Adding another lipo battery?

[steven2002]

I have a roamer 300ah battery fitted and would like to add another battery.
I had thought seatbase may be easiest.then when checking prices I see the fogstar 230 is £799 posted. and a roamer is £1125 plus £50 postage.
So can I get the fogstar and mix batteries?
The van has a 25a b2b fitted and I will probably add another 40a one.
Thanks

 

[bigtwin]

There’s a video somewhere on YouTube where someone did a test on this scenario.

He used IIRC a 5Ah battery in parallel with a 100A battery and they behaved on charge/discharge exactly as theory would suggest (i.e. the charge and discharge currents were split/shared in ratio to their capacity/resistance).

Ian

 

[steven2002]

So does that mean it is ok to add the different battery?
Thanks.

 

[bigtwin]

So does that mean it is ok to add the different battery?
Thanks.

I think that was his conclusion from the test he did. HOWEVER, he made a point of discussing/adjusting the BMS on each battery prior to undertaking the test.

I can only advise that you search YouTube and consider the contents of the video and judge whether it’s relevant to your own situation.

Ian

 

[bigtwin]

So does that mean it is ok to add the different battery?
Thanks.

I think that this is the video that I saw (but it seems, from searching YouTube just now, that other similar videos are also out there).

Extreme LiFePo4 Battery Parallel Test

Ian

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[Raul]

Al long as both bms es have the same settings dialled in. Roamer is not user adjustable, if fogstar is, then all you need to do is find the roamer parameters that’s dialled in, and mirror them on the fogstar.

 

[daveclare]

I spoke to Roamer about the same thing. Their advice was no. They even said that buying and adding the same battery type and output, at a later date needed to be done in a way that balanced the cycles of each battery. To ensure you get the best from both.

But what do I know. I can only rely on what I've been told. Best contact Roamer.

 

[RogerIvy]

Sometimes you will be lucky and sometimes not.
We’re currently testing four different batteries in parallel and one battery is doing more work than the other three put together. All around 280-300 ah, identical BMS with identical settings, just the cells are different.

 

[Hoovie]

In a good battery factory QC dept, not only do they test the individual cells so they have have matched sets to go into a battery pack, they will also test and record the individual completed batteries for levels so you can have matched batteries.
Depending on the manufacturer and the retailer, you will get matched sets, but buy sporadically, you can get mismatches.

having a cell in a battery pack that is notably different to the other cells will mean that cell will either do more work - or less work, depending how it differs - than the rest of the cells.
The exact same thing can happen between battery packs, so it is not surprising that if you take 4 batteries out a box and one happens to have a better cell set, that will do most of the work, or indeed just about all of it.

I see the exact same thing on my own Motorhome battery setup (except the effect is by design). I have 5 batteries in parallel and in general use, two of my batteries do 99% of the work and the other 3 the remaining 1%. This is solely due to the voltage differences between the batteries - 2 of them sit at around 13.2V and the other 3 at 12.7V, and it is always the batteries at the higher voltages get the use.
Obviously my example above is an extreme example and you would never have that much difference between batteries of the same technology, but even small variances can have a significant effect

There is an generally agreed theory that when buying Lead batteries, match the batteries to be the same ages, specs and brands ideally. This does in many ways hold true for Lithium, but there is a tendancy to think all Lithiums are the same so that principle gets ignored.

 

[Raul]

You can parallel lithium packs if you know how to. If mismatched cells hapens to be in a pack, it only comes down to capacity. The internal resistance is so low, that when we cycle with much less than 1C, the cells carry the same amps. It will only drift when you close to 1C, but you should size and design for 0.3C and have a happy life. I have parallel packs with identical bms and settings. There are times that one pack is ahead 0.2A over the other, nothing to worry. It can be down to one connection, crimp or bus bar, there so many connections that can imbalance the resistance between two packs, not just the packs them self's.

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[steven2002]

Thanks everyone this isn't looking as straightforward as I was hoping.
I will just wait a while and decide to get another roamer or sell the roamer and go all fogstar.thanks again everybody.
Cheers,Steven.

 

[Raul]

Thanks everyone this isn't looking as straightforward as I was hoping.
I will just wait a while and decide to get another roamer or sell the roamer and go all fogstar.thanks again everybody.
Cheers,Steven.

I think will be the safest route to keep them the same.

 

[bigtwin]

I see the exact same thing on my own Motorhome battery setup (except the effect is by design). I have 5 batteries in parallel and in general use, two of my batteries do 99% of the work and the other 3 the remaining 1%. This is solely due to the voltage differences between the batteries - 2 of them sit at around 13.2V and the other 3 at 12.7V, and it is always the batteries at the higher voltages get the use.

A lead acid/LiFePo4 hybrid arrangement.

Ian

 

[Hoovie]

A lead acid/LiFePo4 hybrid arrangement.

Ian

Indeed so. The key with the hybrid parallel setup is the voltage differential. Exploiting it as a feature rather than being a problem

 

[bigtwin]

Indeed so. The key with the hybrid parallel setup is the voltage differential. Exploiting it as a feature rather than being a problem

Indeed. It does however go against conventional ‘wisdom’ and that prevents many from even contemplating its legitimacy.

Ian

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[Hoovie]

Indeed. It does however go against conventional ‘wisdom’ and that prevents many from even contemplating its legitimacy.

Ian

That is because if you connect lead and lithium together, your van will explode. It's a fact coz I saw it on a youtube video

(luckily I forgot to watch those videos a couple of years ago when I did this )

 

[Gromett]

In a good battery factory QC dept, not only do they test the individual cells so they have have matched sets to go into a battery pack, they will also test and record the individual completed batteries for levels so you can have matched batteries.
Depending on the manufacturer and the retailer, you will get matched sets, but buy sporadically, you can get mismatches.

having a cell in a battery pack that is notably different to the other cells will mean that cell will either do more work - or less work, depending how it differs - than the rest of the cells.
The exact same thing can happen between battery packs, so it is not surprising that if you take 4 batteries out a box and one happens to have a better cell set, that will do most of the work, or indeed just about all of it.

I see the exact same thing on my own Motorhome battery setup (except the effect is by design). I have 5 batteries in parallel and in general use, two of my batteries do 99% of the work and the other 3 the remaining 1%. This is solely due to the voltage differences between the batteries - 2 of them sit at around 13.2V and the other 3 at 12.7V, and it is always the batteries at the higher voltages get the use.
Obviously my example above is an extreme example and you would never have that much difference between batteries of the same technology, but even small variances can have a significant effect

There is an generally agreed theory that when buying Lead batteries, match the batteries to be the same ages, specs and brands ideally. This does in many ways hold true for Lithium, but there is a tendancy to think all Lithiums are the same so that principle gets ignored.

It is not something I have looked into in any great detail. That said I believe the matching process is critical for series connected cells within an Li battery. But across parallel connected batteries I can see arguments to support pro and con.

My personal take is that I would not want to mix batteries bought from different manufactures at different times in ideal circumstances. However, I am persuaded that although sub optimal I don't see any serious reasons not to do it in a pinch.
The only caveat I would suggest is that the batteries should have the same chemistry. I personally would not mix say a LiFePO4 battery with a LiCoO2 chemistry battery. But again I have not investigated this in any great details It is just something I would be completely uncomfortable doing.

 

[nabsim]

Surely the people to ask is the manufacturer unless you aren't wanting to claim under warranty if it goes badly? Personally I can't see why different make would make any difference, the individual battery BMS should take care of its own cells. I know with my make/model you can only parallel 2 battery due to BMS but was never any mention of having to be same brand. That said what I think is of no consequence to if it will work or should be done, if manufacturer says no (as they did here) you need to accept or change completely (or risk of course). Lots of smoke and mirrors with Lifepo4 methinks

 

[Hoovie]

Surely the people to ask is the manufacturer unless you aren't wanting to claim under warranty if it goes badly? Personally I can't see why different make would make any difference, the individual battery BMS should take care of its own cells. I know with my make/model you can only parallel 2 battery due to BMS but was never any mention of having to be same brand. That said what I think is of no consequence to if it will work or should be done, if manufacturer says no (as they did here) you need to accept or change completely (or risk of course). Lots of smoke and mirrors with Lifepo4 methinks

The parallel limitation thing is an interesting one. never quite understood that TBH.
One battery will not know another battery is an actual battery - it is either a source of power (like a charger) or is a load (like a light or whatever) - current goes one way or the other and doesn't care what is it from or where it is going.

there are some Lithium Batteries with "connected" BMSes, where you can connect a data cable between the batteries to keep synchronised (my two are connected with an RJ45 cable) and there will be a maximum limit for that setup.

Overall, my own take would be yes, you can mix and match, but they will not be optimized and it is quite possible a 'stronger' battery will end up getting discharged and charged frequently whilst another is rarely touched.

But it will not be dangerous. (having said that , I wouldn't mix in Lithium Cobalt or especially Lithium Polymer batteries in a bank, but I would not have them in use in a Motorhome Leisure battery ever anyway).

 

[Al n Val]

Thanks everyone this isn't looking as straightforward as I was hoping.
I will just wait a while and decide to get another roamer or sell the roamer and go all fogstar.thanks again everybody.
Cheers,Steven.

I was facing this dilemma about a month ago, I had twin 90ah Super B lithium batteries on and wanted more capacity, not being prepared to dosh out another £4k I wanted to go another route

Roamer only being 30 mins away, I wanted to give them my business but they seemed reluctant for me to pop in and have a face to face chat, and the advice was to not mix the batteries.

Fogstar who are 3.5 hours away got my business as the advice was the same, they welcomed me to collect them, and I got 100ah more capacity for £1k less.

I sold my Super B’s and the 560ah total Fogstars cost me a total of £367 after claiming the vat back so an absolute no brainer.

A month in and the Fogstar batteries are performing superbly

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[Raul]

The parallel limitation thing is an interesting one. never quite understood that TBH.
One battery will not know another battery is an actual battery - it is either a source of power (like a charger) or is a load (like a light or whatever) - current goes one way or the other and doesn't care what is it from or where it is going.

there are some Lithium Batteries with "connected" BMSes, where you can connect a data cable between the batteries to keep synchronised (my two are connected with an RJ45 cable) and there will be a maximum limit for that setup.

Overall, my own take would be yes, you can mix and match, but they will not be optimized and it is quite possible a 'stronger' battery will end up getting discharged and charged frequently whilst another is rarely touched.

But it will not be dangerous. (having said that , I wouldn't mix in Lithium Cobalt or especially Lithium Polymer batteries in a bank, but I would not have them in use in a Motorhome Leisure battery ever anyway).

That was a typo, nobody will mix lifepo4 with LiPo, when 3,65v is ful,and the other is empty. Totally different voltages.