Separate port BMS

[smith85]

Hi all, hoping to get some advise on a BMS for a system with a specific purpose.
I'm replacing the battery bank in a sail boat (currently 3 AGMs) with 3x diy 100ah lifepo4.

The cells are being wired into three separate banks of 4 cells (12v), with an individual BMS for each bank. I'm aware this can be avoided by wiring in parallel first, but as the install in on a boat possibly hundreds of miles from a shop having a heavily redundant system is preferred.

I intent to use a Daly 100ah BMS on each and the main power generation will be solar/wind with the alternator as a backup. I'm considering using a separate port bms as the costs are much the same, and should there be an issue the solar charger will remain connected to the battery in most cases and no possibility of being damaged.

53.51US $ 22% OFF|smart lifepo4 bms 4s 12V 24V 36V 48V 60V 30A 100A Li Ion 3S 8S 10S 12S 13S 16S 24S 18650 bluetooth APP balance board 1A Parallel|Battery Accessories| - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

I understand the charge current is reduced using a separate port, from what I can see about 50%. So 50a (based on the 100a bms), around 600w on each. Its unlikely the power generation will ever be this high at all, and with three banks I would defiantly never hit this limit.

Are there any other downsides to using a separate port over a common port? What are your thoughts?

 

[rickypr]

I also have a 3x 100Ah AGM batteries and will change them for one 3x 280Ah 3.2V batteries. What BMS did you end up using?

 

[smith85]

I think you might have miss-described your new batteries. I'm assuming it's 3 packs of 4x 3.2v cells. Giving 3x 280Ah 12v packs. Sorry to nitpick, but someone will correct it in 6 months time otherwise, and it might confuse others researching similar systems

I ended up using three individual separate port Daly BMS's.
However, if I started again I think I would probably use three common port BMS's.
The separate port ones are working perfectly, but it makes the installation more complicated for little benefit.
Also it makes adding battery monitor shunt almost impossible as they require a common negative and cannot be connected to the positive side. I think it is possible to get a battery monitor with twin negative shunts (1 for charge and 1 for discharge) but they are VERY expensive.
I finally settled on a bi-directional hall effect battery monitor (cheap off eBay). It's working well and seems to be very accurate, much more than expected.

A common port BMS will make your life easier though.

FYI, the remainder of the system was put together with a Renogy DCC50s and a couple of 160w panels. Then two further 100w panels with a separate Renogy MPPT charge controller were added about a month ago.
We are a sailboat so the engine is run as little as possible. We have an excess of power now, to the point we're running an investor and a 1200w immersion heater on occasion to have hot showers ??

 

[rickypr]

Sorry, you are completely right! I will have 4x 3.2v batteries to make one 12v 280Ah battery. I was going to purchase 32 batteries for my home system and ended ordering 4 extra to use on the sailboat. I was thinking about using a separate port BMS, but I will rethink everything per your suggestion.
I was also looking at Renogy's DC-DC chargers.

Nice to have excess power and hot showers on the boat!

Cheers

 

[smith85]

Perfect, you should end up with a really effective system.
The Renogy stuff all seems really good quality. Just be careful not to overtighten the terminals as it's possible to strip the thread or even shear them off. I managed the latter on the DCC50s and had to open it up to replace the terminal ?‍.

 

[Steve_S]

Separate port BMS just as a separate Charging Input line so whatever charging devices (SCC, AC-DC Charger, etc ) can feed the battery pack whenever they are needed. The Discharge side will do just that and only that, so feed the DC gear, Inverter and so on. IF you have a combined Inverter with Charger (typically used for shore power to charge batts and/or passthrough AC) then this would not be capable of charging said pack as that is a "common port" configuration.

Common port is the simplest, as it allows for charging & discharging on the same wire pair going to the battery packs. This allows for Charging & discharging concurrently as well. Additionally, for Combo's like the All In Ones (SCC, Inverter/Charger) and combined Inverter/Chargers this is the only way to go really.

The tricky bit is to ensure you properly parallel your battery packs when making up the bank. The load/charge splitting between the packs is best if it is all balanced with same length wires and identical configurations. This Victron Document is great on how to do this properly. https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf

 

[vientoymar]

I think you might have miss-described your new batteries. I'm assuming it's 3 packs of 4x 3.2v cells. Giving 3x 280Ah 12v packs. Sorry to nitpick, but someone will correct it in 6 months time otherwise, and it might confuse others researching similar systems

I ended up using three individual separate port Daly BMS's.
However, if I started again I think I would probably use three common port BMS's.
The separate port ones are working perfectly, but it makes the installation more complicated for little benefit.
Also it makes adding battery monitor shunt almost impossible as they require a common negative and cannot be connected to the positive side. I think it is possible to get a battery monitor with twin negative shunts (1 for charge and 1 for discharge) but they are VERY expensive.
I finally settled on a bi-directional hall effect battery monitor (cheap off eBay). It's working well and seems to be very accurate, much more than expected.

A common port BMS will make your life easier though.

FYI, the remainder of the system was put together with a Renogy DCC50s and a couple of 160w panels. Then two further 100w panels with a separate Renogy MPPT charge controller were added about a month ago.
We are a sailboat so the engine is run as little as possible. We have an excess of power now, to the point we're running an investor and a 1200w immersion heater on occasion to have hot showers ??

why didn't you connect the shunt between the negative battery and the bms?, usually - B port. you will get all that goes to the battery. if you have three batteries, three shunts, or you have only one fuel indicator for all of your tanks?
also, you should know how each battery works, in case one is with degradation you won't see it in only one shunt.

 

[smith85]

why didn't you connect the shunt between the negative battery and the bms?, usually - B port. you will get all that goes to the battery. if you have three batteries, three shunts, or you have only one fuel indicator for all of your tanks?
also, you should know how each battery works, in case one is with degradation you won't see it in only one shunt.

Yes I guess this could have worked, but I prefer to have 1 overall monitor rather than three individual too keep track of. I don't think I've seen any other setup using multiple shunts and monitors to keep a check on each battery.
I use a hall effect monitor on the main battery positive and this works very well for me.

 

[vientoymar]

have you the link of that monitor?

how long have you been working with this system? . I'm really afraid of connecting the LFP in parallel and what will do when you reconnect after a bms shutdown. Was thinking to change into LFP, but the issues with alternator charging are not very clear and other problems like this do me still in lead.

 

[smith85]

have you the link of that monitor?

how long have you been working with this system? . I'm really afraid of connecting the LFP in parallel and what will do when you reconnect after a bms shutdown. Was thinking to change into LFP, but the issues with alternator charging are not very clear and other problems like this do me still in lead.

The battery monitor is this one,

Battery Monitor Meter Wireless DC 120v 100a Volt Amp Ah Soc Remaining Capacity for sale online | eBay

Find many great new & used options and get the best deals for Battery Monitor Meter Wireless DC 120v 100a Volt Amp Ah Soc Remaining Capacity at the best online prices at eBay! Free delivery for many products!

www.ebay.co.uk

The system is in a boat, we are live aboard and have been using for around 8 months.

You will need a DC battery charger (with lithium charge profile) if you're charging off an alternator. Never connect the lithium cells directly to the alternator, it can damage the battery and the alternator.

 

[vientoymar]

thank you for the link.

yes, I know, but are more problems, in case of a bms disconnect with the alternator and the scc, all of them have solutions but I think still not ready and secure for my boat.