Fuse HOW ?*!? much? Is there an alternative?

[Odana]

When John was doing the fan belt last week he accidentally caught summat he shouldn't have with a spanner and blew the main in line fuse from the battery bank.

 

We have searched by part number for this item and found it in various places for !!!!!EIGHTY QUID!!!! give or take a fiver. It is an A3T300 and looks like this http://www.tizaro.com/product/EL2BK9/ferraz-shawmut-a3t300-fuse-a3t-300vac-160vdc-300a-fast.

 

There are other 300 A fuses available for under a fiver, such as this one http://www.ebay.co.uk/itm/MEGA-fuse-300-Amp-300A-Automotive-Marine-fuse-/140775256425.

 

So, what does this mega-fuse thingummy do that's worth eighty quid and can we replace it with something less eye-watering? If so, what?

 

 

If it helps we have 4 150A traction batteries and a Victron all-singing-all-dancing unit. At present the 12v will run through the victron while we're on a landline, but otherwise not. And it keeps dying. Batteries are OK.

 

Thanks for any help!

 

 

[Paul C]

At first appearance, seems to be fast blowing. AFAIK fuse blow time is inversely proportional to the current over its rating. Ie if you have a 300A fuse and flow a 301A current, it would take ages to blow. But put a 1000A current through and it would blow quickly.

 

What circuit is it protecting, ie which battery bank and is the alternator and starter motor also in the circuit or separate?

[frangar]

Google class t 300a fuses

 

Cheers

 

Gareth

[Richard10002]

http://www.amazon.co.uk/Blue-Sea-Systems-Class-Fuse/dp/B000XBGT3S

 

3 left. £30

[steelaway]

Try here ----http://www.ebay.co.uk/sch/i.html?_trksid=p3984.m570.l1313.TR0.TRC0&_nkw=+t+300a+fuses&_sacat=0&_from=R40

 

 

Alex

[Chris Pink]

So what do you get for £30 in a class T fuse that you don't in a £5 Littel mega fuse?

[Timleech]

So what do you get for £30 in a class T fuse that you don't in a £5 Littel mega fuse?

 

They are supposed to be very fast blowing, to protect electronic equipment, recommended by some for inverter supplies.

If you believe our late friend Gibbo, they won't help to save very much. If electronics are going to fry, they will fry anyway (I paraphrase).

Make your own judgement.

 

Tim

[Paul C]

They are supposed to be very fast blowing, to protect electronic equipment, recommended by some for inverter supplies.

If you believe our late friend Gibbo, they won't help to save very much. If electronics are going to fry, they will fry anyway (I paraphrase).

Make your own judgement.

 

Tim

 

Yeah, fast blowing but its kinda tied in with the current required to blow it too. For example, if a normal fuse passed 305A for 3 secs, might not blow at all. A fast blowing one would. Basically it more precisely blows at the rated current.

[Odana]

At first appearance, seems to be fast blowing. AFAIK fuse blow time is inversely proportional to the current over its rating. Ie if you have a 300A fuse and flow a 301A current, it would take ages to blow. But put a 1000A current through and it would blow quickly.

 

What circuit is it protecting, ie which battery bank and is the alternator and starter motor also in the circuit or separate?

Apparently it goes into the Victron unit. If he blew it with a spanner touching the alternator live, I assume the alternator is in the circuit too? I haven't looked since this morning before he found the fault. So if there is expensive kit to be saved, I am happier to spend 30 quid. Though it seems a basic fuse might be fine, why risk it. May get a cheap one for future emergencies though - if we were out away from land line we'd be very grumpy right now.

 

Edited to add - damn, this forum's good!! 30 mins from head-scratching to reassurance AND some shopping links. Thanks all. Amazon it is.

Edited May 25, 2013 by Odana

[Paul C]

I was just thinking, why have a posh fuse at all, why not just use an appropriately rated bog standard megafuse.

[Odana]

The fast-blowing thing makes sense if there is sensitive kit to be protected. But yes, a £299 fuse is tempting

Next question from John here- how does one put this new expensive bit of kit on without it sparking and blowing. I said isolate the batteries but apparently he thinks there's more to it than that

[nicknorman]

The fast-blowing thing makes sense if there is sensitive kit to be protected. But yes, a £299 fuse is tempting

Next question from John here- how does one put this new expensive bit of kit on without it sparking and blowing. I said isolate the batteries but apparently he thinks there's more to it than that

However it seems unlikely that it blew to protect the inverter - it blew to protect the wiring between battery and alternator and/or inverter. The inverter charger isn't able to produce 300A. But OK £30 might be worth it for your peace of mind rather than for any scientific reason!

 

If the fuse is protecting a direct connection between the inverter and batteries (not through the isolator) then its going to spark a bit when its connected as the inverter capacitor(s) charge up. However this shouldn't blow the fuse as the I^2t integral is too small (ie not enough energy) - after all it had to be connected originally and that didn't blow the fuse.

Edited May 25, 2013 by nicknorman

[steelaway]

As sold/recomended by Sterling Power Products -------------- http://www.shop.sterling-power.com/cgi-bin/sh000003.pl?REFPAGE=http%3a%2f%2fwww%2eshop%2esterling-power%2ecom%2facatalog%2fshop%2ehtml&WD=fuse&PN=ANL_fuses%2ehtml%23a1_21GANL300A#a1_21GANL300A

 

Alex

[Timleech]

I was just thinking, why have a posh fuse at all, why not just use an appropriately rated bog standard megafuse.

 

One reason may be that a megafuse will probably not fit the holder. Mind you, a megafuse holder is probably only a few quid.

 

Tim

[Chalky]

However it seems unlikely that it blew to protect the inverter - it blew to protect the wiring between battery and alternator and/or inverter. The inverter charger isn't able to produce 300A. But OK £30 might be worth it for your peace of mind rather than for any scientific reason!

 

The whole purpose of a fuse is to protect the wiring, not the electronics and as Gibbo said no fuse is going to act fast enough to protect power electronics.

 

Try Radio spares http://uk.rs-online.com/web/ or Farnell http://uk.farnell.com/ for the fuse. They're large industrial slectrical/electronics companies and should have stock.

[DaveC]

They are supposed to be very fast blowing, to protect electronic equipment, recommended by some for inverter supplies.

If you believe our late friend Gibbo, they won't help to save very much. If electronics are going to fry, they will fry anyway (I paraphrase).

Make your own judgement.

 

Tim

 

Is Gibbo late as in deceased?

 

 

Dave

[Arthur Brown]

"Next question from John here- how does one put this new expensive bit of kit on without it sparking and blowing. I said isolate the batteries but apparently he thinks there's more to it than that"

 

If the rest of the circuit is functioning correctly then isolate, fit fuse, tighten bolts and switch on.

 

Good advice would be to put insulation over the handle of the spanner. Maplin sell 1000v insulated screwdrivers but for 12 or 24v you could use gaffer tape or the finger off a rubber glove. cover the spanner right to the end. Look in B&Q for an insulated adjustable spanner. When near live contacts cover all rings and remove all jewellery

Edited May 26, 2013 by Arthur Brown

[Timleech]

Is Gibbo late as in deceased?

 

 

Dave

 

Late as in departed (from this forum).

 

Tim

[bottle]

The fast-blowing thing makes sense if there is sensitive kit to be protected. But yes, a £299 fuse is tempting

 

Next question from John here- how does one put this new expensive bit of kit on without it sparking and blowing. I said isolate the batteries but apparently he thinks there's more to it than that

 

Turn everything OFF.. There may still be a spark but it will only be a small one.

 

When putting the fuse on the studs do it with a determination, do not faff about.

[Bobbybass]

Late as in departed (from this forum).

 

Tim

That's good that he's not 'late' but not good as in departed.

 

I liked him.

 

Bob

[Guest]

Odana - I got a t_class fuse from Keith M who sometimes posts on here.

 

If you are at Crick and he is there this weekend he will be on his stand (Volt master).

 

From memory it was around £22. Try a PM to him.

[Keith M]

PM sent

 

Keith

[smileypete]

So what do you get for £30 in a class T fuse that you don't in a £5 Littel mega fuse?

 

Good question sir! What you get is a much higher 'breaking capacity'.

 

A mega fuse is actually only designed to interrupt up to about 2000A at rated voltage, whereas the Class T fuse is designed to interrupt up to 20kA or 20,000A. A large batt bank could easily put out way more than 2000A if shorted.

 

Begs the question, what happens if you pass say 10kA at though a mega fuse? Maybe behave unpredictably and arc or even disintegrate in in a spectacular way. Personally though I don't think it's likely to be a problem at 12V but don't hold me to it if it is

 

As for the cost of a Class T fuse, it seems that it's a mainly US standard which is why it's less common and often quite expensive. The nearest UK equivalent would be a BS88 HRC fuse, available in a wide range of current ratings and breaking capacities.

 

To try to get the best of everything I'd favour trying a hybrid approach, use the usual mega fuses or ANL fuses for protecting everything then have a HUGE HRC fuse to provide breaking capacity beyond 2000A

 

Then a short should just blow the mega fuse first (as it has a much lower I²T rating) but if not the HRC fuse is there as a backup. I'd also even consider putting the HRC fuse in the batt bank main negative, then it would protect against the typical bat post to hull with a spanner type shorts.

 

This sort of thing is a decent size for additional breaking capacity, bearing in mind it's a big, about 8" long, but gives breaking capacity up to 80kA

 

http://www.ebay.co.uk/itm/MEM-FUSE-LINK-80kA-415V-AC-800A-BS88-2-1988-LIST-NR-800SH10-/281056111426

 

cheers, Pete.

~smpt~

Edited May 26, 2013 by smileypete

[Radiomariner]

Good advice would be to put insulation over the handle of the spanner. Maplin sell 1000v insulated screwdrivers but for 12 or 24v you could use gaffer tape or the finger off a rubber glove. cover the spanner right to the end. Look in B&Q for an insulated adjustable spanner. When near live contacts cover all rings and remove all jewellery

Good advice, yes, but....

After job done, remove the temproary insulation. I would rather use a tool that I know is not insulated than rely on the insulation of one that is damaged. The next job for the insulated tool may be at much higher voltage!

I say this from experience, a properly insulated electricians pliers rated at 2000V very slightly damaged from being kept in a toolbox along with other tools with sharp edges, gave a real nasty hospitallisation shock to a workmate of mine, many years ago. Since then I always rigorously inspect insulated tools for damage to insulation and throw them out if suspect.

Sometimes the insulation can be removed and the tool still used for non electrical work.

[smileypete]

For doing up batt nuts a plastic handled T-bar with a socket on it might work better than a spanner, easy to slip some tubing over the shaft to insulate it.

 

cheers, Pete.

~smpt~