How to Fogstar battery?

[ivan]

Has anyone done a 'how to?' on creating a DIY Fogstar battery to work with the ME3000SP? Tempted to buy some and make a new battery bank, but don't know how the cells are connected together and what to use as a BMS etc, settings etc. Sounds like quite a few of you guys have already done this - is there a standard set of instructions out there somewhere?

[Stinsy]

Has anyone done a 'how to?' on creating a DIY Fogstar battery to work with the ME3000SP? Tempted to buy some and make a new battery bank, but don't know how the cells are connected together and what to use as a BMS etc, settings etc. Sounds like quite a few of you guys have already done this - is there a standard set of instructions out there somewhere?

There are a few projects detailed on here. I think Joe's thread is called "Idiot's guide", Casium's is called "Yet another", Nowty's is called "DIY battery project", and so on...

However, it really isn't complicated!

1) Buy cells.
2) Assemble into a battery. You can buy specially designed cases, or use duct tape, or some other method, but the batteries like being tightly enclosed.
3) Fit a balancer. Some people have run these without a balancer and monitored the cell voltages carefully, finding that they don't diverge significantly. However, a balancer is strongly advised.
4) Set the max charge voltage and min discharge voltages in the ME3000SP (or whatever model of inverter/charger you have). 3.6V and 3V per cell (57.6V and 48V for a 16s pack) are pretty conservative values.
5) Proffit.

The main thing to be REALLY careful of is: these cells have an astonishingly low internal resistance and you have no option but to connect them live. Therefore insulated tools and a meticulous attitude are essential (You can wrap your spanners in electrical tape if you don't want to buy new ones).

[nowty]

You either buy a full well know BMS and it can be set to pretend to be a Pylontech battery or similar.

Or like me you run with a simple cell balancer and set the ME3000SP to lead acid (note, you have to plug in a temp sensor or spoof it with a fixed resistor).

My ME3000SP battery settings for a 16 LFP cell configuration in lead acid mode are,

1 Set battery type DEFAULT (Lead Acid mode)
2 Set battery capacity 999Ah (the max it will go to, I have over 1800Ah)
3 Set discharge depth 90%
4 Set max charge current 60A (it can go even higher to 65A if your brave)
5 Set over protection voltage 56.0V
6 Set max charge voltage 55.0V (This is a little low, but my Sunny Island is set to 55.68V)
7 Set max discharge current 60A (it can go even higher to 65A if your brave)
8 Set low protection voltage 45.9v
9 Set min discharge voltage 47.0v (I would recommend this being 49.5V but one of my battery banks can go lower due to being a different chemistry)
10 Set empty discharge voltage 46.0V
11 Set full charge voltage 55.5V

My step by step thread using Fogstar batteries is here, many other threads are available,
viewtopic.php?p=57255#p57255

If you want an easy life, buy one of the many DIY carcass kits available from Fogstar or Aliexpress.

[ivan]

Thankyou - have located the threads.....there is a lot of stuff in there!!

Im very tempted to have a go. Got 20kWh at the moment, but I'm getting battery-envy reading about the size of your battery! My recent twin-ME3000P setup has dropped my daily import from about 2kWh down to 0.5kWh (unfortunately can't tell the people in holiday lets to stop cooking their tea when the load gets too high!). Any recommendations for a decent BMS to use? There seems to be a lot to choose from and I have no idea what the differences are

[Stinsy]

Most on here have gone for a basic, cheap, active balancer. However you can go for a full-function BMS if you want to check individual cell voltages without getting your multimeter out…

[Marcus]

Jk bms had a good reputation and were the most fully featured i think. i have a couple: one basic, one smart. But then JK went bit off with a lack of customer service for a while - not sure if they've gotten over it or not; Seplos seem to be a popular alternative but I have no experience of them.

It depends what you want:

Basic bms with 'built in' settings are fairly cheap, and should protect your battery from accidents. Typically what would be inside a ebike battery or similar: it disconnects when the battery is fully 100% charged, or 100% discharged, and monitors individual cells so none of them go outside the built in limits. But those limits are generally the full limits of the cells, and don't give you good cycle life if you actually rely on the bms to stop charge/discharge. They usually have a basic 'top-balance' system that works well enough, but as you cannot 'tweak' when it starts you generally have to fill the battery to 100% regularly for the balancing to work.

The smart bms's allow you to configure parameters to suit you, and can include active balancing - usually top balancing, but as you can choose the minimum balancing voltage, it can be active as long as you want. They generally can emulate off the shelf battery comms, so can play nice with smart inverter systems*. And of course you can check what it's doing on your phone app.

*I've read that whilst the jk bms's support multiple bms's in a master/slave comms system, they don't reliably report the condition of all the batteries to the inverter system

Or if you're confident your system won't take your battery outside it's design voltage/current limits, you can manage without a bms, just a fuse/breaker for overcurrent, and an active balancing unit.
The limits of this option are:

If the active balancing works all the time (as opposed to top balancing), then with lifepo4 voltage being very flat around 50% charge, the balancer can actually take the cells further away from balanced state.

If you take the battery towards 100% or 0% charge, without individual cell monitoring, you may take some cells outside their recommend voltage range whilst the whole battery voltage is still within range; you won't know how close you can get to 100% or 0% without experimenting, and with an active balancer running all the time, the limits will vary depending on what charge state the battery has spent time balancing at recently.

[ivan]

Think I want to go for something reasonably sophisticated so that I minimise abuse of cells. Main goal is to avoid user-intervention if possible - just like an off-the-shelf battery pack, and to maximise safety - so no danger of anything catching fire! I generally charge to 100% and let the batteries discharge to 20% with my pylons. I guess I should maybe charge to 80% in the summer months, but can't remember where in the settings I can change that on the ME3000.

[Stinsy]

Think I want to go for something reasonably sophisticated so that I minimise abuse of cells. Main goal is to avoid user-intervention if possible - just like an off-the-shelf battery pack, and to maximise safety - so no danger of anything catching fire! I generally charge to 100% and let the batteries discharge to 20% with my pylons. I guess I should maybe charge to 80% in the summer months, but can't remember where in the settings I can change that on the ME3000.

If you want to put your new pack in parallel to your Pylontechs then you need a 15s rather than 16s pack. And that actually reduces the requirement for a BMS, because the BMS in the pylontechs does the heavy lifting. You also don't have to change any settings in your inverter the pylontechs communicate it directly. A balancer is still highly recommended, and will do a way better job than the "top balancer" found inside a typical BMS).

You'll just notice your battery takes a lot longer to charge/discharge!

[ivan]

Damn! Went to order some this afternoon to take a leap into the great unknown - and they're now sold out.