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Old 17-10-2022, 06:38   #1
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Making a cheap BMS ABYC compliant

Just a heads up for those worried about their alternator getting fried, or insurance demanding ABYC compliance:

I looked at the cheapest Daly Smart BMS for an 8s 24V strings of cells. This is a 30A version with Bluetooth and an app that allows configuration and full details of what is going on inside the battery. Here is a link: https://www.amazon.com/Protection-Bl.../dp/B09YNZP9MZ
These BMS’s are MOSFET based: the battery negative connects to the BMS and the BMS provides another negative to be used by the boat’s electrical system.

You can easily hack this:

1. From the positive terminal of the battery, connect first a class T fuse, then a Blue Sea Systems remote battery switch, then to the main positive busbar.

2. From the negative terminal of the battery, connect a direct cable to the main negative terminal, skipping the BMS.

3. Connect the BMS B- cable to the battery negative as well.

4. Connect the BMS cell balance leads to the battery cells.

Now you have everything connected except for the P- cable. You can connect to the BMS with their Bluetooth app and set everything up as you wish. Whenever the BMS determines everything is fine, the P- cable is connected to battery negative. When the BMS wants the battery to switch off, it disconnects the P- cable from battery negative.

All one has to do is create a mechanism to convert this signal of P- disconnecting from battery negative into what you want: which is first disabling chargers and or hight loads, then a couple seconds later, send a disconnect pulse to the Blue Sea systems RBS to disconnect the battery. This mechanism can be done old school, with relays, fly-back diodes and a time delay and pulse circuit or a little more refined using a microcontroller, relay for the warning signal and a little transistor to turn the RBS off. Anyone with a little Arduino experience can do this, even with an ATTiny.

Daly also sells a similar BMS for dual bus: instead of the single P- output, it also has a C- output, which is the negative for charge sources. This is even better because with that extra signal you can create separate warning outputs for stopping charging and stopping discharging.

All the above without opening up and modifying the BMS
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Old 17-10-2022, 06:43   #2
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Making a cheap BMS ABYC compliant

I don’t see how the original or the mod impact on the ABYC compliance or not.

Nowhere does ABYC require high side disconnect.

So equally you could just use low side disconnect. It has its drawbacks but so what in reality.

I don’t understand what specific problem is the issue here. Y
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Old 17-10-2022, 07:00   #3
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Re: Making a cheap BMS ABYC compliant

Quote:
Originally Posted by goboatingnow View Post
I don’t see how the original or the mod impact on the ABYC compliance or not.

Nowhere does ABYC require high side disconnect.

So equally you could just use low side disconnect. It has its drawbacks but so what in reality.

I don’t understand what specific problem is the issue here. Y
It is required to output the warning signal before the disconnect happens. You know, to stop the alternator from frying rectifier diodes etc.
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Old 17-10-2022, 07:02   #4
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Re: Making a cheap BMS ABYC compliant

An alternative and probably better method is to ignore the P- and C- connection completely and instead monitor its CANbus output. This does require a bit more than an ATTiny but a $7 Arduino Micro can do it
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Old 17-10-2022, 07:28   #5
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Re: Making a cheap BMS ABYC compliant

I haven't tested this or even had a closer look at the source, but there is a plugin for Victron's Venus OS that is supposed to get this information over the BMS's Serial-Interface: https://github.com/Louisvdw/dbus-ser.../wiki/Features

Would the Cerbo relay this information ("raise alarms from the BMS" on the above list?) to the other connected devices, so that they shut themselves down?

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Old 17-10-2022, 07:31   #6
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Re: Making a cheap BMS ABYC compliant

Quote:
Originally Posted by s/v Jedi View Post
It is required to output the warning signal before the disconnect happens. You know, to stop the alternator from frying rectifier diodes etc.
Actually no it doesn't require a warning signal to disconnect alternator just recomends an audible one.
See note 2 in the screen grab.

There are simple adjustable high and low volt alarms many under 10 bucks . I need to install a high volt alarm .
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Old 17-10-2022, 07:37   #7
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Re: Making a cheap BMS ABYC compliant

Quote:
Originally Posted by goboatingnow View Post
I don’t see how the original or the mod impact on the ABYC compliance or not.

Nowhere does ABYC require high side disconnect.

So equally you could just use low side disconnect. It has its drawbacks but so what in reality.

I don’t understand what specific problem is the issue here. Y
Actually it does require a high side disconnect.
Although tABYC is just recommendations
E13 does state all lithium battery marine installations require a BMS .
Hence a HVD
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Old 17-10-2022, 08:39   #8
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Re: Making a cheap BMS ABYC compliant

Quote:
Originally Posted by newhaul View Post
Actually no it doesn't require a warning signal to disconnect alternator just recomends an audible one.
See note 2 in the screen grab.

There are simple adjustable high and low volt alarms many under 10 bucks . I need to install a high volt alarm .
Actually, it does according to 13.9.4.1:
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Old 17-10-2022, 09:32   #9
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Re: Making a cheap BMS ABYC compliant

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Originally Posted by s/v Jedi View Post
Actually, it does according to 13.9.4.1:
That's what I dont like about the ABYC they are behind a paywall. I don't have full access to the documentation. Thank you for posting their recommendations.
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Old 17-10-2022, 11:20   #10
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Re: Making a cheap BMS ABYC compliant

Quote:
Originally Posted by s/v Jedi View Post
Just a heads up for those worried about their alternator getting fried, or insurance demanding ABYC compliance:

I looked at the cheapest Daly Smart BMS for an 8s 24V strings of cells. This is a 30A version with Bluetooth and an app that allows configuration and full details of what is going on inside the battery.

I went with 4 of those for my 24v build. 8S4P using 280AH 3.2v EVE cells.
I used the 30 amp ones as you mentioned and used the BlueSeas RMBS devices (one for each bank) and built my own "black box" that would pulse them using relays and R/C circuits to pulse the output.

I'm not running my alternators to my 24 volt house bank at all so that was not a concern.

It worked great and I could then push 500 amps through a single bank if ever needed. But what killed me was first that I didn't have it set up for them to be able to balance because the Daly never knew it was "charging"
The other issue was that to see individual cell information I had to run an app on my phone and "reactivate" the bluetooth on the Daly. (Would only stay on up to 1 hour) I had to do that for each bank because you connect to the BMS and the application can't look at them all at the same time.

In the end, I went with the REC-BMS for 3 big boat-bucks. I was happy to turn on the integration and remote monitoring and all those features I wanted over to someone who had already sorted it all out and integrated with my Victron stuff as well. I knew I could do it myself in other ways (CANbus) with the DALY, but my list is too long of other things to manage at this point and I had to draw the line SOME where!

But - I do like the original idea I had and I happen to have 5 of them I can let go

Always appreciate your thoughts and input Jedi!
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Old 17-10-2022, 11:45   #11
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Re: Making a cheap BMS ABYC compliant

Quote:
Originally Posted by Jenta View Post
I went with 4 of those for my 24v build. 8S4P using 280AH 3.2v EVE cells.
I used the 30 amp ones as you mentioned and used the BlueSeas RMBS devices (one for each bank) and built my own "black box" that would pulse them using relays and R/C circuits to pulse the output.

I'm not running my alternators to my 24 volt house bank at all so that was not a concern.

It worked great and I could then push 500 amps through a single bank if ever needed. But what killed me was first that I didn't have it set up for them to be able to balance because the Daly never knew it was "charging"
The other issue was that to see individual cell information I had to run an app on my phone and "reactivate" the bluetooth on the Daly. (Would only stay on up to 1 hour) I had to do that for each bank because you connect to the BMS and the application can't look at them all at the same time.

In the end, I went with the REC-BMS for 3 big boat-bucks. I was happy to turn on the integration and remote monitoring and all those features I wanted over to someone who had already sorted it all out and integrated with my Victron stuff as well. I knew I could do it myself in other ways (CANbus) with the DALY, but my list is too long of other things to manage at this point and I had to draw the line SOME where!

But - I do like the original idea I had and I happen to have 5 of them I can let go

Always appreciate your thoughts and input Jedi!
That’s exactly what I was describing, great to see it was already done successfully You did it old school, timing the relays with an RC circuit, which is good enough. I got four years of analog design in college and like it almost more than digital … almost.

Yes, I forgot to mention that this enables full 500A capability without any inefficiency from MOSFET resistance in the circuit, and the heat management this causes!

Yes, balancing gets disabled this way, but I would prefer an active balancer anyway, and only enable it when needed, which would be manually in this case.

I got to this point because I am evaluating my BMS design, finding ways to make it simpler and possibly cheaper and this was one of the ways I identified. I’ll try multiplexing and maybe even an Analog Front End but that gets into very specific purpose chips and I’m trying to stay clear of that as much as possible. I even have new ideas about using cell modules that communicate with a master controller.

Monitoring the rs-485 port would be better and allows you to report cell voltages from the Arduino. Reading the code used for the Cerbo plugin should be a time saver as it may have everything ready to cope and paste
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Old 17-10-2022, 12:13   #12
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Re: Making a cheap BMS ABYC compliant

Quote:
Originally Posted by newhaul View Post
Actually it does require a high side disconnect.
Although tABYC is just recommendations
E13 does state all lithium battery marine installations require a BMS .
Hence a HVD
Nothing in e13 requires high side disconnect , merely a disconnect is needed hence low side is certainly ABYC compliant.
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Old 17-10-2022, 12:32   #13
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Re: Making a cheap BMS ABYC compliant

Personally I blow hot and cold on MOSFET switches , either N channel high side or low side. I don’t rate P channel as Rds remains 2x N channel and costs are higher.

These days 80v 0.75 milliohm Rds n channel mosfets are available for under 10 dollars in small quantities. Hence by paralleling some , big mosfet switches can be built cheaply compared to expensive mechanical devices. Yes even this low Rds requires handling 7-15 watts of dissipation, but typically max current is only short circuit , but of course it depends what the BMS is been used for.

There is certainly an argument in removing cheap BMS mosfets but there’s equally an argument for rebuilding your own high end mosfet switch ( as well as adding advance warning as nick suggests. )

Personally a good BMS needs to output charge start stop signals , possibly tailored to each charge source , it’s needs to output alarms , and then after all fails it needs to activate the safety disconnect.

I do think there’s a need to bring nmea2000 to bear on boats electrical system. I’d like to see alternators, main chargers , mppt , and BMS all using nmea2000 to coordinate each other . Victron /Rec/ wakespeed are probably closest to this ideal, but we need more players. It’s reduces all the wiring significantly.

We could then speculate a family of boat orientated nmea2000, ie alternators , BMS , mppt, battery protectors ( load disconnects ) even shunts and Soc monitors all communicating using NMEA PGNs to control and exchange info, with the added potential bonus of MFD integration etc.

That’s were the industry will go in my opinion but we are a-ways away. This of course tend to not favour Chinese equip , as they are reluctant to get nmea certification

Given there’s now quite a body of ardunio nmea2000 compatible interface libraries there’s no reason budding electronics DIYers couldn’t build the building blocks themselves.
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Old 17-10-2022, 12:57   #14
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Re: Making a cheap BMS ABYC compliant

Quote:
Originally Posted by goboatingnow View Post
Nothing in e13 requires high side disconnect , merely a disconnect is needed hence low side is certainly ABYC compliant.
Question then does a BMS have a high voltage disconnect ?
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Old 17-10-2022, 14:19   #15
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Re: Making a cheap BMS ABYC compliant

I am very much against the nmea2000 integration as done by Wakespeed, Victron etc.

My first issue is with compatibility: there are no PGN’s for shutting down an alternator etc. and it will require a decade or more before such things would be settled.

My second issue is that my battery should work safely when ai switch my nmea off. I switch it off regularly, like when there are thunderstorms around.

I like to see the state of my batteries on a spiffy Cerbo GX display, but I do not need to see individual cell voltages there. When something internal to the battery is wrong, I expect a warning signal after which I’ll look at that data.

What I am wondering now is that maybe the Cerbo plugin that works with Daly BMS could be expanded to trigger Cerbo relays for warning signals!
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