Lithium fusing......

[ean_p]

I know that in the US a T class fuse is the recommended fuse for 'short' protection on a Lithium battery but looking at the curves I wonder what parameters other Lithium users have applied when it comes to selecting the rating of the fuse?
IE say for example 100ah battery which when used on an inverter may see 1.5C discharge therefore maybe a 150a T class fuse would be selected but that fuse might easily carry 300/400+ amps for several minutes thereby jeopardising the cabling connected to the battery. A sustained though possibly damaging discharge of 3C is not beyond question. Or is the approach a second in line fuse protective to the cable that may well be breached in the event of a direct short across the battery ?
Or is this all tosh thinking?

 

[andsarkit]

Are you protecting the battery or the cables?
The battery manufacturer can probably advise on the correct fusing for the battery.
From the Blueseas website:

If you are designing for an extended current draw a 100AT fuse would allow up to 150A for an extended period. You can always increase cable size if it is marginal.
Note that fuses are specified at an ambient temperature (often 25deg C) so can rupture at a lower current if the ambient is higher.
A short is likely to involve sparks and welding and a much higher current which will rupture the fuse quickly.
You can get fast fuses but these are usually only used for protection of semiconductors.
There are also thermal magnetic trips that combine a slow response to a small overload and fast response to a large overload.

 

[noelex]

The main reason a T class fuse is recommended, or in some cases mandated, is the high IC (interrupt capacity) rating of the fuse.

Personally, on a lithium system I would always use a T class fuse or other fuse type with a similar high IC rating (HRC fuses are also popular), but for a very small lithium system such as single 100Ahr battery it could be argued that a fuse with a lower IC rating such as ANL fuse may be acceptable.

If using a fuse with a lower IC rating you need to be confident that this rating is higher than the current the battery bank is capable of delivering. This can be hard to estimate so using a fuse type with the highest IC is wise.

The fuse rating is dictated by the wire size it is protecting. If you follow the guidelines you will be fine. There is no need to worry about the trip characteristics for most fuse types. However note that the maximium fuse size is influced by factors such as the temperature rating of the wire, whether or not it is bundled and if it passes through the engine room.

 

[Pete7]

Bimble solar do a range of NH fuses which might be worth a look. We have used their 160A version.

DC Fused Disconnect 1-pole NH1 fuse size, M10 fixings, 250ADC max

We also have a Blue Seas 150A circuit breaker for the inverter:

https://www.amazon.co.uk/dp/B000MMFJK2?ref=ppx_yo2ov_dt_b_product_details&th=1

The maximum draw we have seen is 115A when using the Ninja air fryer, but normally use other options in the 70A range.

 

[mattonthesea]

I know this might sound a daft question but here goes:
I am entertaining the idea of a 2kW inverter for an induction hob from the lithium batteries. Using W=VxA then the fuse and wire from batteries to inverter should be capable of carrying 170A for prolonged period. 25mm² min?

 

[Kelpie]

I know this might sound a daft question but here goes:
I am entertaining the idea of a 2kW inverter for an induction hob from the lithium batteries. Using W=VxA then the fuse and wire from batteries to inverter should be capable of carrying 170A for prolonged period. 25mm² min?

The cable may be rated at 170A but personally there's no way I would go that small. There's no margin for error and the voltage drop is likely to be substantial.
How short can you make the run?
For reference, I use 70mm² with a run of less than 1m, and I have the BMS set to cut off above 180A. I still find the cables can get warm after heavy use.

 

[PaulRainbow]

I know this might sound a daft question but here goes:
I am entertaining the idea of a 2kW inverter for an induction hob from the lithium batteries. Using W=VxA then the fuse and wire from batteries to inverter should be capable of carrying 170A for prolonged period. 25mm² min?

Depends how long the cables would be.

Depending upon the inverter, a 2kw model would draw about 200a at max continuous output, could be much more for a short period.

25mm sounds minimal, as does a 170a fuse.

 

[geem]

The cable may be rated at 170A but personally there's no way I would go that small. There's no margin for error and the voltage drop is likely to be substantial.
How short can you make the run?
For reference, I use 70mm² with a run of less than 1m, and I have the BMS set to cut off above 180A. I still find the cables can get warm after heavy use.

We are using 35mm2 on maximum load of about 100A. They get warm. No more than 1m. Very similar experience.
No way would I use 25mm2 cable for 170A

 

[mattonthesea]

Thanks Kelpie, Paul, Geem. I should have wired/fused appropriately to the bus bar on lithium installation. Proper planning etc! It will be next year now as our post B word 90 days is nearly up.

 

[PaulRainbow]

We are using 35mm2 on maximum load of about 100A. They get warm. No more than 1m. Very similar experience.
No way would I use 25mm2 cable for 170A

Is that 35mm @ 12v or @24v ?

 

[Trident]

Is that 35mm @ 12v or @24v ?

He's on 24v hence a 100A max on a 2kw inverter
In retrospect I wish I'd done a 24v bank just for the inverter as I have 120mm cable for a 3kw after the 90mm got hot to the touch

 

[Kelpie]

He's on 24v hence a 100A max on a 2kw inverter
In retrospect I wish I'd done a 24v bank just for the inverter as I have 120mm cable for a 3kw after the 90mm got hot to the touch

I considered 24v but obviously you need to be buying eight cells so the whole project gets much more expensive.
I never thought we would end up cooking 95% on electric on a system that cost less than £1k to put together. If I'd known how well it was going to work I would have built a bigger system.

 

[geem]

Is that 35mm @ 12v or @24v ?

Yes,24v.
I think with running lithium, 24v has lots of advantage. Halving BMS loads is the major one. A lot smaller cable sizes and being able to run normal domestic induction cookers with no problem

 

[PaulRainbow]

Yes,24v.
I think with running lithium, 24v has lots of advantage. Halving BMS loads is the major one. A lot smaller cable sizes and being able to run normal domestic induction cookers with no problem

Thought you were 24v (at least tome systems).

My boat is primarily 24v, with a few systems running on 12v through DC-DC converters, LED lights being one such system, much more stable than running them on 24v where voltages can be much higher than 24v.

I'm about to fit a 3kw Power Star inverter, in part due to your positive comments about them. I usually fit Victron, but at 3 times the cost of the Power Star i'm going to give it a go. Will be 35mm cables too.

 

[geem]

Thought you were 24v (at least tome systems).

My boat is primarily 24v, with a few systems running on 12v through DC-DC converters, LED lights being one such system, much more stable than running them on 24v where voltages can be much higher than 24v.

I'm about to fit a 3kw Power Star inverter, in part due to your positive comments about them. I usually fit Victron, but at 3 times the cost of the Power Star i'm going to give it a go. Will be 35mm cables too.

Efficiency of LEDs depends on the type you are running. Mine are predominantly designed to run at 9-30v. They use electronic controls. This type is more energy efficient closer to 30v than 9v. Many have been installed since I bought the boat in 2012. They have proved to be super reliable and energy efficient.
If you are using dimmable LEDs they are more reliable at lower voltages.as you say.
The Power Star low frequency inverters are great. Very happy with ours

 

[Pete7]

Thanks Kelpie, Paul, Geem. I should have wired/fused appropriately to the bus bar on lithium installation. Proper planning etc! It will be next year now as our post B word 90 days is nearly up.

Buy the induction hob and use it at home first. I think you will be pleasantly surprised how little power you actually need to cook with induction. We tend to sear steaks at 1000w and then turn down or risk turning them into charcoal. Bacon say 600w, simmering pasta or new potatoes say 200w, but we use a lid which helps too. The hob is a 1500w Sterling, but we never need to use full power. The displayed figures are more of an average rather than actual figures.

The inverter is 2kW and 25mm wire. This did get warm with the air fryer at 1500w so replaced the wiring with 35mm. No problem since. Wire run is about 2m including the return. This isn't to say you shouldn't use the appropriate size for the demand or future use, like a vacuum cleaner which tend to be quite high demand.

 

[Kelpie]

Are you 12 or 24v?

 

[geem]

Buy the induction hob and use it at home first. I think you will be pleasantly surprised how little power you actually need to cook with induction. We tend to sear steaks at 1000w and then turn down or risk turning them into charcoal. Bacon say 600w, simmering pasta or new potatoes say 200w, but we use a lid which helps too. The hob is a 1500w Sterling, but we never need to use full power. The displayed figures are more of an average rather than actual figures.

The inverter is 2kW and 25mm wire did get warm with the air fryer at 1500w so replaced the wiring with 35mm. No problem since. Wire run is about 2m including the return. This isn't to say you shouldn't use the appropriate size for the demand or future use, like a vacuum cleaner which tend to be quite high demand.

Our induction hob is 2000w. From power settings from 1000-2000w, it goes in 200w steps. Each step matches the power on our energy meter.
Below 1000w the power steps are pulsed so these aren't the actual power of the setting, just an average.
The higher settings are great for boiling the kettle or brings pans to the boil fast. If you are boiling the kettle, with 2000w instead of 1500w, you don't use any more energy with a 2000w hob than a 1500w hob. The 1500w hob just takes longer. If your system can take the higher induction hob loads, then why not?
A boat wired for 24v has no issue with the higher hob rating as for the same lithium BMS, we run it at half the amps.
Our induction hob cost £26 from Aldi about 15 years ago. In tests online, it's still rated as the best portable single ring, induction hob.

Our vacuum cleaner is a shop vac from Toolstation. 700w

 

[Pete7]

Are you 12 or 24v?

12v boat, well 13v with those dilithium crystals. The kettle is 1kW which we prefer to boil water.

 

[Pete7]

Our vacuum cleaner is a shop vac from Toolstation. 700w

Perfect.

I think the take home from this thread is you don't need lots of blue boxes. Also it pays to think about what you intend to use. For example at home the kettle is 2kW. On the boat the little Argos kettle is just 0.8L. Half full is the perfect amount for two mugs of tea, so saves boiling more than needed as does cooking with lids which also helps keep the condensation down and the heat in the pan.

We did look at electric convention ovens running at 1500w and then bought this. At 580w brilliant for cooking and baking.

Pete