Jump to content

New to this forum and would appreciate some advice


Nick W
 Share

Recommended Posts

Hi All

I recently installed a Victron Easy Solar 24v/3000va/70amp inverter and am using 2 x Blue Nova 13v/108Ah/1400Wh Lithium Iron batteries connected in series. I am not using the solar panel option at this time but may do so in the months/years to come.

My problem arises when we have load shedding and I am using about 350w per hour and only seem to get just under 4 hours of supply. I have now been informed that you should not connect Lithium Iron batteries in series.

Can anyone please help me with advice on what to do as I have spent a lot of money on a system that really isn't working that well for me

Thanks

Nick

Link to comment
Share on other sites

The problem with lithium batteries and a series connection is that they are always managed by a BMS (Battery Management System). These systems help make the battery safe (so it is a must) and also help optimise it's charge/discharge by balancing the cells and doing protections. 

These protections and charge/discharge management is the problem with series connections, as each of your batteries has it's own BMS and they don't know of the other. If one battery is fully charged it will block charging, also o blocking the other battery. If a protection happens, this will also block the other battery as well. So both batteries are not fully charge or fully discharged.

The best is to buy the battery matched to your system (a 24V Blue Nova in this case would work well). It's a bit late as you already have the 2x 12V batteries. The best option I can think of is to get a battery balancer over each battery. 

Link to comment
Share on other sites

1 hour ago, Nick W said:

you should not connect Lithium Iron batteries in series

Oh of course you can! Well, at least speaking in general. Each of those 12V batteries are already composed of 4 cells in series.

But as Louis said, the issue is that each battery contains its own BMS, and quite often the manufacturer did not design the battery with series operation in mind. So now you have two separate BMSes and no way for one to know what the other is doing.

I think what is happening in your case is simply that one battery runs out before the other, and that is perfectly normal. One cell inside one of the batteries will always be empty first, because no two cells are ever exactly the same. What could be playing a role is that because there is no cross-battery balancing happening, one battery probably fills up first and causes the other one to have a hard time fully charging, in which case I agree with Louis: A normal 12V balancer might do the trick.

Remember also that running batteries in series when the supplier said not to, will typically void the warranty. At the very least don't tell them you did that...

Link to comment
Share on other sites

So when charging the highest charged battery switches off both batteries when that battery is charged and the other battery doesn't reach full charge.

When discharging the lower charged battery switches off both batteries, while the other battery still has some in the tank.

Seems to me that if you top balance the two batteries, that the issues should be minimized.

Connect them both in parallel and charge them at the correct charge voltage for a day or two, and your issues should not be as bad.

Alternatively, get a HA01 battery balancer.

 

 

Edited by phil.g00
Link to comment
Share on other sites

I noticed that Blue Nova themselves have a product that uses two 12V batteries in series. Their CPS product uses two 12V batteries with no visible appearance of a balancer, unless it's hidden. I also think a HA01 would be a good option. 

Otherwise, give Blue Nova Support a call.

https://www.bluenova.co.za/wp-content/uploads/2020/07/BN_CPS3000-2.8k.pdf

 

Link to comment
Share on other sites

53 minutes ago, Ingo said:

I noticed that Blue Nova themselves have a product that uses two 12V batteries in series. Their CPS product uses two 12V batteries with no visible appearance of a balancer, unless it's hidden. I also think a HA01 would be a good option. 

They designed the BMS with series-connection in mind. Or at least they probably did...

Let me tell you a secret: The Victron SmartLithiums also don't have an cross/module balancing. All it has is two analog signals, one to indicate a stop-discharge, and another to indicate a stop-charge condition, which connects to an external protection and/or comms module that protects the battery.

I think @phil.g00 above made the most important point: You got to start off with them balanced. So put them in parallel for a few days with a charger that holds the voltage nice and high (around 14.4V). Then put them back in series.

Link to comment
Share on other sites

21 hours ago, Nick W said:

2 x Blue Nova 13v/108Ah/1400Wh Lithium Iron batteries connected in series..... I am not I have now been informed that you should not connect Lithium Iron batteries in series.

This is Bluenova's response to me 2 weeks ago about connecting the MPS/"lead acid drop-in" replacements is series (and parallel if anyone want to know). So series connection of the Bluenova "Lithiums" should not in it self be a cause for concern.

For Series configuration preparation:
Charge each battery individually till they are all fully charged.
Connect all batteries that will be in the same series string in parallel, and charge together till they are full.( draw less than 1Amp from the charger if this can be measured).
Connect in series and charge with your series configured charger. Please take note of the batteries charge voltage and current specifications on our website, as this would be crucial for your warranty.
 
Parallel Configuration connection:
Charge each battery individually till they are all fully charged.  
Connect all batteries that will be in the same parallel string in parallel, and charge together till they are full.( draw less than 1Amp from the charger if this can be measured).  
Connect to your charger for parallel configuration.
Please take note of the batteries charge voltage and current specifications on our website, as this would be crucial for your warranty.
 
21 hours ago, Nick W said:

I recently installed a Victron Easy Solar 24v/3000va/70amp inverter and am using 2 x Blue Nova 13v/108Ah/1400Wh Lithium Iron batteries connected in series. 

My problem arises when we have load shedding and I am using about 350w per hour and only seem to get just under 4 hours of supply.

As mentioned by the other posters, one issue could be that the 2 batteries are not balanced (equally charged/discharged) but I would also look at the seemingly too obvious option that the settings on the Easy Solar are creating the impression of much lower than expected capacity. In other words, if the inverter low DC shutdown settings are too high then the inverter will shut down long before the battery is actually at the point where it needs to shut down - especially if potentially using lead acid type voltage settings (the victrons generally come setup "out of the box" ready for lead acid and you/installer need to make some changes to the voltage settings etc. for the Bluenovas). 

So the question is whether the battery is actually "flat" after 4 hours (and assuming the 350W load is fairly stable this seems unlikely).

Also the question of whether the battery is consistently flat after 4 hours at roughly 350W or only about every other time of use? What I have found while playing around with the inverter/battery settings is that depending on your settings the very flat discharge curve of the LiFePO4 batteries will sometimes mean that a bulk charge is not initiated following something like load shedding because the battery voltage did not drop low enough... now you get another use cycle (i.e. load shedding) with a slightly heavier load and you "run out of battery".

very long way to get to:

Post your Easy Solar battery settings (bulk charge voltage, max charge/discharge current, Float voltage, etc). to double check

Link to comment
Share on other sites

22 hours ago, Louisvdw said:

The problem with lithium batteries and a series connection is that they are always managed by a BMS (Battery Management System). These systems help make the battery safe (so it is a must) and also help optimise it's charge/discharge by balancing the cells and doing protections. 

These protections and charge/discharge management is the problem with series connections, as each of your batteries has it's own BMS and they don't know of the other. If one battery is fully charged it will block charging, also o blocking the other battery. If a protection happens, this will also block the other battery as well. So both batteries are not fully charge or fully discharged.

The best is to buy the battery matched to your system (a 24V Blue Nova in this case would work well). It's a bit late as you already have the 2x 12V batteries. The best option I can think of is to get a battery balancer over each battery. 

Hi Louis

Thanks very much for your advice .... I think I will have to bite the bullet and get the 24v battery suited to my system

Regards

Nick

Link to comment
Share on other sites

22 hours ago, plonkster said:

Oh of course you can! Well, at least speaking in general. Each of those 12V batteries are already composed of 4 cells in series.

But as Louis said, the issue is that each battery contains its own BMS, and quite often the manufacturer did not design the battery with series operation in mind. So now you have two separate BMSes and no way for one to know what the other is doing.

I think what is happening in your case is simply that one battery runs out before the other, and that is perfectly normal. One cell inside one of the batteries will always be empty first, because no two cells are ever exactly the same. What could be playing a role is that because there is no cross-battery balancing happening, one battery probably fills up first and causes the other one to have a hard time fully charging, in which case I agree with Louis: A normal 12V balancer might do the trick.

Remember also that running batteries in series when the supplier said not to, will typically void the warranty. At the very least don't tell them you did that...

Thanks very much for the advice

Think I am going to get the new 24v battery

Regards

Nick

Link to comment
Share on other sites

19 hours ago, phil.g00 said:

So when charging the highest charged battery switches off both batteries when that battery is charged and the other battery doesn't reach full charge.

When discharging the lower charged battery switches off both batteries, while the other battery still has some in the tank.

Seems to me that if you top balance the two batteries, that the issues should be minimized.

Connect them both in parallel and charge them at the correct charge voltage for a day or two, and your issues should not be as bad.

Alternatively, get a HA01 battery balancer.

 

 

Thanks for the advice Phil

Will give that a bash

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...