Cheap LiFePO4 BMS?

[Dr Bob]

18 hours ago, ivan&alice said:

 

Here's a real newbie question: would it be sensible to get to 100% every few months (straight after balancing) to check on capacity and erase any "memory effect"? Of course, discharging the batteries promptly thereafter and not storing them at 100% even overnight.

 

 

I agree with Tom above saying that getting back to 100% is to re-sync the battery monitor...and I do this every 2-3months .....but tend to just follow voltage as the Ahrs used does get a bit out of kilter with the actual Ahrs used.

The 'memory' effect though is a more difficult question. Is there a 'memory effect'? I've not a clue....but there is a lot of peeps with boats who think there is. If you start looking at this thread on the US dominated cruiser forum

https://www.cruisersforum.com/forums/f166/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069.html

you will see lots of references to it. This thread has been going 8 years so there is a tad more experience than on our forum (references to memory effect are in the last year). I think it also spawned a separate thread on the memory effect which I read  6 months ago but then lost interest. The 'Marine how to site' also talks about its as does the Nordkyn site. Myself (after 12 months experience), I have not seen any evidence of a memory effect - although I am taking mine to 98% every 2-3 months - but then I am not sure I would see a memory effect as I have not done any real capacity testing. I didnt check the capacity when I got the cells so nothing to compare to. The voltage at rest vs Ahrs used graph hasnt changed in 12 months so I am thinking not much has changed.

As far as I could tell when I last looked at the cruiser forum, you can negate the memory effect by taking it to 100% a few times a year.......so by re-syncing the meter, you are avoiding the memory problem....if it exists.

There's not enough of us using Li's on here to see if there is a problem here.

[nicknorman]

34 minutes ago, Mike the Boilerman said:

 

Thanks for the link.

 

And yes even I understand power factor and the phase angle between current and voltage. When the phase angle reaches 90 degrees then the power falls to zero IIRC even though the VA remains up at whatever it was to start with. Not that this ever happens in real life but if it did, where does the energy go?

 

 

 

 

The energy doesn’t go anywhere, in theory. And yes it can happen, consider a capacitor connected across the mains. The current and voltage waveforms are (theoretically) 90 deg out of phase and so the power dissipated by the capacitor is zero. Replace the capacitor with a resistor of a value to give the same current, and the voltage and current are now in phase, so lots of resistor-frying power is dissipated.

 

or consider a resonant circuit comparing an inductor and capacitor in parallel. Once you put energy in by way of alternating current at the resonant frequency into the circuit, that energy continues to circulate (theoretically) indefinitely and is not dissipated.

 

I say “theoretically” in the above examples, because in reality a device like a capacitor does have some resistance and so the current will generate some ohmic heating / wasted power. And this is why electric companies don’t like loads with power factor away from unity - it creates a lot of pointless current circulating in the distribution lines that, due to their resistance, causes power loss from ohmic heating for no benefit.

Edited April 3, 2020 by nicknorman

[MtB]

11 minutes ago, nicknorman said:

The energy doesn’t go anywhere, in theory. And yes it can happen, consider a capacitor connected across the mains. The current and voltage waveforms are (theoretically) 90 deg out of phase and so the power dissipated by the capacitor is zero. Replace the capacitor with a resistor of a value to give the same current, and the voltage and current are now in phase, so lots of resistor-frying power is dissipated.

 

or consider a resonant circuit comparing an inductor and capacitor in parallel. Once you put energy in by way of alternating current at the resonant frequency into the circuit, that energy continues to circulate (theoretically) indefinitely and is not dissipated.

 

I say “theoretically” in the above examples, because in reality a device like a capacitor does have some resistance and so the current will generate some ohmic heating / wasted power. And this is why electric companies don’t like loads with power factor away from unity - it creates a lot of pointless current circulating in the distribution lines that, due to their resistance, causes power loss from ohmic heating for no benefit.

 

Thanks Nick. I think I get all that. 

 

I notice I sort of answered my own question too, in the way I constructed it. 

 

"When the phase angle reaches 90 degrees then the power falls to zero"

[WotEver]

And this is why electricity companies would love to charge you by kVAh instead of kWh, but they’re not allowed

[MoominPapa]

14 minutes ago, nicknorman said:

The energy doesn’t go anywhere, in theory. And yes it can happen, consider a capacitor connected across the mains. The current and voltage waveforms are (theoretically) 90 deg out of phase and so the power dissipated by the capacitor is zero. Replace the capacitor with a resistor of a value to give the same current, and the voltage and current are now in phase, so lots of resistor-frying power is dissipated.

 

or consider a resonant circuit comparing an inductor and capacitor in parallel. Once you put energy in by way of alternating current at the resonant frequency into the circuit, that energy continues to circulate (theoretically) indefinitely and is not dissipated.

 

I say “theoretically” in the above examples, because in reality a device like a capacitor does have some resistance and so the current will generate some ohmic heating / wasted power. And this is why electric companies don’t like loads with power factor away from unity - it creates a lot of pointless current circulating in the distribution lines that, due to their resistance, causes power loss from ohmic heating for no benefit.

I have a little device to defeat the power saving mode on the inverter which consists of a 1uF X2 capacitor and a switch across the mains. Close the switch and the reactive power is enough to make the inverter think it has a load and switch to inverting mode, but there's no problem wasting energy or having to dissipate the heat involved in with 10 or 20 watts of real power. 

 

MP.

 

[WotEver]

4 minutes ago, MoominPapa said:

I have a little device to defeat the power saving mode on the inverter which consists of a 1uF X2 capacitor and a switch across the mains. Close the switch and the reactive power is enough to make the inverter think it has a load and switch to inverting mode, but there's no problem wasting energy or having to dissipate the heat involved in with 10 or 20 watts of real power. 

 

MP.

 

Neat

[nicknorman]

19 minutes ago, Mike the Boilerman said:

 

Thanks Nick. I think I get all that. 

 

I notice I sort of answered my own question too, in the way I constructed it. 

 

"When the phase angle reaches 90 degrees then the power falls to zero"

Yes, the principle of conservation of energy answers a lot of questions!

[TheBiscuits]

16 minutes ago, MoominPapa said:

I have a little device to defeat the power saving mode on the inverter which consists of a 1uF X2 capacitor and a switch across the mains. Close the switch and the reactive power is enough to make the inverter think it has a load and switch to inverting mode, but there's no problem wasting energy or having to dissipate the heat involved in with 10 or 20 watts of real power. 

 

It's a nice hack, but surely your inverter power usage increases when your switch is on.

 

If the inverter doesn't use any more power in working mode than in power saving mode, why not simply disable power saving mode?

 

 

 

[MoominPapa]

1 hour ago, TheBiscuits said:

 

It's a nice hack, but surely your inverter power usage increases when your switch is on.

 

If the inverter doesn't use any more power in working mode than in power saving mode, why not simply disable power saving mode?

It does increase power consumption when the inverter comes out of power saving mode, but not by any more than that, the hack doesn't add to the power use.  The hack gets turned on when we're using low power devices like chargers and soldering irons, or stuff like drills where a 0-1 second delay after you press the trigger is annoying and dangerous.

 

The reason for using this hack rather than switching the inverter power saving mode is to change the power saving mode on this particular inverter you have to 1) turn it off, 2) turn it on again and wait until the display says "power save on". 3) turn if off again, 4) turn it on again, when it comes up in power save off mode. If you get the timing of this wrong you tickle a firmware bug and when it comes on the second time it cycles between the two modes every second forever and the only way to reset it is to isolate the batteries for a few seconds. Flicking a switch which has a warning light to remind you to switch it off when you've finished is much more satisfactory.

 

MP.

 

 

[TheBiscuits]

4 minutes ago, MoominPapa said:

The reason for using this hack rather than switching the inverter power saving mode is to change the power saving mode on this particular inverter you have to 1) turn it off, 2) turn it on again and wait until the display says "power save on". 3) turn if off again, 4) turn it on again, when it comes up in power save off mode. If you get the timing of this wrong you tickle a firmware bug and when it comes on the second time it cycles between the two modes every second forever and the only way to reset it is to isolate the batteries for a few seconds. Flicking a switch which has a warning light to remind you to switch it off when you've finished is much more satisfactory.

 

Ah.  I can see why you added the switch!  All the ones I have faffed with have either a dipswitch or a software setting that lets you turn off stupid mode.

 

I have never had to resort to sending pulse codes with the on/off switch! 

 

[jetzi]

4 hours ago, Tom and Bex said:

I find when charging at 70-90A via alternator, then with our setup, the batteries are around 80-85% charged when the voltage hits 14.0v, and if we want to charge them higher, we continue in constant voltage mode.

Am I to understand that you're able to modify the voltage output of your alternator?

 

4 hours ago, Tom and Bex said:

with 3 cells in series then you're looking at limit of 600A! Even with big inverter I doubt you'd be able to get near that!

4 in series = 800A? (to get up to 12V - with each 3.2V cell being 3 cells in parallel?)

 

If I got the 3kVA inverter, that would be 2400W using Peter's 80% rule and 240A using Nick's 10V rule for losses. I can check with Jeremy if he means 200A per cell or per battery.

 

What would happen if I tried to pull more than 200A out of the batteries, would something bad happen? Would the inverter just dip the voltage too low and crash the system?

 

4 hours ago, Tom and Bex said:

Only real reason to get to 100% is to re-sync battery monitor. What monitoring are you planning for soc? Does the bms give this info?

Oh dear. Monitoring is an aspect I seem to have overlooked!! I thought I'd be able to integrate it with the Victron monitoring (MPPT and inverter) somehow, but I haven't given proper thought to this. The instructions of the BMS say:

Quote

For various display and communications modules, such as a digital voltmeter, Arduino and Raspberry microcomputers, LAN Controller by Tinycontrol, Siemens LOGO PLCs, Schneider Zelio PLC module, Eaton Easy PLC, TECO Foxtrott PLC, etc.

Most of that nothing to me. I'm a software engineer by trade what I might do in the medium term is write my own interface and run it on a Raspberry Pi or something. Do you have any recommendations on monitoring?

 

4 hours ago, Tom and Bex said:

We use our washing machine quite happily off our 1500w inverter and it doesn't get near the limit. Ours has control to set wash temperature that overrides program setting - we leave this permanently set to cold, and have it connected via mixer valve so it fills with hot water for the wash, and we switch mixer valve back to cold for rinses (if we remember!)

I've sited the washing machine next to the cauliflower for this reason - well insulated pipes will feed the machine with hot water as needed. Washing machine has a "cold wash" button that completely disables the heater rather than simply setting to 30 degrees. The mixer tap next to the machine will then be like the "temperature dial" on your fully automatic. And will keep the same temperature for the whole cycle - rinses as well as washes. Old fashioned I know but I'm a big believer in hot water for cleaning everything.

 

4 hours ago, peterboat said:

I would have liked a hot water fill type washer but they are expensive 

Just put the hot water into the cold filler

 

4 hours ago, Tom and Bex said:

I think in reality you're unlikely to get through many 200A fuses. Don't forget fuses won't blow the moment you exceed 200A, depending on the fuse you will probably have to exceed 200A by quite a bit or for some time before it blows. We have 150A fuse, and not blown it yet, even starting engine from our lithium batteries several times when the starter battery failed. 

This is good to know, thanks. If I go for a 3kVA inverter I'll get a 250A fuse, and if 2kVA I'll get a 200A fuse.

 

4 hours ago, Tom and Bex said:

I don't think you need an additional low voltage cut off. The bms should provide that based on cell voltage, not sure much benefit to be gained by having an additional cut off based on system voltage. 

 

I do like the look of that bms so will be interested to hear how you get on with it. 

I'm excited to report back, so I'll definitely supply a full review in a couple of months! The system voltage cutoff idea is really just a belt and braces thing, but yes I can just rely on the BMS. I do plan on getting four really cheap low voltage buzzers to put on each cell just in case the BMS doesn't work. Would love to have high-voltage buzzers too, but couldn't find those with a cursory look on Amazon.

 

 

 

3 hours ago, Dr Bob said:

I agree with Tom above saying that getting back to 100% is to re-sync the battery monitor...and I do this every 2-3months .....but tend to just follow voltage as the Ahrs used does get a bit out of kilter with the actual Ahrs used.

Not just for the SoC monitor, but initially I want to rebalance my cells manually every 2-3 months just to see how they are working. Whether I choose to top balance or bottom balance, I still plan to check the other (top or bottom) to help inform whether 80/20 is a reasonable rule in my case. If I top balance, I think it would make sense to follow something like 85/20 or 90/25 and if I bottom balance 80/15 or 75/10. Initially though I will be extremely conservative - 70/30 rather than 80/20!

 

So yes - no memory effect for me, even if it is a real thing.

 

38 minutes ago, MoominPapa said:

The reason for using this hack rather than switching the inverter power saving mode is to change the power saving mode on this particular inverter you have to 1) turn it off, 2) turn it on again and wait until the display says "power save on". 3) turn if off again, 4) turn it on again, when it comes up in power save off mode. If you get the timing of this wrong you tickle a firmware bug and when it comes on the second time it cycles between the two modes every second forever and the only way to reset it is to isolate the batteries for a few seconds. Flicking a switch which has a warning light to remind you to switch it off when you've finished is much more satisfactory.

Very clever, thanks for the explanation!

 

---

 

So, I had a look at my options for a dishwasher. Consider this one:

 

https://www.currys.co.uk/gbuk/household-appliances/dishwashing/dishwashers/zanussi-zdm17301wa-compact-dishwasher-white-10154246-pdt.html

 

They never seem to want to give you a straight answer with wattage, but it says 0.61kW per cycle and 55 mins per cycle, which suggests 660W or so average. Even if it's double this during heating, say, (1320W) the 2kVA / 1600W Victron Smart inverter I was originally keen on still appears to be enough to run it. Ilike the idea of limiting my outgoing current to 200A, so I'm leaning back towards the 2kVA inverter.

 

Can anyone think what else I might want to power one day off that inverter that I should think about? How much power does an electric welding machine use?

Edited April 3, 2020 by ivan&alice

[Richard10002]

16 hours ago, ivan&alice said:

Hi Richard, sorry to worry you.

............

16 hours ago, ivan&alice said:

Sorry I don't have a definitive reason why you shouldn't use a battery protect with an inverter for at the moment, but I don't think your setup is posing you imminent danger! I'll look tomorrow if none of the electronics big guns on the forum have an explanation.

 

No problem... My inverter/charger is currently connected to my LA bank, which is completely separate to my Lithium bank, so no danger whatsoever right now

 

I have been thinking about switching to using the lithiums to power the inverter.. I'll pop that on hold for now until something definitive pops up.

 

Thanks for the heads up  

 

 

[peterboat]

7 minutes ago, ivan&alice said:

Am I to understand that you're able to modify the voltage output of your alternator?

 

4 in series = 800A? (to get up to 12V - with each 3.2V cell being 3 cells in parallel?)

 

If I got the 3kVA inverter, that would be 2400W using Peter's 80% rule and 240A using Nick's 10V rule for losses. I can check with Jeremy if he means 200A per cell or per battery.

 

What would happen if I tried to pull more than 200A out of the batteries, would something bad happen? Would the inverter just dip the voltage too low and crash the system?

 

Oh dear. Monitoring is an aspect I seem to have overlooked!! I thought I'd be able to integrate it with the Victron monitoring (MPPT and inverter) somehow, but I haven't given proper thought to this. The instructions of the BMS say:

Most of that nothing to me. I'm a software engineer by trade what I might do in the medium term is write my own interface and run it on a Raspberry Pi or something. Do you have any recommendations on monitoring?

 

I've sited the washing machine next to the cauliflower for this reason - well insulated pipes will feed the machine with hot water as needed. Washing machine has a "cold wash" button that completely disables the heater rather than simply setting to 30 degrees. The mixer tap next to the machine will then be like the "temperature dial" on your fully automatic. And will keep the same temperature for the whole cycle - rinses as well as washes. Old fashioned I know but I'm a big believer in hot water for cleaning everything.

 

Just put the hot water into the cold filler

 

This is good to know, thanks. If I go for a 3kVA inverter I'll get a 250A fuse, and if 2kVA I'll get a 200A fuse.

 

I'm excited to report back, so I'll definitely supply a full review in a couple of months! The system voltage cutoff idea is really just a belt and braces thing, but yes I can just rely on the BMS. I do plan on getting four really cheap low voltage buzzers to put on each cell just in case the BMS doesn't work. Would love to have high-voltage buzzers too, but couldn't find those with a cursory look on Amazon.

 

 

 

Not just for the SoC monitor, but initially I want to rebalance my cells manually every 2-3 months just to see how they are working. Whether I choose to top balance or bottom balance, I still plan to check the other (top or bottom) to help inform whether 80/20 is a reasonable rule in my case. If I top balance, I think it would make sense to follow something like 85/20 or 90/25 and if I bottom balance 80/15 or 75/10. Initially though I will be extremely conservative - 70/30 rather than 80/20!

 

So yes - no memory effect for me, even if it is a real thing.

 

Very clever, thanks for the explanation!

 

---

 

So, I had a look at my options for a dishwasher. Consider this one:

 

https://www.currys.co.uk/gbuk/household-appliances/dishwashing/dishwashers/zanussi-zdm17301wa-compact-dishwasher-white-10154246-pdt.html

 

They never seem to want to give you a straight answer with wattage, but it says 0.61kW per cycle and 55 mins per cycle, which suggests 660W or so average. Even if it's double this during heating, say, (1320W) the 2kVA / 1600W Victron Smart inverter I was originally keen on still appears to be enough to run it. Ilike the idea of limiting my outgoing current to 200A, so I'm leaning back towards the 2kVA inverter.

 

Can anyone think what else I might want to power one day off that inverter that I should think about? How much power does an electric welding machine use?

The electric welder tripped out my 2.4 KW victron inverter quite quickly I am afraid, I borrowed my mates Honda engined one, the engine was rated at 10 hp which is 12500 watts but thats for welding very thick steel

 

The reason why I dont put hot into the cold water fill is when I did it on my last boat it left the clothes very creased and a bugger to iron

Edited April 3, 2020 by peterboat

[jetzi]

6 minutes ago, Richard10002 said:

No problem... My inverter/charger is currently connected to my LA bank, which is completely separate to my Lithium bank, so no danger whatsoever right now

 

I have been thinking about switching to using the lithiums to power the inverter.. I'll pop that on hold for now until something definitive pops up.

What inverter do you have? Can you set a low voltage shutoff for it? If so, why not use the battery protect for your 12V loads and just power it directly from the batteries?

 

I guess it's because your BMS will shut down the battery protect if one cell falls low enough, whereas the inverter will only look at the whole battery?

 

I know you probably did say somewhere, but what BMS are you using - if you can control a bistable relay with it, I found a blinder of a deal on them on eBay:

 

https://www.ebay.co.uk/itm/Tyco-BDS-A-V23130-C2021-A412-12V-190A-KFZ-Bistable-Car-Relay-Switch-Ford-FoMoCo/254552588268

 

Would 190A be enough for your inverter?

 

8 minutes ago, peterboat said:

The electric welder tripped out my 2.4 KW victron inverter quite quickly I am afraid

And you can't get a smaller welder?

 

8 minutes ago, peterboat said:

he reason why I dont put hot into the cold water fill is when I did it on my last boat it left the clothes very creased and a bugger to iron

I have heard that rinsing in hot water can cause creases. Oh well, might have to have a semi-automatic washing machine, where I manually turn the tap to cold for the rinse. Will see how it goes.

[WotEver]

6 hours ago, nicknorman said:

It occurs to me that certainly for boating use, all heavy mains consumers are virtually pure resistive loads...

What about the charger?  Oh, wait...

[Richard10002]

1 hour ago, ivan&alice said:

What inverter do you have? Can you set a low voltage shutoff for it? If so, why not use the battery protect for your 12V loads and just power it directly from the batteries?

Sterling Pro Combi S 2500W Inverter Charger. It may have an inbuilt low voltage shut off around 10V, but it matters not as its a combi  

 

My mind says I could connect it so that the inverter charger enters the circuit between batteries and Battery Protect, but that would seem to defeat the object of the Battery Protect and, presumably, any surge from the inverter would still reach it.

1 hour ago, ivan&alice said:

 

I know you probably did say somewhere, but what BMS are you using - if you can control a bistable relay with it, I found a blinder of a deal on them on eBay:

 

https://www.ebay.co.uk/itm/Tyco-BDS-A-V23130-C2021-A412-12V-190A-KFZ-Bistable-Car-Relay-Switch-Ford-FoMoCo/254552588268

 

No BMS. I'm using Valence 12V batteries, same as Peter, (boat).

 

I do have a Victron BMV 712 Smart Monitor, which can control a relay, but I was planning to use it to control a relay in the charging part of the circuit, to protect against high voltage. It also has a low voltage function but I don't think it can control 2 different relays. (need to have a look at the manual as it was pretty much fit and forget).

 

I think I'm more worried about low voltage damage than high voltage damage, so I could switch my intentions regarding the relay to low voltage protection.

 

I don't really know what a bi stable relay does, nor how it would work in this application? Notwithstanding that, 2500W/13V = 193A, so 190A would almost certainly be fine.

[jetzi]

2 hours ago, Richard10002 said:

It may have an inbuilt low voltage shut off around 10V

Ah I think I understand. You dont have a BMS, so are relying on the battery protect to shut off the batteries at the voltage representing 20% (or whatever) SoC. I presume you set the cutoff voltage on the battery protect higher than 10V as i guess that would probably be too low for your batteries?

 

2 hours ago, Richard10002 said:

Victron BMV 712 Smart Monitor, which can control a relay, but I was planning to use it to control a relay in the charging part of the circuit, to protect against high voltage. It also has a low voltage function but I don't think it can control 2 different relays.

OK so at the moment the BMV is just for monitoring, but you are going to use it to shut off charging (from alternator I presume).

 

2 hours ago, Richard10002 said:

I don't really know what a bi stable relay does, nor how it would work in this application? Notwithstanding that, 2500W/13V = 193A, so 190A would almost certainly be fine.

It is just a relay like what you need for cutting off the high voltage, but unlike a standard relay takes no power to "hold" its position either on or off. I saw it as an alternative to the battery protect (which uses solid state MOSFET transistors instead of a physical switch). You might still wish to get one for cutting off the charge at high voltage signalled by the BMV. Or get two. One for high voltage controlled by the BMV and a second, as well as a second voltage monitor, that can handle your low voltage situation.

 

Seems reasonable to me but I'm a newbie and like to hear from someone like @MoominPapa @Dr Bob

 @nicknorman - is it possible to have a pair of voltage monitors each controlling its own relay, one to turn off charging at high voltage and one to turn off load at low voltage?

[Dr Bob]

41 minutes ago, ivan&alice said:

Ah I think I understand. You dont have a BMS, so are relying on the battery protect to shut off the batteries at the voltage representing 20% (or whatever) SoC. I presume you set the cutoff voltage on the battery protect higher than 10V as i guess that would probably be too low for your batteries?

 

OK so at the moment the BMV is just for monitoring, but you are going to use it to shut off charging (from alternator I presume).

 

It is just a relay like what you need for cutting off the high voltage, but unlike a standard relay takes no power to "hold" its position either on or off. I saw it as an alternative to the battery protect (which uses solid state MOSFET transistors instead of a physical switch). You might still wish to get one for cutting off the charge at high voltage signalled by the BMV. Or get two. One for high voltage controlled by the BMV and a second, as well as a second voltage monitor, that can handle your low voltage situation.

 

Seems reasonable to me but I'm a newbie and like to hear from someone like @MoominPapa @Dr Bob

 @nicknorman - is it possible to have a pair of voltage monitors each controlling its own relay, one to turn off charging at high voltage and one to turn off load at low voltage?

I use the BMV which you can set to activate a relay that switches when conditions of high voltage, low voltage, high SoC and high and low temp occur. If any of these inputs are triggered then the BMV switches the relay....either on or off......But it doesn't work with latching relay. You need to build a small circuit to go between the BMV relay and the tyco. @MoominPapa and nick both have proposed suitable circuits. Me being a muppet took the easy way out and spent the cash on a BEP motorised switch like Tom. There are commercial units that will interface to switch a latching relay.

Yes you could use a pair of voltage monitors but again make sure they activate the latching relay.

 

 

 

 

....eta, just noticed you need two relays, one for charging and one for loads. That's what Tom uses. a

A BEP switch for one and a tyco for the other. A BMV wouldn't work to activate both as if the voltage went low, the BMV would disconnect both charge and load. All you need to do is use the BMV for high voltage disconnect on the charge side and a cheap Amazon voltage board (£10 ish) for the low voltage disconnect on the load side.

I find my set up though works fine with just one auto disconnect on both charge and load. It never goes that low and lights bleep and alarms sound if it did...and then I disconnect and use the LAs. You are having some LAs in circuit?? Very useful.

Edited April 3, 2020 by Dr Bob

[peterboat]

1 hour ago, ivan&alice said:

Ah I think I understand. You dont have a BMS, so are relying on the battery protect to shut off the batteries at the voltage representing 20% (or whatever) SoC. I presume you set the cutoff voltage on the battery protect higher than 10V as i guess that would probably be too low for your batteries?

 

 

Hi Ivan, Valence batteries come with an internal BMS and the batteries can interconnect to talk to each other, I have 6 for leisure, 30 x 36 volt for drive and another 4 on my electric truck, you can chat to them on your puter to see what they are doing. They are the dogs do dahs, the 12 Volt version I have been using for coming up to 3 years with no issues. I have to say I very rarely check them as they are always balanced

[jetzi]

9 hours ago, Dr Bob said:

I use the BMV which you can set to activate a relay that switches when conditions of high voltage, low voltage, high SoC and high and low temp occur. If any of these inputs are triggered then the BMV switches the relay....either on or off......But it doesn't work with latching relay. You need to build a small circuit to go between the BMV relay and the tyco. @MoominPapa and nick both have proposed suitable circuits. Me being a muppet took the easy way out and spent the cash on a BEP motorised switch like Tom. There are commercial units that will interface to switch a latching relay.

Yes you could use a pair of voltage monitors but again make sure they activate the latching relay.

@Richard ah so apparently the BMV won't trigger a latching relay, sorry - the link I sent won't help you by itself.

 

 

9 hours ago, Dr Bob said:

just noticed you need two relays, one for charging and one for loads. That's what Tom uses. a

A BEP switch for one and a tyco for the other. A BMV wouldn't work to activate both as if the voltage went low, the BMV would disconnect both charge and load. All you need to do is use the BMV for high voltage disconnect on the charge side and a cheap Amazon voltage board (£10 ish) for the low voltage disconnect on the load side.

I find my set up though works fine with just one auto disconnect on both charge and load. It never goes that low and lights bleep and alarms sound if it did...and then I disconnect and use the LAs. You are having some LAs in circuit?? Very useful.

Sorry I may have confused things by starting to talk about Richards system. Mine is going to be quite different. For one, I don't have a BMV. I'll only set high and low voltage cutoffs on my BMS and hook them up to 2 separate Tyco relays. Does mean I will have no idea how many ants are in my batteries.

 

I mentioned that I'm planning not to connect the alternator at first, so on the charge side, I would use the MPPT's voltage cutoff to switch to float (i.e. off). This would happen on high voltage OR on low temperature. On the load side I'd use the GWL BMS board hooked up to a Tyco 190A relay.

When I connect the alternator, I will parallelise the LAs and use a second Tyco relay to isolate the Li's. The GWL BMS can connect up to 3 latching relays! The third opens when 0.3V higher or lower than the min/max values you set - I'll use this for an alarm I think. But yes, the charge-isolating relay will isolate the Li's from the LAs.

 

8 hours ago, peterboat said:

Valence batteries come with an internal BMS and the batteries can interconnect to talk to each other

I know, but that's not what we were asking. I wanted to know if Richard could drive a load-disconnect relay to replace his Victron Battery Protect that's between his battery and inverter - can you connect a load-disconnect relay to the Valence internal BMS to trigger on low voltage? I'm guessing not. But @Dr Bob does mention that you can get "a cheap Amazon voltage board (£10 ish) for the low voltage disconnect on the load side."

 

I found this: https://www.amazon.co.uk/KKmoon-Voltage-Detection-Charging-Discharge/dp/B019YWUI5G but it doesn't look like you can connect a latching relay, only a powered one. Any idea what to search for?

[Dr Bob]

19 minutes ago, ivan&alice said:

@Richard ah so apparently the BMV won't trigger a latching relay, sorry - the link I sent won't help you by itself.

 

 

Sorry I may have confused things by starting to talk about Richards system. Mine is going to be quite different. For one, I don't have a BMV. I'll only set high and low voltage cutoffs on my BMS and hook them up to 2 separate Tyco relays. Does mean I will have no idea how many ants are in my batteries.

 

I mentioned that I'm planning not to connect the alternator at first, so on the charge side, I would use the MPPT's voltage cutoff to switch to float (i.e. off). This would happen on high voltage OR on low temperature. On the load side I'd use the GWL BMS board hooked up to a Tyco 190A relay.

When I connect the alternator, I will parallelise the LAs and use a second Tyco relay to isolate the Li's. The GWL BMS can connect up to 3 latching relays! The third opens when 0.3V higher or lower than the min/max values you set - I'll use this for an alarm I think. But yes, the charge-isolating relay will isolate the Li's from the LAs.

 

I know, but that's not what we were asking. I wanted to know if Richard could drive a load-disconnect relay to replace his Victron Battery Protect that's between his battery and inverter - can you connect a load-disconnect relay to the Valence internal BMS to trigger on low voltage? I'm guessing not. But @Dr Bob does mention that you can get "a cheap Amazon voltage board (£10 ish) for the low voltage disconnect on the load side."

 

I found this: https://www.amazon.co.uk/KKmoon-Voltage-Detection-Charging-Discharge/dp/B019YWUI5G but it doesn't look like you can connect a latching relay, only a powered one. Any idea what to search for?

The only cheap voltage boards from Amazon that I have found won't do latching relays. You need MPs circuit. 

[jetzi]

8 minutes ago, Dr Bob said:

The only cheap voltage boards from Amazon that I have found won't do latching relays. You need MPs circuit.

Ah - I interpreted what you said as a BEP switch controlled by the BMV on the charging side and a Tyco controlled by a voltage board on the load side. What do you use to switch the voltage on the load side, if not a latching relay?

[WotEver]

14 hours ago, Richard10002 said:

Notwithstanding that, 2500W/13V = 193A, so 190A would almost certainly be fine.

Depends. If you’re drawing 2500W on the mains side, it’s pulling <2940W on the D.C. side. If the voltage has dropped to circa 12V then that’s 245A. That is why you divide mains power by 10 to determine the D.C. current. Obviously if you’ll never demand 2500W AC then it won’t be a problem but it’s important that you understand the realities of the calculations. 

[Dr Bob]

7 minutes ago, ivan&alice said:

Ah - I interpreted what you said as a BEP switch controlled by the BMV on the charging side and a Tyco controlled by a voltage board on the load side. What do you use to switch the voltage on the load side, if not a latching relay?

No, on my system the BEP disconnect isolates the Li's the LAs so stops both charging and loads. I have only one disconnect. That is the simple way of doing it and it has worked great for 12 months. Tom has both the BEP and a tyco i.e. 2 disconnects, one for charging and one for loads. I think he uses a BMV on the BEP to do the loads but for charging he has an alternator controller that does the latching tyco relay. That alternator controller is now not available - it's gone commercial and costs £500.

[jetzi]

22 minutes ago, Dr Bob said:

No, on my system the BEP disconnect isolates the Li's the LAs so stops both charging and loads. I have only one disconnect. That is the simple way of doing it and it has worked great for 12 months. Tom has both the BEP and a tyco i.e. 2 disconnects, one for charging and one for loads. I think he uses a BMV on the BEP to do the loads but for charging he has an alternator controller that does the latching tyco relay. That alternator controller is now not available - it's gone commercial and costs £500.

Ah yes, sorry Bob I remember now. When the Li's are disconnected you run your domestics from LA.

 

Yes, the alternator side is definitely the tricky bit. @Richard10002 what are you using to disconnect your alternator? I'm going to try to live domestically on solar alone for the first few months while I figure out how to tackle that monster. But leaning towards a Tyco relay, opened on high voltage by the GWL BMS, that will isolate the alternator/lead acid/engine side from the solar/lithium/domestic side.