closes contactor. Rinse and repeat.

 

After some poking around, it's clear that the inrush when the contactor closes is causing the problem. It seems I need something called a precharge circuit. https://en.wikipedia.org/wiki/Pre-charge. I had thought about this, but given that everything is already at 12v or thereabouts from the start battery,  I assumed I wouldn't need it. Turns out I do. If I connect my experimental load-bank, which is three 12v 10W tungsten lamps in parallel, across the contactor contacts whilst it's closing, all is good, and the Arduino doesn't crash.

 

Those cells have crazy low impedance.

 

So I need a reasonably meaty resistor and a relay controlled by the computer to connect the resistor across the contactor contacts a few hundred ms before it closes.

 

I feel a Farnell order coming on!

 

MP.

 

 

 

Update on this. The precharge function is not necessary, my first design was right in that respect. Even bridging the contactor with a wire doesn't generate serious sparks, so there's no much energy moving when the lithiums come on line. I don't have the test equipment to diagnose this absolutely, but my guess is that the change in voltage to the Arduino supply is not a problem, by dV/dt is. The supply is picked of right at the contactor, so the impedance to  the batterries is very low. I'm using a little switch mode 12v to 5v PSU for the Arduino. The specs say it doesn't need any filtering on the input, but the very rapid change in voltage looks to be triggering the protection circuits. I put an RC filter on the PSU input, consisting of a 7 ohm resistor, and 1000uF and 0.1uF capacitors to ground. The Ardunio only uses about 60mA so I can easily afford the voltage drop over the resistor.

 

This has fixed the processor resetting  when going online problem completely.

 

Phew. Onwards!

 

MP.

 

 

 

 

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1 hour ago, Dr Bob said:

Good link Dr Bob (I have read it in the past iirc),The video of the chinamen abusing a set of cells gives me a bit more confidence should all these safety cut outs fail.

58 minutes ago, MoominPapa said:

 

I know you asked Dr Bob the question, but this is my answer. I won't be charging the LiFePO4 cells using solar when off the boat, and with everything shut down. The reason being that lithium cells like to be stored at a moderate state of charge, and not floated. When leaving the boat I will endeavour to get the Lithiums at the 40% to 50% SOC they like, then open the paralleling contactor and isolate them, leaving the solar to keep the start lead-acid battery fully charged and floated, which it likes.

 

MP

 

ETA. No fire extiguisher under the bed. In the event that the batteries go up, I figure I want to be where I notice ASAP. 

 

The fire characteristics of these things are actually quite good. If they short, all the energy goes into making them hot, like any battery, So you have to worry about them setting their surroundings on fire. The main hazard from the batteries themselves is that they will vent the electrolyte from the emergency vents as a vapour and said electrolyte is a flamable hydrocarbon.  At least it's not an explosive gas, like lead-acids emit.

 

 

 

Thanks MP, the more answers the better.

 

Will you be fitting a cell compression case as mentioned in Dr Bobs last link, or are you confident that one is not required in your setup?

Edited by rusty69
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7 minutes ago, rusty69 said:

Good link Dr Bob (I have read it in the past iirc),The video of the chinamen abusing a set of cells gives me a bit more confidence should all these safety cut outs fail.

Thanks MP, the more answers the better.

 

Will you be fitting a cell compression case as mentioned in Dr Bobs last link, or are you confident that one is not required in your setup?

I have compression plates fitted. The arrangement I have is a set of six cells mechanically clamped together. The six cells are two sets of three in parallel, with the two sets in series to make a 6v "block". One of these blocks is roughly equivalent in size and weight to a 12v 110Ah lead-acid battery - about as much as you'd want to be lifting and moving in one go. I have two of the 6v blocks next to each other in the battery box, connected in series to form the final 12v battery.

 

The compression arrangement, which came as part of the deal on the cells, looks like factory parts. It consists of aluminium plates across the ends of the cells, joined by substantial  straps along the long sides of the cell stack.

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2 hours ago, Dr Bob said:

Thanks Simon.

If you have the time to do a hand drawn diagram that would be great. I've ordered the BEP motorised switch as per T&B's set up but interested to se how to wire the Tyco switch. Only do it if you have time.

On (3), OK. I guess if the LA bank is over 80% charged then it wont take that much current if the contactor to the Li bank is linked. I could therefore have a 12.5V lower limit set on the LA's BMV 712 to isolate the Lithium bank via the auto disconnect.

So that brings us back to (1) - can I control the auto disconnect switch (the BEP motorised switch) from 3 different devices (ie the 2 BMV 712s and the Australian BMS cell monitoring device)?

 

 

I'll try and put something down this evening.

 

On question 3), what are the outputs you're trying to combine. Active high or active low voltages, volt-free contacts, contact closures to ground?. Also what sort of signal does the BEP switch want?

 

MP.

 

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1 hour ago, MoominPapa said:

 

I'll try and put something down this evening.

 

On question 3), what are the outputs you're trying to combine. Active high or active low voltages, volt-free contacts, contact closures to ground?. Also what sort of signal does the BEP switch want?

 

MP.

 

I will have a few devices that have alarm and relay functions ie the BMV 712.  Each has a +ve and -ve connection to activate an external relay. For a normal relay, connect the coil to the connections with a 12v supply and when the alarm goes off the circuit closes so energises the coil. Can I parallel two or three 'activation' devices to just one relay?

I've ordered the BEP switch so I will work out what connection it wants when it arrives. The diagram on the info sheet on the net is not much help.

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