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ePowerBank

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Hi All -- Just joined this great forum - and want to be careful about doing this the rest of my life (lol).
Seriously, looking to identify a BMS for below system and welcome any suggestions on best spot to post in forum (DIY Powerwall, BMS, Inverters?)

System: Passive Home Backup / Active Sump Backup
Equip:
Magnum MS-4448PAE (44Kw, 48v) Inverter
EVE LiFePO4 280Ah DIY Battery bank (just ordered on Alibaba)
BMS (?)

Thanks !
 
Hi All -- Just joined this great forum - and want to be careful about doing this the rest of my life (lol).
Seriously, looking to identify a BMS for below system and welcome any suggestions on best spot to post in forum (DIY Powerwall, BMS, Inverters?)

System: Passive Home Backup / Active Sump Backup
Equip:
Magnum MS-4448PAE (44Kw, 48v) Inverter
EVE LiFePO4 280Ah DIY Battery bank (just ordered on Alibaba)
BMS (?)

Thanks !

The MS-4448PAE is a 4.4KW inverter (Not 44KW)

Lets do some math.
At 4.4KW, the max continuous current on the DC side is 4400W/48 = 92 Amps.
That means your BMS needs to be rated for at least 92Amps Continuous.

If your cells will be in a place that might get cold (0deg C), your BMS needs low temp disconnect.

@OverkillSolar sells a 16S 100A BMS that might fit the bill.



 
Thanks @FilterGuy for the 44KW catch - - what a difference dots can make - - understood, agreed but embarrassed (lol).
Things I'm not sure of at this point (since this is my 1st renewable project):
- Does BMS need to interface with inverter (Magnum is old school as I understand, but reliable)?
- Inverter / Charger spec is 60 ADC charging - so is 60A charging compatible with 100A BMS?
- I understand EVE cells suggest 0.5C charge rate, therefore, 140A. Will the 140A be compatible with 100A BMS & 60A Magnum charger?

Note I'm thinking I don't need the fastest charging as these will be emergency power only: Active Sump backup & passive home backup.
I figure I should minimize the charge cycling and voltage level to lengthen the life of the batteries, not to mention have a good BMS.

Thanks for the suggestion on the Overkill Solar - I've also sent a note to confirm if 100A BMS is right one.
Thank you also for the beginner resources above - I'll take a look at the BMS one...
 
- Does BMS need to interface with inverter (Magnum is old school as I understand, but reliable)?
No. The Overkill BMS is pretty self contained. I recommended the Overkill because I knew the Magnum would not interface with a BMS very easily.

- Inverter / Charger spec is 60 ADC charging - so is 60A charging compatible with 100A BMS?
The Overkill is rated at 100A Charge and Discharge. At 60A you are only .6 of the Overkill Charge rate specification..... all good.
- I understand EVE cells suggest 0.5C charge rate, therefore, 140A. Will the 140A be compatible with 100A BMS & 60A Magnum charger?
The Eve recommends a MAX of .5C. Charging at less than .5C is even better. 60A is less than half the max cell charge rate, so you are fine However, if you add additional charge sources (like solar), be sure to keep the total under 100A or it will be too much for the overkill.

Thanks for the suggestion on the Overkill Solar - I've also sent a note to confirm if 100A BMS is right one.
The 92A discharge rate is close to the 100a rating of the BMS and I do not like running equipment at the specified max. Consequently, for your application I would prefer one that is rated at 120A or more continuous, but I don't know of one that I can recomend. However, I suspect you won't be using the full 4.4KW capability of the inverter so the actual load will probably be somewhat less than 92A.
 
Thanks for the direction @FilterGuy. I also read your resource article on BMS - very helpful.
It causes me to wonder if I'm picking the right inverter, which in part was because it seemed simple and proven.
Apparently it's common to have BMS and Inverter not interfaced much.

What's my greatest risk without the interface - the BMS detects a failure mode and can't tell inverter to shut down?
Would it be fare to say the Inverter is controls overall (bank) charge rate while BMS controls individual (cell) charge rate?
 
Note I only have batteries on order at this point, so any suggestions on best inverter / BMS combinations are welcome.

Again, this is Active (automatic) Sump Backup / Passive Home Backup system, using Magnum 4.4kw 120/240 with 280Ah of LiFePO4.
The home backup (power outage) part of this would be utilized overnight so I don't run a generator all night, but want to be careful how far I draw down the batteries. My bank I figure is 13.4kwh, where I figure worst case wintertime would 10kwh (probably more like 8kwh) if heater is going and I sleep a full night, before kicking on the generator...
 
What's my greatest risk without the interface - the BMS detects a failure mode and can't tell inverter to shut down?
If the overkill decides there is a failure (such as low voltage), it will turn off all power to the inverter and the inverter will shut down... so in a rather abrupt way, the inverter *is* signaling the inverter by shutting off power. This is a tried and true way of operating...... as long as the BMS is rated for the currents involved. One cautionary note: I don't recall the brand, but one brand of solar chargers specificly says that if they are shut off from the battery it can damage the SCC. I would avoid any such charger.

What pushes me to more sophisticated signalling between the BMS and the Inverter is when the current gets higher than the available BMSs can handle. Your described situation is right on the cusp of that, but the Overkill should still be OK. If you needed 110A.....I would be advising differently.

One way people work around the current limit on FET based BMSs is to have multiple batteries in parallel. In your case, it would be two banks of 16 cells, each with it's own overkill BMS.... then the total current from the two batteries would be 200A.

The next option is to use signals from the BMS to turn contactors or SSRs on-off to control the current. This is essentially the same model as the FET based BMS like overkill but the FETS are external to the BMS. To tell the truth, I have never done this. If I am in this situation I go to the next option.

One step more sophisticated is to use the signals from the BMS to turn the inverters and loads on&off rather than try to turn the current on&off. However, to do this there has to be a way of controlling the inverters, chargers, and loads. The best brand of inverters and chargers for this type of set-up is Victron (particularly for inverter-chargers). However, there are other brands that can be made to work.

The final level of sophistication is when the BMS tells the loads & Chargers to turn on/off via a network of some type. There are a few BMSs that have developed the necissary protocols to talk with some specific equipment, but if they don't specificly say they can talk to the equipment you want, assume it can't even if it has the same network interface (like CANBus) Currently the industry is pretty fragmented so there is no standard. That means the choices of what can work with what is pretty limited. Maybe in the future there will be standards that make this a lot easier to 'plug and play'

Would it be fare to say the Inverter is controls overall (bank) charge rate while BMS controls individual (cell) charge rate?
I am not sure I would say charge rate.... I would probably say the Inverter controls the battery charge voltage and the BMS does not let the charge voltage for either the battery or the cells get out of bounds.

Charge rate is more or less an accumulation of what all the chargers are pumping into the battery. Many BMSs can monitor this and shut off charging if it gets too high.
 
Wow - thank you again. So there's always a weak link somewhere.
If I understand correctly, I need at least 92A (4400w/48v) for my inverter and can't go over 100A if I use the the Overkill 100A.
According to inverter spec's, I can 5sec surge to 167A, and 30sec surge to 125A, or 30MIN to 100A (see attached).

What pops (breaks, burns, ??) if I go over the 100A?
Sorry if this is a repeat, anything wrong with a 200A Daly (if they even make it)?

Basen Technology as both a Daly option as well as others I think are Basen branded - I could add to my battery order.

I'm not doing solar in this case, which I think only helps this topic.
I'm attaching my crazy plan here, what I call Active Sump Backup and Passive Home Backup.
I'm doing the batteries as a DIY pack, so it's about 1/2 the cost of retail, and will be in my basement so not as concerned about environment.

Thank you for the input !
 

Attachments

  • Backup Power Plan 2021 0414.pdf
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  • MS-PAE-series_datasheet_64-0275_RevE_web_0.pdf
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If I understand correctly, I need at least 92A (4400w/48v) for my inverter and can't go over 100A if I use the the Overkill 100A.
According to inverter spec's, I can 5sec surge to 167A, and 30sec surge to 125A, or 30MIN to 100A (see attached).
I would contact Overkill and see what he says about the surge numbers....
What pops (breaks, burns, ??) if I go over the 100A?
The FETs in the BMS will overheat and burn out.
Sorry if this is a repeat, anything wrong with a 200A Daly (if they even make it)?
Daly makes a lot of different BMSs. They came out with their 'smart BMS about a year ago and a lot of folks on the forum have had issues with them so I would avoid them.

The Daly non-smart BMSs have historically been reasonably solid but:
1) They do not have low temp disconnect,
Since your cells will be in the basement maybe this is not an issue.

2) they are not programmable
This is not necessarily bad, but their limits are set rather aggressively and you can't change them. The normal day-day controll and voltage limits will be driven by the inverter so the BMS only comes into play if the Inverter does not stop charge or discharge in time.

3) There is no data interface to see what is happening at the cell level.
In my mind, this is only a factor if something isn't working and you are trying to figure out what is going on. However, some people are data hounds and really like to see what is going on at all times. Having said that, this may be the biggest drawback. Just this week I was working with a guy that had a Electrodacus and I am not sure we would have been able to debug his issue without the cell level data.

4) The Daly BMS charge rate is usually about 1/2 their discharge rate. (If I read the page correctly, the Daly you linked to only has a 100A charge rating.) If you only have 60 or so amps for charge this is not a big limitation.
.
 
Thank you @FilterGuy .
Re #1) yes, I'll stay away from Smart Daly's
Re #2) seems disappointing if Daly isn't programable
Re #3) I'd rather have more then less info (since most of my $$ is in the bank), so I think that means continue this study
Re #4) sounds like this may help
Conclusion: While Daly comes with a plus (charging up to 150A) it comes with some big minuses.
hmmmm
-------------------------------------
I think I'm going to change to another inverter, so this may be all for nothing. Going to switch from from Magnum to Growatt 5kw.
Not sure if that puts me over the top with Overkill (5000W/48V=104A) ?
I think I'll still follow your advise and ask Overkill if there's any room in their fig's.
Stay tuned....
 
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