Choosing Between a Single Large Lithium Battery or Two Smaller Ones

[cyberyacht]

I've got two 120AH KS Energy in mine. The main advantage of a pair of batteries is that it halves the current draw when you are running high demand kit. In my view that is kinder to the batteries.

 

[daveclare]

We've got two 230's. Only because we didn't have the space for one. One battery means less very thick cables.

 

[scotjimland]

same discussion here

Lithium 1 large or 2 small

As in the title, whats the thinking on Lithium batteries, is it better to have one large one or 2 smaller ones? My thinking is if you only have one and it goes boobies up your stuffed and if you have 2 the duff one can be isolated from the bank. Or are they that reliable that one would be ok?

www.motorhomefun.co.uk

 

[Lenny HB]

A little bit more work fitting two as you would need to fuse each battery and fit an isolator switch to each of them, then feed them to a common busbar.
I prefer two as for redundancy as you are covered in the unlikely event of one failing.

 

[Lenny HB]

Another advantage of two batteries you double the max current available, useful if running a big inverter.
460 ah max discharge current 200 amps
2 x 230 ah max discharge current 400 amps.

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[68c]

[QUOTE="Guigsy, post: 5447569,
...... you're just doubling your chance of a failure.
[/QUOTE]

This is true. It is a little like the old days of four engined piston airliners. Lose one on a four set up and you lose 25% power but lose one with a single and of course it 100% loss. However running four engines mean four times the chance of a faliour. Swings and roundabouts, decide which you want. A single engined reliable fighter aircraft where you can bail out, or accept the more frequent, albeit liveable, faliour with a multi-engined passenger aircraft where you cannot.

 

[Guigsy]

If it's critical that you can run a 2000w inverter, but a single battery wouldn't cope, then you've not really gained any redundancy. If one battery silently failed and your were merrily running on one, then you tried to pull more than the single battery could supply, what would happen?

 

[Raul]

If it's critical that you can run a 2000w inverter, but a single battery wouldn't cope, then you've not really gained any redundancy. If one battery silently failed and your were merrily running on one, then you tried to pull more than the single battery could supply, what would happen?

It will either work, or bms disconnect for over current, no issues.

 

[bigtwin]

The main advantage of a pair of batteries is that it halves the current draw when you are running high demand kit.

Indeed, but the more important point to note, as Lenny HB notes below, is that you can deliver double the BMS’ maximum discharge rating.

Another advantage of two batteries you double the max current available, useful if running a big inverter.
460 ah max discharge current 200 amps
2 x 230 ah max discharge current 400 amps.

Indeed, this is the most significant benefit of doubling up on the batteries.

Ian

 

[Hymerboy]

If you have 2 (say 5 year old ) lithium and one fails are you then supposed to replace with 2 new ones as with Lead or can you just add one ?

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[PeterCarole29]

The LFP does not dive much unless is under 50% charged, you will se a 12.8v. Most of the time will sit at 13.2v and above. I have a oven that draws 1440 on victron display. The max amp draw at that time is 114A or less. Being a resistive load is pretty much PF1 and all the power delivered is used.

Two batteries in parallel a very good think no doubt, but they need to be wired to a buss individually with their own fuse. They need to be treated as two individual sources. If one develops a fault, and is wired to the next, it will be to late to disconnect it. You do not wire one lithium to the next, and pick a -ve from one and a +ve from the other. I noticed this practice it’s been mentioned above, and someone may be taking this as good advise.
Each battery has to be individually fused at least. No wonder vendors recommend one instead of two, as is outside of their control how you use them, and may come back to them.

This is very interesting and i was not aware of. As you may remember i am about to install 2 x 460ah fogstars and want to get it right any chance you can do a simple drawing to show exactly the set up

 

[Raul]

This is very interesting and i was not aware of. As you may remember i am about to install 2 x 460ah fogstars and want to get it right any chance you can do a simple drawing to show exactly the set up

Hi Peter, as you will connect some serious power, I highly recommend a Victron power in, with appropriate mega fuses. It has 4 entries for positive and 4 negatives. That will enable you to connect the two batteries, inverter, and solar charger, all to a 1000A buss bar.

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Search on you tube for explorists life they have a extensive coverage and schematics, how to use a power in with fuses, or power distribution if you want the led’s

 

[Raul]

 

[Bobbejaan]

Hi Peter, as you will connect some serious power, I highly recommend a Victron power in, with appropriate mega fuses. It has 4 entries for positive and 4 negatives. That will enable you to connect the two batteries, inverter, and solar charger, all to a 1000A buss bar.

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I tend to be an old-school tightwad/MacGyver (* Delete as required), so I've often used Henley Blocks over the years @ circa £7 - £8 each for my heavy-duty multi-cable connections .... such as this (for example) :-

100 AMP SINGLE & DOUBLE POLE 5 WAY 35MM HENLEY BLOCK FOR METER TAILS CONNECTOR | eBay

100 Amp Single & Double Pole 5 Way 35mm Henley Blocks. Single Pole: 66mm x 49mm x 34mm. Double Pole: 115mm x 65mm x 55mm.

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[Raul]

I tend to be an old-school tightwad/MacGyver (* Delete as required), so I've often used Henley Blocks over the years @ circa £7 - £8 each for my heavy-duty multi-cable connections .... such as this (for example) :-

100 AMP SINGLE & DOUBLE POLE 5 WAY 35MM HENLEY BLOCK FOR METER TAILS CONNECTOR | eBay

100 Amp Single & Double Pole 5 Way 35mm Henley Blocks. Single Pole: 66mm x 49mm x 34mm. Double Pole: 115mm x 65mm x 55mm.

www.ebay.co.uk

You will not make a good connection with those, the batteries will become unbalanced not contributing equal, and not enough amps.
Those henleys are ok for rigid solid meter tails. We use fine multi strands that needs a specialists pin crimped to use the henley. And the current will be exceeded with a 3kw inverter and two 460ah batteries. The buss bar I suggested its neat, takes fuses and can run up to 1000A.

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[Hymerboy]

If you have 2 (say 5 year old ) lithium and one fails are you then supposed to replace with 2 new ones as with Lead or can you just add one ?

Anyone know the answer to this?

 

[bigtwin]

Anyone know the answer to this?

LiFePO4 batteries are not as sensitive as lead acid in this respect so I wouldn’t worry too much about adding a new LiFePO4 battery to an existing bank. I’d make sure though that the BMS settings on the battery matched those of the old batteries.

Ian

 

[Bobbejaan]

You will not make a good connection with those, the batteries will become unbalanced not contributing equal, and not enough amps.
Those henleys are ok for rigid solid meter tails. We use fine multi strands that needs a specialists pin crimped to use the henley. And the current will be exceeded with a 3kw inverter and two 460ah batteries. The buss bar I suggested its neat, takes fuses and can run up to 1000A.

Hi Raul,
I've been using Henley Blocks successfully for over 40 years, sometimes with crimped ends, sometimes with soldered ends, and most often with just plain HD multi-strand cable depending on my requirements .... and the Henley's thick solid copper Bus-bar is far heavier & more substantial in reality than the thinner Victron Bus-bar .... I've been using Henleys for 3kw (& more) @ 12v Inverters in my vehicles & off-grid installs for many years without any problem. .......... YMMV, but each to their own.

I grant you that the Victron block has the added (good) feature of being able to use Internal fuses ... BUT they cost around 15 times more than Henley Blocks, and you STILL generally end up needing or adding External fuses at the Far end of the cable.

 

[Lenny HB]

sometimes with soldered ends, and most often with just plain HD multi-strand cable

You should never, ever use soldered wire when connecting to a screw terminal block. Solder remains in a semi-liquid state and in a screw terminal under pressure it will work loose.

 

[Bobbejaan]

You should never, ever use soldered wire when connecting to a screw terminal block. Solder remains in a semi-liquid state and in a screw terminal under pressure it will work loose.

I agree that a poorly (or fully) soldered cable-end CAN sometimes work loose, but the same applies to a poorly crimped cable-end Fitting ... but I did also say that SOMETIMES a soldered cable end (& to clarify = cable "TIP") can sometimes be the best method DEPENDING on the desired requirements (and SOME Henley Block Screws have a slightly "conical" thread tip which can get a better "bite" into a soldered tip).

I also said .......... YMMV, but each to their own.

Additional Edit :- I can also add that I have never personally had a cable-end come loose OR part-from any of my Henley Block installs in over 40 years, and indeed, due to the Heavy-Duty "Double-Screw thread-fixings" of most Henley Blocks, I am confident that I could safely "hang" my considerable bulk from my Henley Block connections without any problem (apart from perhaps "Cable Strain").

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[Raul]

I don't doubt your past experience with henley, and they are very good on static installs. However in a mobile install with bumps and vibration you need lugs with bolts and spring washer for high current, or you risk a fire. Also they don't have enough entries and they are brass, a poor conductor compared to copper even aluminium is better. But its ok for static 240v AC. On larger install, or multi sources, it will force multiple block joints, adding resistance and imbalance.
As a reference so you realise what you deal with: a lifepo4 cell 280-300ah it has a internal resistance of 0.2 mohms, and 4 in a 12v pack is a 0.8miliohms. Add a connection at battery end 50-100 miliohms depending on type and integrity of that connection made, and minimum 8 connections on a 4 cell pack.
Now envisage the total path from charging source to battery, and battery to load. As you expect the system gets complicated when you add a second or third battery. It is very difficult to maintain a equal resistance path for both batteries, so you try to share it as much as possible, then branch in the last bit to the batteries of a common point. One extra washer on one branch, can unbalance one battery by few amps under charge discharge. The victron lynx buss bar its perfect as its copper, very low resistance and quite capable for 8+2 cable connection points.

I have put in parallel victron inverters in the past, they rely on good equal resistance path to synchronise, even 2-300 miliohms difference, will fail to synchronise, and AC outlet has to be equal for the output to. I have learned that, the larger the cable, the more difficult is to maintain a balance, and when big amps forces large cable, you have to work very meticulous and use high quality connections.

 

[Ditcha]

I used this method with a lynx power in on my install a couple of years back

 

[Cush]

You should never, ever use soldered wire when connecting to a screw terminal block. Solder remains in a semi-liquid state and in a screw terminal under pressure it will work loose.

Morning Lenny HB. Just starting with soldering.

Does that advice apply to domestic household plugs and little rotary switches with multi strand wire, or just big stuff with fitted terminal ends? I was planning on putting some solder on the ends before screwing down.

appreciate being schooled.
Cush

 

[MisterB]

Morning Lenny HB. Just starting with soldering.

Does that advice apply to domestic household plugs and little rotary switches with multi strand wire, or just big stuff with fitted terminal ends? I was planning on putting some solder on the ends before screwing down.

appreciate being schooled.
Cush

I invested in a cable terminal crimper, came with about 500 crimps of all sizes for multi stranded cables, much easier and quicker than soldering (in my opinion). I use it whenever I have a multi stranded cable in either the motorhome or at home, I also have a hydraulic crimper for the 'big stuff', both have been invaluable!!

Similar to this one

https://www.amazon.co.uk/dp/B0BBLTYJKD/?tag=mhf04-21

 

[Lenny HB]

Morning Lenny HB. Just starting with soldering.

Does that advice apply to domestic household plugs and little rotary switches with multi strand wire, or just big stuff with fitted terminal ends? I was planning on putting some solder on the ends before screwing down.

appreciate being schooled.
Cush

Yes everthing, copper and solder have different expansion rates which causes problems under compression.

Best practice is to crimp a ferrule onto the wire.

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[tinkertaylor]

All this crimping going on, does anyone have their crimpers calibrated?

My old company used to supply calibration certificates for the crimpers used in control panels supplied to certain industries.

I have seen a few poorly crimped cables pull out of crimps, boot lace ferrels and cause all sorts of hard to find intermittent faults.

 

[Lenny HB]

All this crimping going on, does anyone have their crimpers calibrated?

My old company used to supply calibration certificates for the crimpers used in control panels supplied to certain industries.

I have seen a few poorly crimped cables pull out of crimps, boot lace ferrels and cause all sorts of hard to find intermittent faults.

Never known a company do that but can understand the reason if manufacturing equipment for military, aircraft etc.

A good tug is normally a good test for DIY.
A DIY problem is people are frightened to tug too hard incase the joint fails, which of course the completely the wrong approach.

A cable should always be cut long enough to allow at least 2 remakes of the joint.

 

[tinkertaylor]

Never known a company do that but can understand the reason if manufacturing equipment for military, aircraft etc.

A good tug is normally a good test for DIY.
A DIY problem is people are frightened to tug too hard incase the joint fails, which of course the completely the wrong approach.

A cable should always be cut long enough to allow at least 2 remakes of the joint.

It's common practice for panel wiring, most quality crimpers will come with a 12 month certificate from new. Control panels can have 1000's of connections it's vital that they are quality assured. Imagine if one out of spec crimper is used to make these connections, the whole panel is useless, and could cause huge problems. Same as a high current connection on a low voltage system, huge fire risk.

Good idea on a pull test, the bigger the cable the harder the pull.

 

[Raul]

Pull test is at least that you can do on any crips, most hydraulic crimps with dissimilar sizes you can add strands to fill the lug, and do a second crimp with a size down dye. The crimps that I don't trust are hammer type crimpers, they just deform and squeeze the lug to grab the strands. Hydraulic, even chinese poor calibrated dyes can make a good cold weld if you practice enough, and understand the tool and parts you are using. Flared lugs with long barrel are my favourite as they can accommodate 2 or more dye withs, making the crimp longer than the dye with.
Pull test its not the best test, but is at least we can do, you could measure the resistance if you have the equipment.

 

[EuroTrotters]

buy 2 x batteries.

If you sell, you can tale one out.

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