Cheap LiFePO4 BMS?

[MoominPapa]

50 minutes ago, ivan&alice said:

Quick question to those who have the Winston Thunderskys from Jeremy - what size bolts do the 160Ah cells take? The data sheet doesn't specify, Are they M8? (I'm shopping for lugs etc)

Mine came with bolts, so I'm absolutely sure, but I'd be surprised if they were anything other than M8. Certainly, lugs with 8mm dia. holes are the correct ones.

 

MP.

 

[Dr Bob]

21 minutes ago, MoominPapa said:

Mine came with bolts, so I'm absolutely sure, but I'd be surprised if they were anything other than M8. Certainly, lugs with 8mm dia. holes are the correct ones.

 

MP.

 

Yep, 8mm connectors on the cells but I got a pack of 10 of 8mm and 10 mm as various fuse holders, shunts etc can be 10mm.

[jetzi]

Thanks for this info. I want to try to consistently use 8mm as much as possible so I will always know that my insulated 13mm spanner is the one to grab. The only thing I have so far that isn't 8mm is the BMV shunt.

I have another question (or maybe just thinking out loud) - I want to add circuit breakers on each major subsystem so that I can isolate it for maintenance or in an emergency.

 

I'd like one between

• the alternator / battery+ (90A)
• inverter / battery+ (190A continuous, 500A surge)
• 12V DC fuse box / battery+ (50A)
• the MPPT / battery+ (100A)
• the MPPT / PV panels (10A @ 150V)
• global battery isolator on the battery negative

 

I'm using Tyco BDS-A 190A latching relays all over the system anyway. I could add push button switches for a manual override to turn them on/off, perhaps LEDs indicating their on/off state. I can picture a world where I can control this remotely which would be cool. Is there an issue with connecting multiple ways to turn off a relay? i.e. will the current from the button push interfere with the BMS? The biggest problem with this that I can see is that if the BMS or something decides to turn the thing back on? According to the Tyco BDS-A data sheet, they need a 15-100ms impulse to activate the coil. That sounds like a button press length, but would it be very bad if I pressed too long?

 

 

Another alternative is to use a DC circuit breakers in series with the each relay. Bimble have a circuit breaker that looks interesting to me, basically NH fuse holders with a lever allowing you to manually disconnect by pulling. Come in 2 pole versions as well. But 40 GBP each plus 6GBP for each fuse - not cheap!!!

 

 

Then there are lots of suspiciously cheap breakers on eBay which I think are meant for isolating car audio. Rated up to 300A so on paper they sound like they would do the job. But yeah - there must be a catch. And not a good catch like those in a latching relay.

[nicknorman]

Personally I’d avoid to many “things” in the high current circuits. Each one will drop some voltage, and each one gives reduced reliability.

 

I’d avoid one in the inverter circuit. In the unlikely event that you want to remove power from the inverter, just take the fuse out. I have done this once in 10 years, so the slight inconvenience was insignificant.

 

Same comment for between alternator and battery. Inadvertent operation may kill the alternator and it’s just another potential failure point.
 

The other ones seem more reasonable. Is 50A enough for your 12v cabin circuits? If you have a diesel heater (Mikuni/Webasto etc) they take around 25A whilst starting up, add in a fridge, lights, water pumps and you are getting close to 50A peak load.
 

On the tyco thing, I think it should be fine to parallel a push button across the BMS output, which will be a relay or open collector/open drain output. But to be sure, test it by measuring the voltage between the BMS output and both the 0v supply and the +12v supply, with the tyco disconnected. I would expect to get zero volts in both cases, showing the output is “floating” in its off state.
 

50-100ms is a pretty short dab of the button but I don’t think it will be that critical if it was say 200mS. If the button sticks down you have a problem though!

Edited May 23, 2020 by nicknorman

[peterboat]

Those circuit breakers from china are ok at Lower amps, but not much good really, you get what you pay for. I bought DC rated mcbs from an electrical company and have had one trip out. Prism solar who supplied my controller says that a lightning strike or near miss destroyed 3 fets and caused a short circuit, the mcb either tripped then or when the sun came up, this was just before lockdown and I will get the controller back next week 

[jetzi]

10 hours ago, nicknorman said:

I’d avoid one in the inverter circuit. In the unlikely event that you want to remove power from the inverter, just take the fuse out. I have done this once in 10 years, so the slight inconvenience was insignificant.

OK - the inverter I could leave permanently connected, because it has its own low voltage disconnect so that's fine I guess.

 

10 hours ago, nicknorman said:

Same comment for between alternator and battery. Inadvertent operation may kill the alternator and it’s just another potential failure point.

The alternator would still have the LA dump load so it wouldn't kill the alternator. I'm definitely having the breaker on the alternator input to the Li's, even if it's just the Tyco BDS-A controlled by the BMS.

 

10 hours ago, nicknorman said:

Personally I’d avoid to many “things” in the high current circuits. Each one will drop some voltage, and each one gives reduced reliability.

I would have thought that a switch would not count as a "thing" if it was rated correctly. Ok - I will avoid adding extra circuit breakers - then this lends weight to my idea to use only the relays (which are going to be there anyway) as circuit breakers with the push buttons for disconnects.

[nicknorman]

18 minutes ago, ivan&alice said:

OK - the inverter I could leave permanently connected, because it has its own low voltage disconnect so that's fine I guess.

 

The alternator would still have the LA dump load so it wouldn't kill the alternator. I'm definitely having the breaker on the alternator input to the Li's, even if it's just the Tyco BDS-A controlled by the BMS.

 

I would have thought that a switch would not count as a "thing" if it was rated correctly. Ok - I will avoid adding extra circuit breakers - then this lends weight to my idea to use only the relays (which are going to be there anyway) as circuit breakers with the push buttons for disconnects.

Yes obviously you need a disconnect between the alternator and the Li batteries, to protect the latter. I thought you were proposing a disconnect between the alternator and everything else, which I don’t think is necessary and has downsides.

 

A perfect switch of course doesn’t count as a “thing”, but they are hard to come by. Our boat had quality battery isolators but I noticed that when the alternator was charging hard (150A or so) it was getting warm and dropping 0.2v. I moved the alternator connection to the battery side of the isolator. We do get quite a few cases of people having electrical problems which turn out to be a high resistance connection in the isolator switch.

[jetzi]

Just now, nicknorman said:

Yes obviously you need a disconnect between the alternator and the Li batteries, to protect the latter. I thought you were proposing a disconnect between the alternator and everything else, which I don’t think is necessary and has downsides.

I wasn't clear, by "alternator" I meant the alternator side of the system, so alternator and starter battery permanently connected.

 

Is there anywhere that need a physical isolator switch on the lithium side? A master switch on the negative to isolate everything?

[TheBiscuits]

2 minutes ago, ivan&alice said:

Is there anywhere that need a physical isolator switch on the lithium side? A master switch on the negative to isolate everything?

Designed with a steel head and shaft this axe comes complete with an insulated handle that has been tested to 20,000V.  It meets BS3054.

 

 

 

[nicknorman]

5 minutes ago, ivan&alice said:

I wasn't clear, by "alternator" I meant the alternator side of the system, so alternator and starter battery permanently connected.

 

Is there anywhere that need a physical isolator switch on the lithium side? A master switch on the negative to isolate everything?

For the BSS you need to be able to isolate the batteries from the boat’s services (except for those services mentioned in the BSS checklist that are allowed to be permanently connected via a fuse). In this context I think we should take “the batteries” to mean all the batteries (LA and Li in parallel). Personally I’m not a fan of isolators in the -ve. Just have an isolator that disconnects the battery +ves from the boat’s services. You presumably have this already?

[jetzi]

Just now, nicknorman said:

For the BSS you need to be able to isolate the batteries from the boat’s services (except for those services mentioned in the BSS checklist that are allowed to be permanently connected via a fuse). In this context I think we should take “the batteries” to mean all the batteries (LA and Li in parallel). Personally I’m not a fan of isolators in the -ve. Just have an isolator that disconnects the battery +ves from the boat’s services. You presumably have this already?

Yes on my LA system there is an isolator on the negative. This becomes somewhat redundant when none of the boats services are going to be connected to the LA side - that circuit would just consist of a I'm thinking specifically about the new lithium system.

 

The lithium battery positive has four connections - two charge sources (alternator and MPPT) and two load sources (inverter and 12V fusebox). The alternator and 12V loads each need a tyco (BMS controlled disconnect, doubling as a breaker with manual pushbuttons). The inverter I will trust to low voltage disconnect itself, and the MPPT trust to high voltage disconnect. (I had been thinking of sticking a tyco and/or breaker in those two as well). I had also been planning a 250A fuse on each of those four positives.

 

The negative has the BMV shunt before going to the negative busbar connected to all of these.

 

So would the battery isolator then go on the positive before it splits into 4?

[nicknorman]

8 minutes ago, ivan&alice said:

Yes on my LA system there is an isolator on the negative. This becomes somewhat redundant when none of the boats services are going to be connected to the LA side - that circuit would just consist of a I'm thinking specifically about the new lithium system.

 

The lithium battery positive has four connections - two charge sources (alternator and MPPT) and two load sources (inverter and 12V fusebox). The alternator and 12V loads each need a tyco (BMS controlled disconnect, doubling as a breaker with manual pushbuttons). The inverter I will trust to low voltage disconnect itself, and the MPPT trust to high voltage disconnect. (I had been thinking of sticking a tyco and/or breaker in those two as well). I had also been planning a 250A fuse on each of those four positives.

 

The negative has the BMV shunt before going to the negative busbar connected to all of these.

 

So would the battery isolator then go on the positive before it splits into 4?

Yes it could do, that would be BSS compliant. Of the 4 things you mention only the MPPT doesn’t require an isolator (just a fuse) - that is, presuming the inverter is just an inverter and not a Combi? A Combi can also be wired direct to the battery via a fuse. So you could have the MPPT wired direct, the alternator and 50A services via the isolator, and the inverter one or other of those depending on whether it’s an inverter or a Combi. But it might be easier simply to have the lot going through the isolator.

 

ps the LA battery isolator isn’t redundant - you need (for BSS purposes) to be able to isolate the battery from everything (except those ive mentioned above) and that includes being isolated from the alternator.

Edited May 23, 2020 by nicknorman

[jetzi]

Just now, nicknorman said:

Yes it could do, that would be BSS compliant. Of the 4 things you mention only the MPPT doesn’t require an isolator (just a fuse) - that is, presuming the inverter is just an inverter and not a Combi? A Combi can also be wired direct to the battery via a fuse. So you could have the MPPT wired direct, the alternator and 50A services via the isolator, and the inverter one or other of those depending on whether it’s an inverter or a Combi. But it might be easier simply to have the lot going through the isolator.

It is just an inverter (Victron Phoenix 3000kVA) so it would need to be behind the isolator. Certainly sounds easier to just have the lot go through the isolator. What advantage is there not including the MPPT? If I had a breaker on the PV panels then I could flip that before switching the isolator.

[WotEver]

Interesting video here where a guy makes a portable 3.5kWh power pack for about $600 US from bare cells. I thought it was pretty cool. 

 

[jetzi]

14 hours ago, nicknorman said:

ps the LA battery isolator isn’t redundant - you need (for BSS purposes) to be able to isolate the battery from everything (except those ive mentioned above) and that includes being isolated from the alternator.

Thanks for pointing this out, I would not have expected BSS to require isolating LA from the alternator. I will leave the current isolator in place - this will only be isolating the starter motor and alternators from the LA. I will add a new isolator on the positive of the Li's isolating everything (including MPPT - I will put up a label reminding me to trip the breaker on the PV before isolating the Li positive to prevent damage to my MPPT).

 

Regarding this new isolator, would it make sense to put a double pole isolator and isolate both positive and negative at the same time (i.e. completely isolate the whole Li battery bank)? There seems to be (as always) a huge range in prices on these things and I'm not sure if you always "get what you pay for" or if some of them are cheapos that have just been marked up to look like good quality ones.

Edited May 24, 2020 by ivan&alice

[Dr Bob]

2 hours ago, WotEver said:

Interesting video here where a guy makes a portable 3.5kWh power pack for about $600 US from bare cells. I thought it was pretty cool. 

 

Yes, interesting video. All those small batteries! Just like my Tesla! 

Now the BMS was only 60A ...but at 48V. So all the boaters needing 200A+ for a boat 12V system...it's different. Does that point us in the direction of higher voltage for a simpler BMS?

[WotEver]

26 minutes ago, Dr Bob said:

Yes, interesting video. All those small batteries! Just like my Tesla! 

Now the BMS was only 60A ...but at 48V. So all the boaters needing 200A+ for a boat 12V system...it's different. Does that point us in the direction of higher voltage for a simpler BMS?

It could, but a 48V to 12V @ 200A buck converter would be pretty pricey.

[jetzi]

34 minutes ago, WotEver said:

It could, but a 48V to 12V @ 200A buck converter would be pretty pricey.

Why not run boats at 48V? (for me it's the fact that I already have a ton of 12V equipment - but if starting from scratch it seems like that might be a better idea - provided you can get 12V water/shower/etc pumps)

[WotEver]

27 minutes ago, ivan&alice said:

Why not run boats at 48V? (for me it's the fact that I already have a ton of 12V equipment - but if starting from scratch it seems like that might be a better idea - provided you can get 12V water/shower/etc pumps)

Simply the availability of 48V kit.

[TheBiscuits]

5 minutes ago, WotEver said:

Simply the availability of 48V kit.

48V inverters are common enough, and if you have several kWh of batteries you can just run everything on mains - or even run the mains charger for your 12V battery bank!

[WotEver]

20 minutes ago, TheBiscuits said:

48V inverters are common enough, and if you have several kWh of batteries you can just run everything on mains

Yup, good point

[nicknorman]

22 hours ago, ivan&alice said:

It is just an inverter (Victron Phoenix 3000kVA) so it would need to be behind the isolator. Certainly sounds easier to just have the lot go through the isolator. What advantage is there not including the MPPT? If I had a breaker on the PV panels then I could flip that before switching the isolator.

The advantage of not including the MPPT is that some folk like to open their battery isolator when they leave the boat, to ensure they haven’t left anything on and I suppose for a slight element of safety (everything is disconnected). But by leaving the MPPT connected it means the batteries continue to be charged / kept topped up by the solar. Also eliminates the risk of damage to the MPPT from disconnecting the batteries when the MPPT is producing current.

8 hours ago, ivan&alice said:

Thanks for pointing this out, I would not have expected BSS to require isolating LA from the alternator. I will leave the current isolator in place - this will only be isolating the starter motor and alternators from the LA. I will add a new isolator on the positive of the Li's isolating everything (including MPPT - I will put up a label reminding me to trip the breaker on the PV before isolating the Li positive to prevent damage to my MPPT).

 

Regarding this new isolator, would it make sense to put a double pole isolator and isolate both positive and negative at the same time (i.e. completely isolate the whole Li battery bank)? There seems to be (as always) a huge range in prices on these things and I'm not sure if you always "get what you pay for" or if some of them are cheapos that have just been marked up to look like good quality ones.

I don’t see any advantage is a double pole isolator - each pole represents potential voltage drop and unreliability, so you have doubled both those!

[jetzi]

1 hour ago, nicknorman said:

The advantage of not including the MPPT is that some folk like to open their battery isolator when they leave the boat, to ensure they haven’t left anything on and I suppose for a slight element of safety (everything is disconnected). But by leaving the MPPT connected it means the batteries continue to be charged / kept topped up by the solar. Also eliminates the risk of damage to the MPPT from disconnecting the batteries when the MPPT is producing current.

I don’t see any advantage is a double pole isolator - each pole represents potential voltage drop and unreliability, so you have doubled both those!

As liveaboard CCers we never leave our boat for more than a couple of nights. Regarding the risk of damage to the MPPT - I'm putting a 100A/250V DC breaker for the PV right next to the isolator with a big sign saying "don't isolate without tripping PV breaker" - hopefully this will sufficiently muppetproof it. All this talk of voltage drop and unreliability persuaded me not to cheap out - I got a 300A rated Blue Sea Systems isolator for 33 GBP which will be the first and only thing on the Li positive, and the momentary push switches to manually open/close the Tyco relays on each subsystem to act as breakers.

 

I've ordered all the bits, just counting down the days until we're running on Lithium!! Very excited - will definitely report back here with how the build went and how it's working.

[peterboat]

6 minutes ago, ivan&alice said:

As liveaboard CCers we never leave our boat for more than a couple of nights. Regarding the risk of damage to the MPPT - I'm putting a 100A/250V DC breaker for the PV right next to the isolator with a big sign saying "don't isolate without tripping PV breaker" - hopefully this will sufficiently muppetproof it. All this talk of voltage drop and unreliability persuaded me not to cheap out - I got a 300A rated Blue Sea Systems isolator for 33 GBP which will be the first and only thing on the Li positive, and the momentary push switches to manually open/close the Tyco relays on each subsystem to act as breakers.

 

I've ordered all the bits, just counting down the days until we're running on Lithium!! Very excited - will definitely report back here with how the build went and how it's working.

That breaker is a bit large! 

[nicknorman]

11 hours ago, ivan&alice said:

...and the momentary push switches to manually open/close the Tyco relays on each subsystem to act as breakers.

Bear in mind that the relay coil takes about 3A DC so you need push switches that can cope with that current. The last thing you want is for the contacts to weld themselves closed! I also notice that the Tyco has built in freewheel diodes which is great for protecting the buttons, but it also means each coil is polarity sensitive. If you get + and - the wrong way round, something will melt!