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Old 09-12-2013, 10:28 AM
evmetro evmetro is offline
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Default Main Pack Fuse Selection

My EV education has come a long way since the beginning, but there are still some things that are a little vague, and how to properly select the right main pack fuse is one of them. In my first conversion, I have a shawmut fuse that says 500 amp 300 volts AC on a 108 volt pack that powers a 650 amp curtis 1238. I selected this by calling an EV supplier and telling them about my EV and then I bought the one they recommended. I now have need for three more various pack fuses for various builds that I am doing right now, and would like to know how to come up with the correct ones based on a my own knowledge. Can somebody point me the right way? If it helps any, the builds that I need fuses for are a 153.5 volt 400ah pack running two 1238 144 volt controllers, a 115 volt 200ah pack running a single 1238 650 amp, and a 144 volt 100ah pack running a raptor 1200 controller.
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Old 09-14-2013, 05:12 AM
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Default Re: Main Pack Fuse Selection

The primary function of a fuse is to prevent a fire in the event of an overcurrent condition such as a short circuit. Usually the wiring is the weakest link and would burn first, but in some cases it is the 'box' that requires protection. It must be large enough to handle the normal operating and inrush and transient currents to avoid nuisance blows, yet fuse without fire when an overcurrent occurs. There are also time-delay features to consider. Here is a good link about selecting fuses: http://www.schurterinc.com/content/d..._Selection.pdf
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Old 09-14-2013, 10:03 AM
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Default Re: Main Pack Fuse Selection

You need a suitable DC voltage rating and the ability to break the maximum current you pack will dump into a short circuit. The Zilla manual suggests using Ferraz Shawmut A30QS. These have a 300 volt DC rating at are rated to interrupt 100,000 amps (!).

For the 153.5 volt pack that is feeding 1300 amps peak controller current, and for the 144 volt pack with a Raptor 1200, I'd pick an A30QS700. That is a 700 amp fuse that will take about 3 minutes to blow at 1300 amps. My Zilla manual recommend an A30QS500 for the 1000 amp model and an A30QS800 for the 2000 amp model.

For the 115 volt pack feeding a 650 amp controller I'd suggest A15QS500 because you don't need the higher voltage rating of the A30 series. I may move down to a A15QS250 with my Zilla because my pack is under 150 volts and I have the controller current set to 300 amps, with a long hang time at 300 amps because the motor current is set to 900 amps. I'm currently using the standard A30QS500.
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Old 09-14-2013, 11:31 AM
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Default Re: Main Pack Fuse Selection

Thanks for the replies kenney and evfun. I checked out that pdf and some others on the web, and it seems challenging to find much on big DC fuse selection. One thing that I did notice, was that the DC volt rating tends to be about half of the AC volt ratings for the same fuse. My head is swimming with all the fuse approvals, IEC ratings, UL characteristics, trip characteristics and such. I wish that there was a translation of all this stuff that was broken down into a simple guide for the DIY electric car guy to make a good choice and know why it is a good choice. I will keep studying and maybe I can write a fuse guide one day that is targeted at the DIYer EV folks who have day jobs that have nothing to do with converting EVs.
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Old 09-14-2013, 11:42 AM
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Default Re: Main Pack Fuse Selection

Here is a quick link to the manufacturers information about the A30QS line of fuses. They list the ratings and have charts to blow times at different overloads.
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Old 09-14-2013, 12:49 PM
evmetro evmetro is offline
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Default Re: Main Pack Fuse Selection

What is the reason for melting time? If your controller is rated for 500 amps max, why would you not just have the fuse blow the moment the circuit exceeds 500 amps? I assume that there is a reason that the shawmut fuses are popular in EVs, is there something that these semiconductor fuses are so often selected over others? I have read that an ANL fuse could still conduct electricity after they blow due to arcing across the blow... What should I look for in a fuse that will ensure that it blows correctly?
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Old 09-14-2013, 01:58 PM
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Default Re: Main Pack Fuse Selection

Quote:
Originally Posted by evmetro View Post
What is the reason for melting time? If your controller is rated for 500 amps max, why would you not just have the fuse blow the moment the circuit exceeds 500 amps? I assume that there is a reason that the shawmut fuses are popular in EVs, is there something that these semiconductor fuses are so often selected over others? I have read that an ANL fuse could still conduct electricity after they blow due to arcing across the blow... What should I look for in a fuse that will ensure that it blows correctly?
Everything takes time Define moment. A second? Millisecond? Nanosecond? And it is not a fuse made from semiconductor; it is a semiconductor protection fuse. The fuse contains an element which will melt in a very predictable manner. Its characteristic is often described by using It. The fuse manufacturer will have more accurate charts showing when the fuse will blow depending on the current. You select the fuse to best suit your application.

If you actually need a device to protect by opening the circuit exactly at a set current (500A) instantly (milliseconds), then you would need to use a contactor or switch (transistor) with a current sensing circuit instead of a fuse or circuit breaker which rely on a thermal element. And good fuses (like Shawmut) are expensive but worth it IMO. Company reputation and product quality go a long way in the decision process I use for personnel and property protection.
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Old 09-14-2013, 02:52 PM
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Default Re: Main Pack Fuse Selection

Major, I can't define "moment" at this moment, and is one of the things that I would like to understand. What is the most appropriate "moment" for a high voltage pack? Are there reasons in an EV packs that dictate how long we would want for a fuse to blow? I have seen the manufacturer charts of specs for various fuses, but to select a fuse and understand the charts I need to already know what length of time I need for it to blow as well as a number of other things. I have seen many threads here where it has been advised to not use ANL fuses, and I have even seen an occasional fuse suggestion, but not anything about how to determine how slow or fast you want your fuse to blow.
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Old 09-14-2013, 03:45 PM
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Default Re: Main Pack Fuse Selection

Quote:
Originally Posted by evmetro View Post
What is the reason for melting time? If your controller is rated for 500 amps max, why would you not just have the fuse blow the moment the circuit exceeds 500 amps? I assume that there is a reason that the shawmut fuses are popular in EVs, is there something that these semiconductor fuses are so often selected over others? I have read that an ANL fuse could still conduct electricity after they blow due to arcing across the blow... What should I look for in a fuse that will ensure that it blows correctly?
Just my .02 ,
the fuse is not there to protect your controller, the fuse is there to protect your wiring from overheating and caching on fire in case of an overload. If your controller is not smart enough to protect itself than it will almost always burn before your fuse. So , the fuse will be calibrated in direct relation with the wire size, and the wire size will be calibrated in relation with the controller and battery pack specifications .
Because of that, no controller manufacturer will list a fuse value in the controller manual.
And again the fuse is not there to protect the controller, more likely is there to protect your wires when the controller blows and make a short circuit.
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Old 09-14-2013, 04:18 PM
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Default Re: Main Pack Fuse Selection

Thanks. I listed controller size as an example since it is the biggest load that the pack sees, and I figured that if the pack sees more load than that, the fuse should blow. If I understand correctly, the smaller the fuse rating, the more protection, but too much protection could mean blowing the fuse during normal use? This would mean that if a controller draws 500 amps max, the fuse should be higher tham 500 amps? Say you have a 500 amp controller, and say a 100 volt 100ah pack, and say 20 feet of 0/1 cable. What would you do with these numbers to select an appropriate fuse? Are there other things besides these basic parameters that should be considered? How fast or slow would you want it to blow, and why that speed?
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