Check out KB:
http://digital.ni.com/public.nsf/websearch/E8064C591C5FDA1A86256A4D00817C1C?OpenDocument
Also:
Title:
Troubleshooting Blown Fuses in an SCXI Chassis
Problem:
The main fuses in my SCXI-1001 chassis are continually blowing. Is there something wrong with my SCXI chassis or with my overall system�s power? Would it be possible to see the power schematic for the chassis so I can analyze the power requirements?
Solution :
It is not uncommon to blow the main slo-blow power fuses in an SCXI-1001 if they are used under the wrong conditions or if there is damage to one of your SCXI modules. Each module presents the power supply with a load. The more you load down the power supply the more current it draws, and the more likely you are to blow a fuse. We test the SCXI�s power supply with the equivalent of the worst load possible before shipping, so there is no combination of modules that will draw to much current to blow the fuse.
The schematic for the power supply is closely coupled with the rest of the SCXI chassis and is considered proprietary information. Most customers who ask for this are trying to troubleshoot a problem with the power in their system. The customer should first verify the installation of his hardware. If this is fine, then you can recommend some of the suggestions below.
Here are a few suggestions that the customer should keep in mind:
1. A common problem is that once a blown fuse occurs in a chassis, that fuse is replaced with a non-slow blow fuse. This will cause the fuse to blow again very quickly and can result in you going through a number of fuses. The reason for this is that when you turn the chassis power on, the ramp current is higher than 1.6A; however, the current stabilizes after a few seconds to about 1.4A. The current should not go above that level for an elongated amount of time unless something is wrong, and then, by design, the fuse will blow so that components are not damaged. Refer to the links below to see a list of the recommended fuses for an SCXI chassis.
2. Check to see what modules are in the system and if removing one of the modules stops the fuse from blowing. If this is the case, then most likely one of the modules is damaged and contains a short, thus causing too much power to be pulled from the chassis.
3. The fuses will often blow if you are using 100VAC (the Japanese standard)
4. Verify that you are getting the correct amplitude of the power. If there is a chance that the power is dirty or in the incorrect amplitude range, then we recommend using an UPS (uninterrupted power supply) with line conditioning. The �line conditioning� is important as it will filter the output to the chassis.
5. Check to see if devices nearby might be causing large spikes, noise, or other transients to be introduced into the power grid. These devices might include inductively switched loads such as motors and solenoids that are also connected to the power grid nearby. Also, check for other large Electro-Magnetic Interference (EMI) producing devices nearby such as arc welders and generators. You may actually be able to associate the timing of any of these things nearby with the behavior. If you cannot switch to a UPS, then a quick solution might be to place a ferrite ring (choke) around the power cable near the chassis for EMI suppression or insert an isolation transformer between the supply and the chassis. NI has one ferrite ring that could be sent to them (p/n 711856-01) if this seems like a possible solution.
6. If you are sure that there is no problem with the power, and no problem with the chassis or any of the modules, then you can try using a larger fuse, though this is NOT officially recommended by NI, and VOIDS THE WARRANTY. The following website has listings of possible fuses to try, such as:
- 1.6A Time Lag Slo-blo (NI Part Number: 766105-01, Littlefuse Part Number: 23901.6)
- 2.0A Time Lag Slo-blo (NI Part Number: 766181-01, Littlefuse Part Number: 218.002)
- 2.5A Slo-blo (Littlefuse Part Number: 239.025)
