DIY Lithium Packs, Proposal and Discussion

luthj

luthj

Engineer In Residence
DiploStrat

DiploStrat

Expedition Leader
DiploStrat

DiploStrat

Expedition Leader
Hence my comments. Will see what they say, but methinks that for cases where you have long term voltage, you need an "L" series relay (with "coil economizer") or similar.

I used one of these monsters on my Tiger, for years, with no problems, even mounted below the camper. Ordered a new one for my present truck, if only because the coil will take 24v w/out problems.
 
R

Rando

Explorer
DiploStrat said:
I am reaching out to Overkill, but, at least at first glance, to be functionally an intelligent relay with balancing. (I can hear John61ct cringing!) There are a few other terminals, temp, and, I believe, a Bluetooth card.

There is also something labeled as a "Discharge Switch," normally jumpered. Its function is said to be: It shuts off discharge current, like a battery shutoff switch. So, if I get it, it would allow me to add a manual or remote battery kill switch. But this is a signal in, not out. That is, it tells the BMS to shut off, does not tell a remote device that the BMS has shut off.

So, ignoring leakage, if the BMS opens, the battery should be an open circuit? No?

How do you wire the Blue Sea latching relay? Across the main terminals, or in line with the BMS on the negative lead? I have never used a Blue Sea latching relay, only their "S" series. Do you have to give them a pulse, or can you simply wire like a normal relay?
Click to expand...

The "Overkill BMS" is actually just a marked up version of this:
www.lithiumbatterypcb.com

4S or 3S 12V Li ion or Lifepo4 Battery smart BMS with Bluetooth function UART and RS485 communication with 60A to 120A constant current - LLT POWER ELECTRONIC

1) Application:this smart BMS can work for 3 to 4S Lithium ion or Lifepo4 Battery ,client can choose based on your battery chemistry features 2) Current : constant current of this version BMS can be made with 40A to 120A in accoridng to the different demand 3) Dimension: :Max 138*102*15mm for...
www.lithiumbatterypcb.com www.lithiumbatterypcb.com

I have one from the original source, and it works very well. You can turn the battery on and off through the app.

The BMS has a combined charge/discharge path, but can turn either or both on or off. Unless they are both off, you will read voltage at the terminals, you just won't be able to eithre source or sink current.

Unless you plan on drawing more than 100A, you don't need or want a separate relay.
 
R

Rando

Explorer
PS the switch terminals are a logic level on/off switch for the BMS. You have to turn on the switch function in software, but then a toggle switch between those terminals will turn the whole kit and caboodle on and off.
 
DiploStrat

DiploStrat

Expedition Leader
Rando said:
The "Overkill BMS" is actually just a marked up version of this:
www.lithiumbatterypcb.com

4S or 3S 12V Li ion or Lifepo4 Battery smart BMS with Bluetooth function UART and RS485 communication with 60A to 120A constant current - LLT POWER ELECTRONIC

1) Application:this smart BMS can work for 3 to 4S Lithium ion or Lifepo4 Battery ,client can choose based on your battery chemistry features 2) Current : constant current of this version BMS can be made with 40A to 120A in accoridng to the different demand 3) Dimension: :Max 138*102*15mm for...
www.lithiumbatterypcb.com www.lithiumbatterypcb.com

I have one from the original source, and it works very well. You can turn the battery on and off through the app.

The BMS has a combined charge/discharge path, but can turn either or both on or off. Unless they are both off, you will read voltage at the terminals, you just won't be able to eithre source or sink current.

Unless you plan on drawing more than 100A, you don't need or want a separate relay.
Click to expand...

Many thanks!

While I hope that I will never stress the BMS, I am dealing with two issues.

-- The first is a way to disconnect the solar panels from a solar controller in the event that the BMS shuts down the battery. In a perfect world this happens one second BEFORE the BMS drops the load, but simultaneous may be enough. The question is whether simply connecting the relay control to the + and - of the battery is enough. In other words, when the BMS disconnects, does the voltage across the terminals drop to "0"? The other option is to simply run a wire to the Victron controller as it appears to have an internal relay that will turn it off. Normally, this is done with Victron proprietary cables, but the unit I am considering appears to simply take a bare wire with 3v or more.

-- I am confirming that my B2B doesn't care if the target battery is disconnected. So this should obviate any dangers of the alternator blowing up. And, in any case, it is still connected to the starter battery, so we meet the standard of a hybrid FLA/LiFePO4 set up.

-- Haven't done my homework on my inverter/charger yet. (And yes, I am digesting all of the don't-use-an-inverter-charger comments.)

-- Related to this is the whole separate-charge-and-discharge-bus architecture recommended for marine use. In the case of an expedition truck, this may not be an issue as we have no real mission critical threads.

I think I understand what you are saying about a combined charge/discharge path, but I don't understand your comment: can turn either or both on or off. Unless they are both off, you will read voltage at the terminals, you just won't be able to eithre source or sink current.

Sorry to be dense. :(

 
R

Rando

Explorer
DiploStrat said:
Many thanks!

While I hope that I will never stress the BMS, I am dealing with two issues.

-- The first is a way to disconnect the solar panels from a solar controller in the event that the BMS shuts down the battery. In a perfect world this happens one second BEFORE the BMS drops the load, but simultaneous may be enough. The question is whether simply connecting the relay control to the + and - of the battery is enough. In other words, when the BMS disconnects, does the voltage across the terminals drop to "0"? The other option is to simply run a wire to the Victron controller as it appears to have an internal relay that will turn it off. Normally, this is done with Victron proprietary cables, but the unit I am considering appears to simply take a bare wire with 3v or more.
Click to expand...


I am not sure there is actually an issue here. While it is not 'advised' to disconnect the battery first, it has been done many thousands of times with no issue, and Victron's suggested configurations actually have this as a possibility. I wouldn't worry about it.

-- I am confirming that my B2B doesn't care if the target battery is disconnected. So this should obviate any dangers of the alternator blowing up. And, in any case, it is still connected to the starter battery, so we meet the standard of a hybrid FLA/LiFePO4 set up.
Click to expand...

Internally the B2B electronics are the essentially the same as an MPPT, so the comment above applies.

-- Haven't done my homework on my inverter/charger yet. (And yes, I am digesting all of the don't-use-an-inverter-charger comments.)

-- Related to this is the whole separate-charge-and-discharge-bus architecture recommended for marine use. In the case of an expedition truck, this may not be an issue as we have no real mission critical threads.

I think I understand what you are saying about a combined charge/discharge path, but I don't understand your comment: can turn either or both on or off. Unless they are both off, you will read voltage at the terminals, you just won't be able to eithre source or sink current.

Sorry to be dense. :(
Click to expand...

With MOSFET based switches you don't need separate charge and discharge paths. You can control the current flow in either direction using back to back MOSFETs. So you can stop the battery accepting charge current, while still allowing it to provide 'source' current and vice-versa. This is how all the drop in batteries work. In either case, you will still measure a voltage at the output terminals, but you will not be able to either source or sink current, depending on which protection is active.
 
DiploStrat

DiploStrat

Expedition Leader
Thanks! Victron tends to confirm that their charge controller doesn't care but there may be a spike. https://community.victronenergy.com...-damage-if-the-battery-is-disconnected-b.html
The 150/45 has the remote control terminal, but I don't know where to get a signal to trigger it. (This springs from my colossal ignorance of BMS theory and practice.) Does the the Overkill have a "charge enable" terminal? I only understand it as an on/off switch on the negative leg.
"So you can stop the battery accepting charge current, while still allowing it to provide 'source' current and vice-versa." How would you wire that? I only see B-, C- and the balance leads.

Again, sorry to be dense!

This is presented as the holy grail wiring, but I can't see how to use my BMS to do this. And we can debate if it is really necessary.

1598470196173.png
 
Hillbilly Heaven

Hillbilly Heaven

Explorer
The BlueSea 7701 and the Cole Hearse 880086 are identical. Do not know who makes it for who. It does require two separate pulsed signals. One to energize and one to open the relay. I thought I had read something about not energizing both signals at the same time.

HD Series Magnetically Latching Relay, 12 V Coil - Littelfuse

www.littelfuse.com www.littelfuse.com

ML Solenoid - 12V DC - Blue Sea Systems

500 Amp magnetic latching (bi-stable) solenoid provides high-amp switching under load where manual control is not required
www.bluesea.com www.bluesea.com
 
R

Rando

Explorer
There is another thread on the Victron community (which I cannot find at the moment) where someone with too much time on their hands dropped the load from their MPPT hundreds of times with an oscilloscope on the output, and it was very well behaved. It is also kind of a Heisenberg issue, if there is a load on the output it will suppress any possible spike, however if there is no load, there could be a small spike, but who would notice/care if there is no load? The proof that this is not an issue is the deployment of many thousands of drop in lithium batteries, without reports of MPPT charged controllers blowing things up.

There is not charge enable output on that BMS that I am aware of, and you would run into the issue that by the time the MPPT got the signal and shutdown, it is likely too late anyway.

If you still have some super sensitive electronics you want to protect, a clamping diode a volt or so above you max charge voltage would do the trick, and protect it regardless of the source of the spike.

You wire it up as in the diagram. Maybe a bad choice of words - you are not cutting off the current flow, the BMS is.
 
DiploStrat

DiploStrat

Expedition Leader
dreadlocks said:
Victron makes IO cables you can bang on/off with a BMS to shut down charging w/out needing to interrupt the panels..

www.victronenergy.com

VE.Direct non inverting remote on/off cable - Victron Energy

Remotely control BlueSolar and SmartSolar MPPT charge controller models using the VE.Direct non inverting remote on/off cable. Find a dealer near you.
www.victronenergy.com www.victronenergy.com
Click to expand...

Thanks, but those require a Victron BMS and don't work with the bigger controllers. In any case, it may be moot for all practical purposes.
 
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