Need a BMS fast

[Bert06840]

Originally Posted by john61ct

Wut?

bulldust

I hold over a dozen patents on lithium battery technology. How about you?

I have 100C rate cells on my desk. I work with those things for a living. How about you?

So now we are done with the flexing: yes, I’m obviously aware of the hard physical limitations being beyond 2C. The insult wasn’t necessary.

But that doesn’t change the fact that designing a 4S/12V system for 500A is not the safest, not the smartest or the most cost efficient.

If you want to draw 5kW for any length of time, a 4S system is bad design practice.

EDIT: one of the reasons why you want to stay away from kilo-Amp ranges, is that one of the biggest hazards is copper vapor inhalation. You make one mistake working on your 500A rated battery and you drop a bus bar across the terminals. What happens? A lithium system designed for 500A has many kilo-Amps of short circuit current capability. You see a flash, you inhale. That’s what humans do when shocked - and I don’t mean electrically. Just when you inhale, there’s a cloud of vaporized copper in front of you.

Allegedly it is excruciatingly painful, and incurable.

So. Can you do a 500A system? Sure. Should you? Only when it is the best option, which in this case it is not.

But hey. It’s a free country. People do whatever they want. People ask for advice, I share mine. It doesn’t make it law or universal truth.

[rffffffff]

Originally Posted by Bert06840

I hold over a dozen patents on lithium battery technology. How about you?

I have 100C rate cells on my desk. I work with those things for a living. How about you?

So now we are done with the flexing: yes, I’m obviously aware of the hard physical limitations being beyond 2C. The insult wasn’t necessary.

But that doesn’t change the fact that designing a 4S/12V system for 500A is not the safest, not the smartest or the most cost efficient.

If you want to draw 5kW for any length of time, a 4S system is bad design practice.

EDIT: one of the reasons why you want to stay away from kilo-Amp ranges, is that one of the biggest hazards is copper vapor inhalation. You make one mistake working on your 500A rated battery and you drop a bus bar across the terminals. What happens? A lithium system designed for 500A has many kilo-Amps of short circuit current capability. You see a flash, you inhale. That’s what humans do when shocked - and I don’t mean electrically. Just when you inhale, there’s a cloud of vaporized copper in front of you.

Allegedly it is excruciatingly painful, and incurable.

So. Can you do a 500A system? Sure. Should you? Only when it is the best option, which in this case it is not.

But hey. It’s a free country. People do whatever they want. People ask for advice, I share mine. It doesn’t make it law or universal truth.

Hey Bert, glad to have your experience here. You mention that a 4S 5kw battery is not the best idea. I’m thinking of an 8S or 8S/2P 24v battery to run my 24v inverter that can surge to 5kw (pretty sure, gotta recheck that, but let’s use that number for the sake of the discussion) and will run 3kw continuous.

I have the inverter and 24v booster pump already so I’m stuck with 24v. I could see a 225a draw from the inverter and DC loads in a worst case scenario. I’m curious if this fairly common setup presents issues to your eyes or if there’s a better way to go about this whole thing that I’m not seeing. Are we collectively making dumb mistakes that you see as we build batteries?

[Bert06840]

I want to make my own mistakes, so I'm not going to deprive anyone from the right to do the same

The key thing I wanted to get across earlier is that very high current systems can be incredibly violent. People need to treat batteries with respect. The short circuit current of a LFP battery is at least 100 times its capacity rating. A 100Ah battery will happily give you 10kA and perhaps several times more. Think an arc welder, running at 100A. Times 100 or 200. That's what you get when you short these things out. You'll get a massive flash and the arc will be many thousands of degrees vaporizing anything in its path.

I just thought it was my obligation to make people aware of this.

But yeah... 3kW continuous from a 24V system is quite doable. You will need at least 200Ah/5kWh of capacity to support that, preferably double.

As a matter of fact, my own bus is designed for exactly the same numbers! I got three 5kWh BYD batteries in parallel. Each fused at 100A. I'm comfortable with those ratings.

Use eye protection.

[rffffffff]

Thanks for this. I’m going to use 8 or 16 if the chinese 280ah cells eventually, can’t wait to build it.

I am super afraid of shorting battery terminals as I work on them so I usually keep things covered with cardboard as I work to lower risk and am considering plasti-dip of some form for some of the battery tools to do the same. I’ve been shocked by 750vdc one time, albeit low current, but that experience led me to not mess around much afterwards.

Thanks for the posts!

[john61ct]

I'm not saying 24V isn't better for high power systems.

Just that peak rates over 2C are not a problem for quality cells whether 20Ah or over 200Ah.

That statement has in fact nothing to do with voltage.

Yes, if it is practical to go to a higher voltage system in order to reduce ampacity, save money on copper for long runs

that's a good way to go.

[kazetsukai]

Originally Posted by RobOfYork

What I still am confused with is how it prevents over charging of a cell.

I have two of these (SBMS0) for my current Tesla bank.

Overcharge protection: The SBMS0 shuts off the Victron MPPT by connecting two of the the SBMS0' EXTIO leads to the Remote port on the Victron MPPT.

Your solar charge controller needs a physical remote port for the SBMS0 to control it.

Over discharge can be solved the same way using a Victron BatteryProtect.

Where did you order the Daly BMS from?

Originally Posted by Bert06840

But that doesn’t change the fact that designing a 4S/12V system for 500A is not the safest, not the smartest or the most cost efficient.

If you want to draw 5kW for any length of time, a 4S system is bad design practice.

I look at any system with >100A expected draws/charge rates with suspicion...

[RobOfYork]

Originally Posted by kazetsukai

Where did you order the Daly BMS from

I ordered it from the DALY store on Aliexpress. I let them know that I was going to be contacting my bank and then suddenly... They offered to send another one by DHL. That one actually came in less than a week.

If they would have just done that when I first started chatting with them about it never showing up... Instead of months of... It's on it's way my friend, pe patient... I would have been a happy customer.

[kazetsukai]

Originally Posted by RobOfYork

I ordered it from the DALY store on Aliexpress. I let them know that I was going to be contacting my bank and then suddenly... They offered to send another one by DHL. That one actually came in less than a week.

FWIW I ordered both my 4S (12V) 100A DALY and 16S (48V) 250A DALY Smart from Amazon, the 12V one arrived in 3-4 days and the 48V one arrived 3 weeks later.


Electrodacus' 4 units (ordered from electrodacus.com) each arrived around 2-3 weeks after ordering.

[BigPaul367]

Originally Posted by RobOfYork

Apparently I was scammed by DALY. I ordered a 250amp bms from them and it's now way over a month overdue. All they say is "wait my friend" I am going to go ahead and do a chargeback. They can't give me a real answer.

Where can I get a BMS that is either a 200amp or 250amp quickly?

I need it for a 280AH lifepo4 12 volt battery I am building.

Help and thanks!

Here is the problem, everyone has a Covid Excuse, AND all the large BMS Systems come from China. I have built two 250 AMP Battery Systems. Both of the BMSs came from reputable sources. Two months for the first one and two months three weeks for the second. The Advantage, for me, was I already knew it was going to take a long time. I relayed this information to my Customers. I was lucky to have them understand, both systems used 250 AMP BMSs. Small batteries, BIG power. When dealing with China, instant gratification does not exist. Sorry!

[RobOfYork]

Originally Posted by BigPaul367

Here is the problem, everyone has a Covid Excuse, AND all the large BMS Systems come from China. I have built two 250 AMP Battery Systems. Both of the BMSs came from reputable sources. Two months for the first one and two months three weeks for the second. The Advantage, for me, was I already knew it was going to take a long time. I relayed this information to my Customers. I was lucky to have them understand, both systems used 250 AMP BMSs. Small batteries, BIG power. When dealing with China, instant gratification does not exist. Sorry!

I paid the extra for fast shipping. I was told it would be delivered by April 12th. That never happened. I would have been much more patient with them if I would have NOT paid for the fast shipping. At first I just asked them to refund just the extra I paid for the fast shipping. They just told me to be patient.

You can take an excuse so long before you have to do something about it. In my case, just telling them I was contacting my bank got it shipped out with the method I paid for the very next day.

This experience has made me no longer trust DALY. I'll be using the electrodacus in all future builds.

[kazetsukai]

Originally Posted by RobOfYork

This experience has made me no longer trust DALY. I'll be using the electrodacus in all future builds.

The plus to Electrodacus is that it has two stage under/over voltage protection for smart charge/discharge, optional Wifi / UART capabilities (although difficult to consume the compressed data stream), has a slick built in UI and supports a variety of chemistries.

The downside to Electrodacus is that first, by itself it has no means of enforcing under/overvoltage protection- it needs additional hardware capable of talking via a remote port, the current model (SBMS0) is limited to 8S unless you use a pair like I did, and its worst problem is born out of these in that it makes everything much, much more complicated.

DALY and similar offerings on the other hand makes things very simple. There are some smart offerings but typically you order a BMS specific to your cell count/chemistry, you wire it up and plug it in- done. The battery protection offered isn't two stage, so no smart charge/discharge management- it is meant to disconnect the pack as a last resort to protect cells from damage or fire.

I would like it if Electrodacus did a 16S+ BMS, as the wiring for a pair is needlessly complex for my use case, and while pairing was presented to me as a potential solution to my dilemma (during the 24V-48V upgrade) other problems came of it. I also really don't like the IDM /ribbon cable balance leads, which aside from an breakout board there's no alternative.

[RobOfYork]

Originally Posted by kazetsukai

Overcharge protection: The SBMS0 shuts off the Victron MPPT by connecting two of the the SBMS0' EXTIO leads to the Remote port on the Victron MPPT.

I looked at my current equipment and I do have a Victron MPPT. My power inverter also has a remote on and off switch. I think I can use that to connect to the SBMS0. Still researching on that.

[kazetsukai]

Originally Posted by RobOfYork

I looked at my current equipment and I do have a Victron MPPT. My power inverter also has a remote on and off switch. I think I can use that to connect to the SBMS0. Still researching on that.

Keep in mind that you also need to shut off DC appliances in the case of overdischarge protection.

[RobOfYork]

Originally Posted by kazetsukai

Keep in mind that you also need to shut off DC appliances in the case of overdischarge protection.

Yep, I still need to research the DC side. What I am trying to find out now is how much of a load you can still leave on the DC side with a cell out of balance for a short period of time until you can correct the situation.. Like leaving one 3 watt light circuit on and disconnecting everything else.

Over discharge should blow the main DC fuse out if sized properly to protect the battery from having to heavy of a load pulled on it. At least I think it would. I may be wrong. Still researching this too.

[rffffffff]

Originally Posted by kazetsukai

Keep in mind that you also need to shut off DC appliances in the case of overdischarge protection.

A lot of people use the Victron battery protect device for the DC side, it’s really simple.

[RobOfYork]

Originally Posted by rffffffff

A lot of people use the Victron battery protect device for the DC side, it’s really simple.

I'm assuming the battery protect is between the battery and "normal" DC load only and the inverter could still be wired directly to the battery bypassing the battery protect?

This way you would have a way to disconnect all loads independently.

Basically I'm brain storming this.

[rffffffff]

Originally Posted by RobOfYork

I'm assuming the battery protect is between the battery and "normal" DC load only and the inverter could still be wired directly to the battery bypassing the battery protect?

This way you would have a way to disconnect all loads independently.

Basically I'm brain storming this.

Exactly, it has a simple way to interface with the electrodacus and can handle a lot of amps of dc load, plus they’re not terribly expensive.

[kazetsukai]

Originally Posted by rffffffff

A lot of people use the Victron battery protect device for the DC side, it’s really simple.

+1. They can be used on their own (which can only see the pack voltage) or in conjunction with the Electrodacus (which can see pack and cell voltage).

In terms of wiring the VBP only allows for one-way current (you can't charge and discharge through them- only one or the other). So e.g. you need to place the BP just upstream of something like a DC fuse block, but downstream of a common bus bar where your charge sources are connected.

Multiple VBPs can be used to create a tiered system for DC appliances- cutting out superficial stuff earlier on to keep critical loads going longer, which will restore in reverse order as energy becomes available. You'd put one VBP for one DC fuse block and another for a different fuse block, set one to a higher voltage cutoff. An example would be a DC charge port used specifically for a CPAP or something similar.

My discharge strategy is to have the inverter cut out at 20% SoC, most DC appliances at 10-15%, then whole system shutoff at 5%.

Even the largest VBPs are not suitable for use with inverters, do not put inverter loads on them.

[Rucker]

Interesting thread. I have a Daly 250A but their website is a bit confusing and I didn't get the one with BlueTooth, so that is on order now.

I decided to go Daly on my 208 AH LiFePo because at the time when I was researching Daly was the recommended unit, and most of the other units seemed either knock-off or cheap, or a duplicate to my Renogy 40A solar charge controller. The markeplace is still really confusing to me.

A BMS is a squidgy term, since they don't all have all the same features. I was looking for over/under voltage shutoff, programmable, low temp monitoring and active cell balancing. The Daly I have just does over/under voltage shutoff, programmable, and low temp monitoring (as does the Renogy). Apparently the Daly does a terrible job of cell balancing so I bought a cool little capacitor-based active balancer for thirty bucks that seems to do a fantastic job (https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1).

What else should come in a BMS for LiFePo?

[rffffffff]

Originally Posted by kazetsukai

+1. They can be used on their own (which can only see the pack voltage) or in conjunction with the Electrodacus (which can see pack and cell voltage).

In terms of wiring the VBP only allows for one-way current (you can't charge and discharge through them- only one or the other). So e.g. you need to place the BP just upstream of something like a DC fuse block, but downstream of a common bus bar where your charge sources are connected.

Multiple VBPs can be used to create a tiered system for DC appliances- cutting out superficial stuff earlier on to keep critical loads going longer, which will restore in reverse order as energy becomes available. You'd put one VBP for one DC fuse block and another for a different fuse block, set one to a higher voltage cutoff. An example would be a DC charge port used specifically for a CPAP or something similar.

My discharge strategy is to have the inverter cut out at 20% SoC, most DC appliances at 10-15%, then whole system shutoff at 5%.

Even the largest VBPs are not suitable for use with inverters, do not put inverter loads on them.

Great info. Thank you.