Lithium battery conversion

[geem]

I did on my first LFP build but with my latest with EVE packs I have not bothered. All the negatives are at the same length from all the packs and all the positives are the same length from all the packs (to the mm) but the pos and neg are not the same as each other and it seems to make absolutely no difference to anything . When you think most people have things like a shunt in the neg circuit anyway which either adds length or resistance or has some other minute effect I think its more a broad stroke piece of advice from the old days .

I try to get my NH fuses as close to the battery positive terminal as I can. ABYC suggest 7" but the best I could do was 10". To compensate for the extra length they recommend sleaving the positive wire. I ran it in some red hose to maintain the colour coding of the positive wire and this gives good mechanical protection against chafe etc.
I don't worry about slight differences in cable lengths on each battery. I do have shunts on each battery. This is so that in the event of a battery failure, I can programme either shunt to be the control for solar charging. If you isolate the battery with the shunt connected and you have linked your mppts to that shunt for voltage information, the mppts keep charging as they read the wrong voltage. You could just disconnect the shunt and let the mppts sense their own voltage in an emergency but it was interesting have the shunt on each battery to see what was going on as well

 

[gregcope]

I wonder how much it really matters to keep the main +ve and -ve runs the same lengths? LFP has a very flat voltage curve so there will be minimal difference between the batteries unless you are in the top or bottom 5% of SOC, which isn't somewhere your batteries should spend any time.

People have paralleled up vastly different LFP capacities, and in hybrid systems put them together with a different chemistry entirely, and it doesn't seem to cause any problems.

Perhaps the requirement to keep the runs the same length is a hangover from best practice with lead acid?

Depends if you want to cycle different packs equally. If there is a (large) delta this may not be a concern. Over time it could become problematic… YMMV.

 

[gregcope]

I did the same as @geem and sleeved my battery tails to the fuse. My runs are about 600mm (24”?). 7” feels like its literally next to the battery which in my case was not possible. My wires inside the pack are also sleeved and secured as I did not want any surprises

I intend to open my packs this year to inspect as they are three years old.

 

[Daverw]

I’m fitting 2x200ah batteries, about 1500mm from buss bars, existing wiring to AGMs is 25mm, looking at 35mm cable to new with 150A T fuses each, one of the suggestions I’ve had is to go to 50mm cable, is that over the top for my short run? I’m going to sleeve individually in kopex to protect, may struggle to get fuses near batteries that can be easily accessible though

 

[gregcope]

@Daverw what Amps capacity is your BMS/battery?

150A fuses implies 100A draw from each.

 

[Daverw]

I’ve 2 off Victron 12.8v 200ah Smart Lithium, data sheet lists 400amp max, less than 200amp recommended. They have an external BMS controller but main boards are inside each batteries, cannot find more details of them.
My biggest load is Multiplus 1600w with others just normal house loads

 

[PaulRainbow]

I’ve 2 off Victron 12.8v 200ah Smart Lithium, data sheet lists 400amp max, less than 200amp recommended. They have an external BMS controller but main boards are inside each batteries, cannot find more details of them.
My biggest load is Multiplus 1600w with others just normal house loads

You need to use 50mm cable, because of the inverter (and the cables need to be less than 5m). A 150a fuse is not big enough, the inverter can draw 160a continuously and peak power up to 280a, fit a 300a fuse.

So, 50mm positive cable from the batteries to the 300a fuse, fuse to busbar, busbar to inverter. From the busbar to the rest of the domestics you can step the cable down and fuse accordingly.

50mm negative cable all the way from the batteries to the negative busbar, 50mm to the inverter and again, step down for the rest of the domestics.

No need for class T fuses, NH fuses are fine.

 

[Daverw]

Paul, that’s great info, assume you mean 50mm to each battery?
Just another question, what do you use for battery isolation, the ones I have planned to use appear to be rated at 200amp continuous

 

[PaulRainbow]

Paul, that’s great info, assume you mean 50mm to each battery?

Yes, treat each battery separately. So 50mm cables as above, from each battery. Keep the positive run of cables the same length as each other from each battery and the negative run the same from each battery.

Just another question, what do you use for battery isolation, the ones I have planned to use appear to be rated at 200amp continuous

There are some rated at more if you look on Google Dave.

 

[noelex]

Paul, that’s great info, assume you mean 50mm to each battery?
Just another question, what do you use for battery isolation, the ones I have planned to use appear to be rated at 200amp continuous

Blue Seas make several battery switches with a higher rating:

The m-series has a 300 Amp continuous rating.
The e-series has a 350 Amp continuous rating.
The HD-series has a 600 Amp continuous rating.
Or you can use their remote ML battery switch with a 500 Amp continuous rating.

It is time consuming, but important to ensure every component in the major current path can handle the maximum current limit imposed by the fuse. This includes battery switches, bus bars, cable lugs etc, as well as the cable itself (and I agree with Paul, you should use 50 mm square wire).

 

[rogerthebodger]

This is all interesting info

as for battery wiring, I tend to use 50sqmm welding cable with ring lugs fitted either by crimp or sometimes solder.

I know solder is not liked very well but on large able what does the forum think is you cannot get a good crimp.

 

[Sea Change]

This is all interesting info

as for battery wiring, I tend to use 50sqmm welding cable with ring lugs fitted either by crimp or sometimes solder.

I know solder is not liked very well but on large able what does the forum think is you cannot get a good crimp.

Solder isn't good for anything that may be subject to vibration. If you can't get a good crimp... buy better lugs.

 

[Daverw]

Blue Seas make several battery switches with a higher rating:

The m-series has a 300 Amp continuous rating.
The e-series has a 350 Amp continuous rat
The HD-series has a 600 Amp continuous rating.
Or you can use their remote ML battery switch with a 500 Amp continuous rating.

It is time consuming, but important to ensure every component in the major current path can handle the maximum current limit imposed by the fuse. This includes battery switches, bus bars, cable lugs etc, as well as the cable itself (and I agree with Paul, you should use 50 mm square wire).

Well I think I’m starting to get there, thanks to all.
Just found nh fuse holders, used but good, just need to order 400amp fuses and fuse extractor/ handle and decide on isolator switches

 

[Daverw]

Well battery switch’s, what a mine field, found many quoting high amps but when you look more closely they are not quoting continuous rating, also found some that had full 600amp spec but were about the same physical size as 100 amp ones, not sure if this avpctuslly works when you then look at the Bluesea HD range and their size.
Decided to go for Bluesea as I trust their spec,we’re out of stock in most but eventually found two, at least cable and lugs will be easy.

Note to others going this route, cabling cost are significantly higher than I planned, switches and fuses alone are coming to over £400

 

[Daverw]

Sorry to OP if I seem to be hogging this but I think the questions are useful to the thread,
Recommend are NH fuses, why is this? ANL fuse from Bluesea and Victron cover the required rating and holders are inclosed and not open form like NH

 

[noelex]

Recommend are NH fuses, why is this? ANL fuse from Bluesea and Victron cover the required rating and holders are inclosed and not open form like NH

The issue is ensuring the circuit has sufficiently high interrupt current (IC) protection. If the fuse has a lower IC than the battery is capable of delivering, in a short circuit situation the fuse can melt closed and therefore not break the current, as it should do.

Another way of looking at the specification is that the fuse rating (say 300 A) is the minimum current that the fuse will cut the current and the IC rating (say 10,000 A) is the maximum current where the fuse can cut the current.

Lithium battery banks can briefly deliver very high currents in a short circuit situation. It is therefore felt that for lithium banks, particularly larger banks that are often fitted to boats, need a main fuse with a IC rating of around 20,000 A (or higher). This requirement is not met by ANL fuses (or other common boat fuses). Most boats fit a T class fuse (excellent but expensive) or the cheaper NH fuses to overcome this issue.

T class fuse holders are enclosed, they have a very similar form factor to ANL fuse holders although the bolt hole spacing is different, so unfortunately they are not interchangeable.

 

[Daverw]

That’s really useful, just need to now revisit the NH fuses alone carriers I’ve just bought as I’ve found out since there are 3 fuses sizes, I’ve bought size 1 but these only fit up to 350amp, so need to get size 2 which are harder to find used, then need to find way of protecting them when fitted

Or down rate to 350amp which may be option

 

[PaulRainbow]

That’s really useful, just need to now revisit the NH fuses alone carriers I’ve just bought as I’ve found out since there are 3 fuses sizes, I’ve bought size 1 but these only fit up to 350amp, so need to get size 2 which are harder to find used, then need to find way of protecting them when fitted

Or down rate to 350amp which may be option

Why are you fitting such big fuses ? 50mm cable is only rated at 345a.

 

[Daverw]

Paul, I’m not sure where the 400amp came from but I wrote it down and it sort of stuck, you said in your earlier post 300amp and I never noted that. So the fuse holders I’ve got coming will do fine with NH1 size 300amp fuses, got bluesea battery switches coming Monday, just been hunting shed and boat for cable, lots of 35mm and 25mm but no 50mm so back to order some

 

[PaulRainbow]

Paul, I’m not sure where the 400amp came from but I wrote it down and it sort of stuck, you said in your earlier post 300amp and I never noted that. So the fuse holders I’ve got coming will do fine with NH1 size 300amp fuses, got bluesea battery switches coming Monday, just been hunting shed and boat for cable, lots of 35mm and 25mm but no 50mm so back to order some

Yes, 300a will be fine Dave. If you have enough 25mm cable you could use 2 x 25mm, as long as you keep each wire in a pair equal lengths. But, if it's just some old cable, best to get new 50mm.