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DC FUSES


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Hi Guys

 

Take a look at the attached. These are DC fuses from ACDC dynamics.

May I use those DIN rail fuses as a 48V battery protection?

I see they have a High Voltage rating. Is this the max voltage? Is there a minimum voltage too?

Thanks Guys

post-121-0-73632800-1440765933_thumb.png

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Hi leaves

 

You can use those fuses - they will be perfect. The voltage rating is the maximum voltage the fuse will be able to isolate when it goes open circuit in case of a fault condition. They will be perfect for low voltage (48V) use.

 

If you are looking for 100A fuses or lower, you can use this fuse holder from ACDC: CMS2258.1 It is also a DIN rail mount fuse holder.

Fuses e.g. 100A: 2258.100

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  • 1 month later...

I've used a 100Amp fuseholder with fuse on my Axpert between the inverter and the batteries on the positive cable for 90 bucks incl and it works perfectly. You can source them from The Security Mecca Vereeniging 016-422-5667 or Potchefstroom 018-293-2103. Their product code is RENEW101.

 

 

 post-1131-0-47106800-1444048453_thumb.jp

post-1131-0-47106800-1444048453_thumb.jp

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I've used a 100Amp fuseholder with fuse on my Axpert between the inverter and the batteries on the positive cable for 90 bucks incl and it works perfectly. You can source them from The Security Mecca Vereeniging 016-422-5667 or Potchefstroom 018-293-2103. Their product code is RENEW101.

 

 

 post-1131-0-47106800-1444048453_thumb.jp

 

Those look like car amp fuse holders and fuses, rated for low voltages (12V?) - am I correct. Don't use automotive fuse holders and fuses for 48V battery systems - they are not designed for the higher voltages.

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Utilisation category:

AC-23A frequent switching of highly inductive loads

AC-23B occasional switching of highly inductive loads

DC-23A frequent switching of highly inductive loads (e.g. series motors)

DC-23B occasional switching of highly inductive loads (e.g. series motors)

 

DC -23A requires 2 poles in series.

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  • 1 month later...

Those look like car amp fuse holders and fuses, rated for low voltages (12V?) - am I correct. Don't use automotive fuse holders and fuses for 48V battery systems - they are not designed for the higher voltages.

Mmmmm.... care to elaborate, please?

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I think the issue is about the gap that is created when a fuse blows. If the gap is too small, the voltage can jump across. Thinking about this logically (or at least as much as I think I'm doing so), if you were to take a high speed video of a fuse blowing and play it back slowly, you will likely see that as the fuse blows, it starts with a small gap that then grows until it is large enough to stop the flow of current.

 

A fuse will therefore be designed for a particular voltage, and using a higher voltage means it might not open the gap quickly enough, so there might be enough time to heat and melt things you don't want heaten or molten... and from this point on you can go look on youtube what happens in those cases.

 

I would love a more in-depth explanation as to what happens. As I recall, rule of thumb, you need about 100V to jump a millimeter (that's if I recall correctly), so in theory you want a material that creates a millimeter of space very quickly.

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Mmmmm.... care to elaborate, please?

 

" they are not designed for the higher voltages."

 

The purpose of a fuse is to isolate a circuit in case of a fault condition, that is when the current flowing in the circuit is larger than the rating of the fuse. When a DC circuit is disconnected, e.g. in a switch, circuit breaker or fuse, while a high current is flowing in that circuit, it causes an arc. The higher the voltage between the two disconnected points, the bigger the arc will be and therefor the points where the circuit is disconnected, inside the switch, circuit breaker or fuse, needs to be further apart for higher voltage circuits in order to help to distinguish the arc. If you are using switches, circuit breakers and fuses with voltage ratings much lower than the voltage it needs to isolate, the arc will not be distinguished properly or soon enough and that might cause overheating, melting and possibly an explosion.

 

Edit: Plonky, you beat me to it with 1 minute.  :)

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" they are not designed for the higher voltages."

 

The purpose of a fuse is to isolate a circuit in case of a fault condition, that is when the current flowing in the circuit is larger than the rating of the fuse. When a DC circuit is disconnected, e.g. in a switch, circuit breaker or fuse, while a high current is flowing in that circuit, it causes an arc. The higher the voltage between the two disconnected points, the bigger the arc will be and therefor the points where the circuit is disconnected, inside the switch, circuit breaker or fuse, needs to be further apart for higher voltage circuits in order to help to distinguish the arc. If you are using switches, circuit breakers and fuses with voltage ratings much lower than the voltage it needs to isolate, the arc will not be distinguished properly or soon enough and that might cause overheating, melting and possibly an explosion.

 

Edit: Plonky, you beat me to it with 1 minut

 

" they are not designed for the higher voltages."

 

The purpose of a fuse is to isolate a circuit in case of a fault condition, that is when the current flowing in the circuit is larger than the rating of the fuse. When a DC circuit is disconnected, e.g. in a switch, circuit breaker or fuse, while a high current is flowing in that circuit, it causes an arc. The higher the voltage between the two disconnected points, the bigger the arc will be and therefor the points where the circuit is disconnected, inside the switch, circuit breaker or fuse, needs to be further apart for higher voltage circuits in order to help to distinguish the arc. If you are using switches, circuit breakers and fuses with voltage ratings much lower than the voltage it needs to isolate, the arc will not be distinguished properly or soon enough and that might cause overheating, melting and possibly an explosion.

 

Edit: Plonky, you beat me to it with 1 minute.  :)

Makes sense, thanks.

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  • 1 year later...

So i'm gonna resurrect this thread :) 

I'm really struggling to find inline DC Fuses... I want to add another string to my battery bank and lots of info on this forum is recommending that i fuse each string. I'm looking for a wall mountable fuse holder that can take 2 fuses. Any recommendations on products or a place i can contact? 

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I bought myself a Victron holder with a Mega-fuse for the last project. The fuse was expensive (there's a 32V one and an 80V one, price is significantly more for the 80V one), ... the holder wasn't that expensive. This one. It's a very common type of fuse and should be available from most solar places or online, but I got mine at OnTrack down the road (they stock most Victron stuff).

Sonop Solar has them too... but they are rather expensive compared to what I paid (and then you still need to ship them). I think I paid just over R200 for the fuse and the holder, if memory serves.

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So i called ACDC Express.... they have these available.

image.thumb.png.55ccbdc07fd2aba69935bb2b86cc9623.png

Fuse 24585-125A is R61 ex VAT

Fuse UF24585-125A is R216 ex Vat (Ultra fast, not sure what it means in real terms?)

Fuse Holder NL24585 - CT-00FB 1 Pole is R103 ex VAT...

Pricing is not too bad... I'm guessing the Ultra Fast are the ones i need to get? What do the experts reckon?

 

Then in terms of Busbars... would the below work?

image.thumb.png.9459bd3dd16e84b8f80df89326f93dad.png

 

 

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On 11/1/2017 at 2:24 PM, PurePower said:

I want to add another string to my battery bank and lots of info on this forum is recommending that i fuse each string.

You originally mentioned fusing of strings - this would typically be in the 10amp to 15amp range where the HRC (High Rupture Capacity) fuses would not be required, the fuses on the page that I attached in my previous reply is the correct item (order if necessary).

You could use HRC fuses for your Battery Bank Main and for your PV Array Main (after the string fuses in your combiner box) but I would recommend rather using DC circuit breaker in this instance.

The problem with fuses is that they blow, and when they do people typically replace the blown fuse with a nice fat blou-draad because a replacement is not close to hand - then if the fault has not been cleared your equipment is going to turn into a puff of smoke.

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3 hours ago, PurePower said:

I'm guessing the Ultra Fast are the ones i need to get?

Not necessarily. The normal ones usually don't blow immediately if you go over the limit. You can go over up to 20% for short periods (how long depends on how much) and it won't blow. That's usually sufficient when the fuse's job is to protect a cable, if you exceed the rating of the cable, the fuse will go long before the cable overheats.

The fast blow ones are when you want to protect equipment, things that get damaged quickly. Typically in circuits with power transistors, you want the fast-blow one, the idea being that the fuse blows faster than the transistor.

When replacing the fuse, using the wrong one either leads to nuisance blowing, or damage to the equipment.

You should watch Big Clive's presentation on the topic.

3 hours ago, PurePower said:

Then in terms of Busbars... would the below work?

Those busbars will work, but did you check the price? I looked at those too... I went down the road to Cronlec and got two earth bars. The post is here. That was significantly cheaper. I put them into a UT7 slide lid box along with the BMV shunt.

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3 hours ago, pilotfish said:

You originally mentioned fusing of strings - this would typically be in the 10amp to 15amp range where the HRC (High Rupture Capacity) fuses would not be required, the fuses on the page that I attached in my previous reply is the correct item (order if necessary).

You could use HRC fuses for your Battery Bank Main and for your PV Array Main (after the string fuses in your combiner box) but I would recommend rather using DC circuit breaker in this instance.

The problem with fuses is that they blow, and when they do people typically replace the blown fuse with a nice fat blou-draad because a replacement is not close to hand - then if the fault has not been cleared your equipment is going to turn into a puff of smoke.

 

Hmm...maybe i wasn't clear enough. I am following the guidelines from the document made available by @superdiy , thanks @superdiy

 

 

I currently have a Mersen 125A Fused Battery disconnect between the inverter and the single bank. With my plans of adding another string, i want to follow the diagram below.  

image.thumb.png.fab2b957e29ba8064f2f12de0ed4ef6c.png

image.png.f84a0b757e65c0146f06d3ddcd874186.png

 

When adding another string it recommends that you fuse (circled in green above) each string as per the snippet from the doc below. It is those fuses in question.

image.thumb.png.959ed106ac9c4c02c4b5cbe03b8eb453.png

I have the Axpert 5kva/4kw inverter. The max inverter current is 83.33A. My calculation as per above works out to 104A based on 2 strings. We don't get a 104A fuse, so we settle for a higher one that is available, 125A. So my understanding based on this info, the fuses i need to add to each string on the positive side should be 125A. 

What is confusing me is that it also mentions in the above paragraph that the fuse per string should be lower than the rating of the main battery fuse.... So if the calculation earlier works out to 125A per fuse, does this mean i need to get a higher rated fuse for the Mersen battery disconnect?

 

1 hour ago, plonkster said:

Not necessarily. The normal ones usually don't blow immediately if you go over the limit. You can go over up to 20% for short periods (how long depends on how much) and it won't blow. That's usually sufficient when the fuse's job is to protect a cable, if you exceed the rating of the cable, the fuse will go long before the cable overheats.

The fast blow ones are when you want to protect equipment, things that get damaged quickly. Typically in circuits with power transistors, you want the fast-blow one, the idea being that the fuse blows faster than the transistor.

When replacing the fuse, using the wrong one either leads to nuisance blowing, or damage to the equipment.

You should watch Big Clive's presentation on the topic.

Those busbars will work, but did you check the price? I looked at those too... I went down the road to Cronlec and got two earth bars. The post is here. That was significantly cheaper. I put them into a UT7 slide lid box along with the BMV shunt.

So to protect the inverter its better to use the fast ones. I'll keep some spares in case it blows, then i don't need to use a blou draad to temporarily keep it connected. 

As for the busbars, i'll check the price first then decide if i'll opt for the earth bars or not. Just a question, where should the BMV shunt be placed on the diagram above? Between the Mersen and the negative busbar?

Please comments on the above. 

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1 hour ago, PurePower said:

So to protect the inverter its better to use the fast ones.

The inverter has built-in fuses for that purpose, at least according to the manual. They still recommend that you put in overcurrent protection. It's up to you, I personally doubt that it makes much sense to spend extra money on the fast-blow fuses. When the axie wants to blow its FETs it will do so, likely without even exceeding current anywhere else.

1 hour ago, PurePower said:

the fuse per string should be lower than the rating of the main battery fuse.... So if the calculation earlier works out to 125A per fuse, does this mean i need to get a higher rated fuse for the Mersen battery disconnect?

I disagree with that. With parallel strings, the current doesn't divide equally between the two strings. Each string contributes relative to its own capacity, you may find that sometimes the one string provides more than the other and they might even switch roles during the discharge cycle. In other words, two 125A fuses don't add up to 250A. To avoid nuisance blowing, those two fuses (and the cables) should be rated at slightly more than half the total current. The main fuse should be sized for whatever is downstream. It's perfectly acceptable for the main fuse to be lower than the sum of the two smaller ones.

Also, with two strings a short in the one string can cause current from the one string to sink into the other one, and the string fuses also protect against that. You could size all three fuses at 125A and that would be perfectly justifiable.

1 hour ago, PurePower said:

where should the BMV shunt be placed on the diagram above?

It goes between the negative busbar and the fuse, in other words, it goes BEFORE the fuse. Let me explain why you do this and why it is not dangerous.

  1. The thin red positive wire that runs between the shunt and the battery positive has its own fuse to protect it. This line is used only to power the BMV and do voltage measurements.
  2. There is a fuse after the shunt that protects that path.
  3. If you put a fuse between the shunt and the battery, the voltage drop across the shunt will affect the BMV measurements.

I hope that helps.

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10 hours ago, PurePower said:

We don't get a 104A fuse, so we settle for a higher one that is available, 125A.

I settled for a 100A fuse. There is a bit of spare capacity in the x25% calculation. In my mind 125A is too high  50% over your max of 83A. I have 100A here in the Karoo and they have not blown in 2½ years constant use. I do like your Mersen battery disconnect.

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