Seplos Mason - advice on terminal fuse and DC isolation switch

[turnipface]

Hello all

I am trying to work out the safest way to connect a Seplos Mason 280L vertical 48V DIY kit to a Solis S5-EH1P6K-L hybrid inverter. Please could I seek the expertise of the forum on my plans - please correct me if any of the following is wrong/could be safer!

1. The max charge / discharge current of the S5-EH1P6K-L is 100A. Fuses should be rated to 125% of the max current, so 125A.

2. A MRBF terminal fuse is slightly better than a class T fuse as it is closer to the battery and results in fewer connection points, so less heat buildup.

3. Assuming 1 and 2 are correct, I was looking at purchasing the following:

Blue Sea Systems MRBF Terminal Fuses

Space saving MRBF fuses for high current circuits such as main battery feed, inverter, windlass, bow thruster, etc. 30-300A ratings & high interrupt capacity.

www.12voltplanet.co.uk

Blue Sea Systems 5191 MRBF Terminal Fuse Block 30-300A

Space-saving, ingition-protected MRBF 5191 fuse block for high amperage circuits such as DC main feed, inverter, windlass, bow thruster etc. 58VDC, 300A rated.

www.12voltplanet.co.uk

Would these be suitable?

4. The fuse will be connected to the positive terminal of the Seplos battery.

5. Between the fuse and the inverter I should have an isolation switch. This one looked appropriate:

Victron Energy Battery Switch On/Off 275A

This Victron 275A battery switch can be used to isolate DC loads and/or DC charging sources in systems up to 48V DC in vehicles, boats & off-grid applications.

www.12voltplanet.co.uk

6. The battery cable that came with the inverter will connect the inverter to the isolation switch. I will then need another cable to connect the isolation switch to the fuse on the Seplos battery positive terminal. The fatter and shorter the better. This looked appropriate without being overkill on cross-section size:

Oceanflex Extra Flexible PVC Tinned Battery Lead With 8mm Terminals - Red 35mm² 240A

Oceanflex extra flexible battery leads manufactured from PVC-sheathed cable with tinned copper conductors. Corrosion resistant for use in marine environments.

www.12voltplanet.co.uk

All thoughts greatly welcome!

 

[SeaGal]

Hello all

I am trying to work out the safest way to connect a Seplos Mason 280L vertical 48V DIY kit to a Solis S5-EH1P6K-L hybrid inverter. Please could I seek the expertise of the forum on my plans - please correct me if any of the following is wrong/could be safer!

I'll have a stab...

1. The max charge / discharge current of the S5-EH1P6K-L is 100A. Fuses should be rated to 125% of the max current, so 125A.

, sort of. Fuses protect wires. So first ensure that your wires can safely handle at least 125% of the max current, ideally more. And make sure that the fuse is rated lower than the wires can carry. So, my rule of thumb is add 25% over max current for the fuse and another 25% above the fuse for the wire.

2. A MRBF terminal fuse is slightly better than a class T fuse as it is closer to the battery and results in fewer connection points, so less heat buildup.

No. MRBF is not as good as class T.

But class T fuses are expensive in the UK. I'd recommend NH class fuses myself, but I must admit the concept of the connection point of the MRBF is appealing. See also this thread re testing of MRBF and the slow-mo video on the first posting...
https://diysolarforum.com/threads/dead-short-fuse-trip-experiment-using-an-mrbf-fuse.80773/

4. The fuse will be connected to the positive terminal of the Seplos battery.

5. Between the fuse and the inverter I should have an isolation switch. This one looked appropriate:

Victron Energy Battery Switch On/Off 275A

This Victron 275A battery switch can be used to isolate DC loads and/or DC charging sources in systems up to 48V DC in vehicles, boats & off-grid applications.

www.12voltplanet.co.uk

No. It is only rated to 48v and you will be running up to about 56V. It is also only a single pole isolator.

I'd recommend using a dual pole fused isolator, like one of these that can be fitted with 125A NH00 class fuse.
https://essandsolarsolutions.co.uk/jean-muller-combined-keto-00-fuse-holder-and-battery-disconnect/

6. The battery cable that came with the inverter will connect the inverter to the isolation switch. I will then need another cable to connect the isolation switch to the fuse on the Seplos battery positive terminal. The fatter and shorter the better. This looked appropriate without being overkill on cross-section size:

Oceanflex Extra Flexible PVC Tinned Battery Lead With 8mm Terminals - Red 35mm² 240A

Oceanflex extra flexible battery leads manufactured from PVC-sheathed cable with tinned copper conductors. Corrosion resistant for use in marine environments.

www.12voltplanet.co.uk

IMHO 35mm2 is ideal for further connections (and bigger than the ones Solis supply) - the M8 terminals will fit the isolator I linked to if you go down that route too.

All thoughts greatly welcome!

Part of this thread around my posting linked below may be of interest too..

Post in thread 'Inverters that support high voltage (500v) storage batteries'

Oct 4, 2024

My rule of thumb is that the fuse should be rated 25% greater than your regular expected usage and the cable rated 25% above the fuse. Fuse must always be less than cable rating.

Now just to find which 00 switch holder/disconnector to choose. Want to find a quality one but reasonably priced.

IME, I'd look at Mersen, ABB, Eaton and Jean-Muller.

MERSEN | NH fuses and fusegear

Mersen is a leader in the protection of DIN systems. Our product encompasses a complete range of NH Switch Fuse Disconnector's and any class of NH power fuses : gG, aM, gTr. These devices must be handled by a qualified professional. Visit Electrical Power website

www.mersen.co.uk

P1023007 / 2.030.000 | Mersen 160A Rail Mount Fuse Holder for 00 Fuse, 3P, 690V ac | RS

uk.rs-online.com

...

• SeaGal

• 

 

[turnipface]

Thanks for those replies, that is all very helpful. The idea of combining the fuse with the isolator is very appealing as it reduces the amount of work to install, but, having read this thread and its recommendations for class T fuses above all else, I just wanted to check why you recommend a NH00 fuse instead? I don't mind spending ~£120 on a class T fuse and fuse holder if that's the safest option.

 

[SeaGal]

I just wanted to check why you recommend a NH00 fuse instead? I don't mind spending ~£120 on a class T fuse and fuse holder if that's the safest option.

For availability and price trade-off reasons, in UK.

I guess a Hummer would be safer to drive than my VW EV, but an overkill IMHO

BS88 is also an option.

But... I'm only an electronic engineer... I'll let @upnorthandpersonal chip in as he's the expert on these matters if £££ is no issue.

 

[upnorthandpersonal]

When looking for a fuse to couple with a 48V LFP pack, you're really trying to satisfy these criteria:

- Fast acting: in case something goes wrong, you want to disconnect as soon as possible. This is in contrast to fuses that are coupled to e.g. motors, since these are not supposed to act very quick due to expected large sure currents on start.

- High Breaking capacity (IR, interrupt rating): a short can produce thousands of amps, you need a fuse that can deal with that.

There is another reason you want a fast acting fuse: in the old days, the saying went "fuses protect wiring, not equipment". This is not 100% correct anymore, since we use fuses to protect things like inverters, and size the fuse based on the maximum current that device should ever see, not based on the wires it's connected with. Same goes for things like the BMS. These are essentially fast acting fuses specifically with this in mind, and are called semiconductor fuses (they contain a diode in their symbol to indicate this).

There are entire subcategories when it comes to fuses. We have things like aR, gBAT, gG, etc. A gG fuse is general purpose, but slower than an aR fuse. However aR fuses tend to have more losses associated with them. It's a bit of a trade-off.

Class-T, as well as BS-88 and NH style fuses (you still have to check: NH fuses can be gG as well, it's just a form factor but they have dedicated gBAT fuses in this form factor as well), contain fuses that provide a balance in this trade-off. They're fast acting, have a high interrupt rating, and are suitable for device protection while minimizing losses.

Class T used to be readily available even in Europe, but these days they're hard to find and have become expensive. I personally use BS-88 fuses on the battery packs since they have a similar-ish form factor to Class T (i.e.m they're rather small), compared to an NH style fuse which are much bigger. I use the NH fuses on the inverters.

In the end, it comes down to checking the datasheet of the fuse you have in mind and make sure it has the required breaking capacity, usable for your application (DC, voltage range, fast acting) and at a decent price point.

 

[turnipface]

Thank you both, I hadn't managed to find this information presented like this anywhere else, so it is all extremely useful. I'll do some more research and probably come back with more questions. One immediate question - you mentioned fusing the inverter - is a separate fuse needed/recommended for the inverter? Or does the fuse between the battery and the inverter do the job of protecting both?

 

[upnorthandpersonal]

is a separate fuse needed/recommended for the inverter?

Separate fuse is recommended, and in most cases required. For example assume you have a 5kW inverter and two 48V batteries in parallel powering that. Even with just a 100A BMS, the combined batteries can deliver 200A (10kW) without their 125A fuses blowing (each pack in parallel needs a fuse). If the 5kW inverter draws 10kW (except for short periods of surge) something is wrong, so the inverter also needs a 125A fuse.