Replacing a drop in batteries BMS with your own

[alctel]

Has anyone done this?

Mainly I was looking at https://www.electriccarpartscompany.com/12v-400ah-preferred-lifepo4-lithium-battery-packs

Which are really well made inside with a strong case and good internal connections but the BMS is a bit crap and has no external connection.

There is a lot of room in the top and I think I could fit a rec BMS in there, and the case is far superior than anything I could make on my own.

Thoughts?

[jordanbigel]

Well, I am waiting for 3 of them to be delivered this week.

> but the BMS is a bit crap and has no external connection

As for this, I'm not sure how you came to this determination, as far as the first part, I am really not equipped to judge. But I can tell you for a fact that you a re wrong about the second part.

See this document for details:
https://www.electriccarpartscompany....-pack-4-27.pdf

the tl;dr of it is that the Pro version offers a 3 connector harness. One connector provides signals for low/high voltage warning, low/high current warning, low/high temp warning, another provides signals requesting cooling or heating, as the case may be.

However, if by "has no external connection" you really mean it has some external connections, but no CanBUS port and does not have the same cell monitoring capability as a battery with an external BMS, then you are right.

Also, if you have not seen the teardown video, but it sounds like you may have since you said the battery has good construction.

https://www.youtube.com/watch?v=F2ynIbGsc1E

I intend to wire the warning signals to a single relay to shut down the alternator and also to the Multiplus AUX1 (using the "two signal bms" assistant) to shut down charging/inverting in case of a warning from the batteries.

For me, I don't want to build my own packs, and from what I have seen the ECPC packs will do the job and have the required connectivity capabilities to ensure not blowing them up by overcharging, etc.

I remain curious about what you know regarding the BMS involved - frankly, I did not ask them what brand it was because I don't know enough to evaluate them.

[alctel]

Fair enough, maybe I should have said the BMS is a bit crap for MY use case . (Although the cutoffs are set a bit high for my liking)

I built my own pack around 6 years ago so I guess I'm looking for more control and flexibility. I saw the pro option with the external connection - the problem for me is that I want a dual bus system, where it sends seperate signals for low voltage cutoff as well as high voltage. That BMS just seems to send one signal for everything.

What with the newer tech as well a canbus enabled BMS that can control charging would be the goal.

I saw the teardown, thanks - it's what got me interested in them. Way better case/construction than I could do myself for the same price.

[jordanbigel]

Originally Posted by alctel

Fair enough, maybe I should have said the BMS is a bit crap for MY use case . (Although the cutoffs are set a bit high for my liking)

I built my own pack around 6 years ago so I guess I'm looking for more control and flexibility. I saw the pro option with the external connection - the problem for me is that I want a dual bus system, where it sends seperate signals for low voltage cutoff as well as high voltage. That BMS just seems to send one signal for everything.

What with the newer tech as well a canbus enabled BMS that can control charging would be the goal.

I saw the teardown, thanks - it's what got me interested in them. Way better case/construction than I could do myself for the same price.

I believe everything you said is correct.

Time will tell if I made a mistake and end up wishing I had more control. At this point, my feeling is there are enough controls to enable me to avoid destroying the cells, which is my main (really, only) goal.

As for the cutoffs being set a bit high, based on everything I have read to date, I agree with you on that also. But, I have also read many times that you should not rely on the BMS to control normal battery charging, so I am not so concerned about the high cutoffs, I figure my charge controllers will all be programmed to prevent that.

All that being said - if I find myself 12 months down the line wishing I had more control, I'm going to be very glad I followed this thread, and I hope you share more about what you learn and especially if you ever do it! Who knows, a BMS upgrade might be something I am interested in down the line.

[alctel]

They'll probably work just great for you! I know there is at least one other person here happy with them

I'm just a bit of a control freak

[Emouchet]

Do you have a strategy to handle a potential load dump from the BMS ?

Say you motor all day long, batteries are now full charged and run a bit too hot or too high state of charge, so the BMS cut the load output. Suddenly, no instruments, no light, no chart plotter, nothing...

[jordanbigel]

Originally Posted by Emouchet

Do you have a strategy to handle a potential load dump from the BMS ?

Say you motor all day long, batteries are now full charged and run a bit too hot or too high state of charge, so the BMS cut the load output. Suddenly, no instruments, no light, no chart plotter, nothing...

I think I addressed this question in post #2, but I will expand on it if you are curious. Don't mean to hijack the thread, sorry to the OP.

>>batteries are now full charged and run a bit too hot or too high state of charge

The charge controller (voltage regulator) will not allow this condition to occur. It will be programmed to stop charging long before "full". With a 1200ah capacity bank, I don't anticipate needing to keep the bank anywhere near full.

So, if the BMS detects voltage, temp (or current) creeping up too high, it will send a warning signal to the voltage regulator well before the BMS cutoff threshold which will shut down the alternator gracefully. Problem averted, hopefully.

But, if by some series of failures, the BMS does disconnect the batteries, I have also installed a Balmar AP device to protect the alternator, and, I am seriously considering adding the additional protection of an ArgoFET isolator which will allow the eng battery to take up any alternator output in case the BMS relay fails.

I also have the ability to run house loads off the starter battery in case the house bank gets shut down. And, I have a 3rd "bank" - a single battery in the bow for the thruster and windlass, which has its own dedicated alternator. This battery can also be paralleled with the house/engine bank to provide more power to house loads in a battery failure scenario.

[Rumrace]

I’m absorbing about 25% of this. Great info thank you folks

[Rumrace]

I have 3 banks 2batteries up front 4 in back and one crank. 400ah house.
I love this modular unit. Going to read up on dimensions weight country of origin. The new charger has not damaged any of the batteries. Does seem to switch to another battery well before one is fully charged.
The front batteries are new lipo but never seem to get a full charge. They are not connected to the house switch.

[Dirk01]

Originally Posted by alctel

Has anyone done this?

Mainly I was looking at https://www.electriccarpartscompany....-battery-packs

Which are really well made inside with a strong case and good internal connections but the BMS is a bit crap and has no external connection.

There is a lot of room in the top and I think I could fit a rec BMS in there, and the case is far superior than anything I could make on my own.

Thoughts?

Take a look to https://www.taoperf.com/
That's what you want to have ...

[alctel]

Originally Posted by Dirk01

Take a look to https://www.taoperf.com/
That's what you want to have ...

This looks nice, but doesn't seem to be able to talk to a wakespeed alt regulator and the victron integration stuff seems a bit thin, no documentation that I can find on it.

if that changes by the time I get my battery finally I'll definitely look into it more

[fxykty]

Originally Posted by alctel

This looks nice, but doesn't seem to be able to talk to a wakespeed alt regulator and the victron integration stuff seems a bit thin, no documentation that I can find on it.



if that changes by the time I get my battery finally I'll definitely look into it more

Check again, all that is needed is on the website.

Regarding the Wakespeed regulator, if it is the WS500 then the communication is via CANBUS.

[alctel]

Wakespeed speaks a slightly different flavour of CANBUS though, I'd be weary of assuming it worked without seeing someone else using it

[alctel]

I actually emailed the toa people - I was wrong about the wakespeed, it can talk to it.

Looks like a good solution, just very expensive!

[fxykty]

Originally Posted by alctel

I actually emailed the toa people - I was wrong about the wakespeed, it can talk to it.

Looks like a good solution, just very expensive!

You get what you pay for - just compare the feature set. I don’t know of any other BMS that matches the features, but YMMV.