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Mecer LiFePO4 Lithium Ion Batteries: Any experience


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5 hours ago, lyndiesel said:

My question is  - with the built in BMS system in the batteries - am I correct in understanding that there will be no physical BMS connecting data cable to the inverter - other than the charging / load cables?

Hello @lyndiesel You're right, there'll be no comms between the battery and the inverter. The more experienced members of this forum might be able to share some workarounds that you might want to explore since electronics is your forte :)

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On 2021/04/22 at 3:05 PM, Rooney Hat said:

Absolutely something to consider,

But would have to pay around 40k to get to 8.something kwh 80% DOD in Lithium,

or just spend 20k to double AGM capacity from 4 to 8 200ah. getting me a total of 19.6 (9.8kwh with 50% DOD) with the idea that I wouldn't use that amount every night thus extending the battery life of all. Provided they don't fail me.

I wouldn't spend any more on AGM :)

Once these fail - look at a lithium option.

One thing not mentioned before (seems there's only negatives at this point with AGM) is mixing different aged AGMs is not recommended. So if 1 of your pack of 4 breaks 6 months from now  - it's replacing it with a single new one is not recommended - this is as far as I remember from all the "experts" a few years ago. Maybe 6 months is not accurate, but rather after a good number of cycles - don't know what exactly, but the internet should be able to advise. Lithium has no such issue - you can add an additional pack any time -as the electronics take care of any cell differences etc.

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8 minutes ago, Igubu said:

I wouldn't spend any more on AGM :)

Once these fail - look at a lithium option.

One thing not mentioned before (seems there's only negatives at this point with AGM) is mixing different aged AGMs is not recommended. So if 1 of your pack of 4 breaks 6 months from now  - it's replacing it with a single new one is not recommended - this is as far as I remember from all the "experts" a few years ago. Maybe 6 months is not accurate, but rather after a good number of cycles - don't know what exactly, but the internet should be able to advise. Lithium has no such issue - you can add an additional pack any time -as the electronics take care of any cell differences etc.

Just had this very discussion with my brother earlier today. I'm happy to see that I'm learning a lot from these streets 😃

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7 hours ago, lyndiesel said:

Hi guys, I have a strong background in electronics, but pretty new to Lithium battery technology - especially BMS systems and CAN system link ups. I am about to set up a Sunsynk inverter system in a week or so - and an installer has suggested these Vision/Mecer Lithiums as a 10kW battery option - 4 x 12V 200Amp items in series.

My question is  - with the built in BMS system in the batteries - am I correct in understanding that there will be no physical BMS connecting data cable to the inverter - other than the charging / load cables?

The inverter has a pretty decent BMS built in - but worried about how well the inverter can estimate the SOC of this battery bank? will it do so on the voltage/current flow alone?

Thanks

Lyndon

Hi Lyndon,

As always check with the manufacturer on their advise, but only if they are experts with Lithium (LifePO4 in your case) as a technology. It is very different to LAcid batteries, units like yours should not require any balancing. I'd be careful to just connect them in parallel to self balance - in some cases you risk damage to the "unintelligent" BMS'es inside.

If you were ordering individual cells for a DIY build, then an initial balance could help a little, but it's more for capacity check etc - here a link to a well respected guy who explains a little bit about it. - Note this relates to DIY specifically.

What you can do - use a multi meter, DC of course to handle 14+V and measure the individual batteries to see if they are close to each other. If they are - just get them connected on your inverter, and run it a few cycles like that. Then disconnect them and measure individually again  - they should be very close to each other, as the BMS inside controls charge/discharge.

If one of your pack is way out (not sure if you have 2 or 4) I'd charge that up with a Lifepo4 charger first. You mention you don't have one - so perhaps a good idea to get one (think Victron sells a good one for not to much -you don't need high Amps - 5 - 10Amps or so are more than enough) - and charge them individually and then connect them up.

Make sure you have a high enough rated  DC disconnect/ Fuse box for total Amps between them and the inverter. ( both negative and positive) - If you are paralleling 4x of these, a buzz bar might be needed to avoid them fighting with each other, but check with the supplier. As explained previously - these batteries don't usually have smart BMS systems inside, so they don't know about master/slaves in a pack, and doesn't talk intelligently to each other.

 

 

Edited by Igubu
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2 hours ago, nembudziya said:

Hello @lyndiesel You're right, there'll be no comms between the battery and the inverter. The more experienced members of this forum might be able to share some workarounds that you might want to explore since electronics is your forte :)

Correct - no CAN/RS485. On your inverter these will be setup as "AGM" - and some settings around charge rates, discharge rate, V settings for full etc - and also some things to disabled as well which were needed for LAcid - but not for lithium. Again the supplier should be able to give you all the settings, or at least the solar installer.

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On 2021/04/29 at 12:35 PM, lyndiesel said:

My question is  - with the built in BMS system in the batteries - am I correct in understanding that there will be no physical BMS connecting data cable to the inverter - other than the charging / load cables?

The inverter has a pretty decent BMS built in - but worried about how well the inverter can estimate the SOC of this battery bank? will it do so on the voltage/current flow alone?

I would seriously consider spending more money for a battery with effective comms to the inverter. These Mecer units have no easy way to access the cell voltages etc so you are quite limited in the extra control you can add. Unless you're going full DIY with your own BMS, I think you're getting your money's worth on proper comms.

As you hinted at, the "BMS" on the inverter just looks at total voltage of the batteries in series. No individual cells or even individual banks. No way of knowing actual SOC, which is critical for best optimization of battery life/utility. I originally ran my battery like this but quickly developed a DIY solution for comms because I saw how inefficient it was. Fine if it's just backup, but painful for everyday cycling.

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On 2021/04/27 at 11:23 PM, nembudziya said:

For some context, I'm a newbie (you probably know this if you've been following this thread) without any fancy equipment at my disposal. So I have no special LiFePO4 charger lying around to assist with top balancing. So I was thinking that parallel connecting them might help with balancing them out before the inverter can charge them after installation. Any thoughts would be much appreciated.

I would hook each 12V battery up seperately to a normal car battery charger (assuming you have access to one) and charge each to max voltage (13.8V?) - just need to watch it doesn't over charge as some cheap batteries chargers are prone to doing! This way you know all of them are close to fully charged before putting them all in series. This is called top balancing.

Parallel connecting only works when you are actively charging them. It is an option here as well if you have a big enough car battery charger. Ideally you want to charge at greater than 5% C-rating. So here you have 200Ah batteries, so charging at 10A (200 x 0.05). But if you have 4 in parallel, you now need 4x10A=40A charging. Not easy to get a car battery charger doing that... (read expensive...)

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14 minutes ago, JaseZA said:

I would seriously consider spending more money for a battery with effective comms to the inverter. These Mecer units have no easy way to access the cell voltages etc so you are quite limited in the extra control you can add. Unless you're going full DIY with your own BMS, I think you're getting your money's worth on proper comms.

As you hinted at, the "BMS" on the inverter just looks at total voltage of the batteries in series. No individual cells or even individual banks. No way of knowing actual SOC, which is critical for best optimization of battery life/utility. I originally ran my battery like this but quickly developed a DIY solution for comms because I saw how inefficient it was. Fine if it's just backup, but painful for everyday cycling.

Tried to explain the advantages of proper CAN, etc a few times, but yet people continue to buy cheap lithium based purely on advertised capacity :) in this instance they were bought already, so just giving some pointers.

I’d be very hesitant to stick an old car charger onto them- easy to damage (and the warranty will be void Im sure)- so dont think there is any need to top balance them- just follow the advice given previously around making sure each individual 12V pack are more or less the same V. They are brand new - and should be balanced already, different pack voltages are fine, the individual BMS will sort that out if they are relatively close to each other.

 

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On 2021/04/30 at 1:05 PM, Igubu said:

They are brand new - and should be balanced already, different pack voltages are fine, the individual BMS will sort that out if they are relatively close to each other.

The installer came today and seems this was just about right. He recommended using the AGM setting on the inverter and I wasn't sure if that was right but he's the "expert" so I was kinda stuck. Any thoughts?

IMG-20210502-WA0013.jpeg

Vision SP 12-200 LiFeP04 User Manual.pdf

Edited by nembudziya
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Hi guys

 

New to this, so please excuse me. Looking at getting the an 200ah Mecer battery and pair it with inverter/charger I have at home already. The only info that I have on it is that it is a 1000w 12V Sky King Pure sine wave inverter, not sure what rate it charges at. Will the BMS look after the battery and prevent over charge? 

 

Any risk leaving it plug in permanently on charge in case of loadshedding?

 

I would also like to add a solar panel and charge controller (MTTP) to the system to go off-grid with my TV, sound and modem. Would a 400w - 500w panel be sufficient?

 

Any help will be appreciated.

 

Thanks

Jacques 

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