Amps or watts?

[William Marshall Moore]

Dodge manufactured my 1990 van with what they rate a 120 amp alternator, made in Japan, for which they nor retailers provide brushes, diodes, or bearings and requires metric wrenches.<p>They harnessed it exactly as the 60 & 90 amp alternators, that is by #6 copper on both supply and return with the output protected by a green # 10 fuselink ~ 6" long. No one has been able to provide fuse link specifications. The manufacturer is non communicative. I do not believe that I will ever buy a motor vehicle that is not fully depreciated.<p>I have installed a dual battery system, A+B, AorB. I reused a Guest 60 amp isolator with the Smart Switch and solder lugged ~ 100' of 00 copper welding cable that was lying around the shop and is now lying around in the van. For some time I have been pleased with the result. I am able to DC weld at 12 volts anywhere in the van. I am still trying to choose between
Datastorm.c (mobile satelite, bookmobiles etc.
or one of the cellular providers. Unless they give something for my 2 year committment, that is Quid Pro Quo, I believe that the contract is unenforcable. On the other hand I intend to discover why they are not required to operate under public utility rules. Do I smell another class action suit?<p>Cogitating about the alternator wireing issue I ordered a $75.00, 130 amp max American made isolator from units-direct.c and designed and built a 120 amp fuse holder, paralelling two 60 amp/ 250 volt fuses.<p>On my constitutional with the dogs this morning it suddenly occured to me that watts blow fuses and not amps. I am still unconvinced and do not wish to use one time only fuses to experiment.<p>Who can definitively and more succinctly than me put this querie to bed. <p>Next time I shall probably talk about the Bulldogsecurity.c remote starter installed to be operated by thermostat to climate control the dogs. Bulldog technical support and now customer service refuse to answer my mail. My strategy in such cases is to file with the FTC, the primary and any secondary BB, and to report all mail fraud to the Postmaster General. This last step always guarantees a formal investigation by the U.S. Poastal Service. Many times other crimes more serious can then be discovered and delt with.<p>Sincerely,<p>William Marshall Moore

[cato]

Watts blow fuses in the sense that fuses have some resistance associated with them and it is the I(current)-squared-R(resistance) (i.e.;Watts) heating that melts the link and causes the fuse to "blow".<p>In paralleling your fuses, you appear to be assuming that they will share the current equally. This is probably not the case. One will carry more of the load than the other (because of a difference in resistance, either in the fuses themselves or in the respective legs) and "blow" before the total current reaches the 120 amp rating I think you are hoping for. My guess is you will get something close (100 amps?), but then one fuse will blow, the whole load will be carried (briefly) by the other fuse and then it will blow.<p>Does that help?

[Bernius1]

Pollack and some others make ckt breakers up to 100Amps. Mack trucks for years have had one on the right side above the battery box (40Amp). Call your local dealer.

[William Marshall Moore]

Per usual, I incorrectly framed and phrased my question. <p>Since power is required to cause lead links to fuse, and they are rated at amps at voltage, what is the effect of dividing the voltage by 10 as in the case of using 120 volt fuses at 12 volts or dividing by 20 when using 240 volt rated fuses?<p>To avoid paralell circuit resistance differences, I have bound the two fuseholders together mechanically by bolt and hose clamp and electrically by solder. And difference between the two circuits at the fuses will be determined by fuse shell connection. Here also I have tinned all contact ares save the fuses themselves, and I am sure that I could tin the fuses by working on a small area at 50 watts. Additionally the pathes are also interconnected at both the supply side, the alternator output stud, and the load, the input stud of the isolator. I suppose I could dust off the Keithley Micro-Ohmmeter and measure the differences. I wonder if I left the ni-cds inside. In 15 years the one #6 copper, #10 green fuselink, have satisfactory so I should be aware of additional loads and be prepared to deal with casualties. Four 300 watt quarts luminaries would be a good test and at 120 volts inverter conversion efficiency will need to be taken into consideration.<p>I have no interest in the P4400 Kill A Watt and I ran across their add in Nuts and Volts. I ordered one and it cost $40.00 including shipping. It is rated at 125VAC/50/60/15A/1875VA. It displays seven modes, V/A/W/VA/HZ/PF/KWH/HR. It totalizes KWH & HR. Guaranteed .2% accuracy. In my opinion a good bargin. If some one knows of a better, I would like to be told about it. Quantaties can be had at discount.
My contact is Tim Johnson at 808-778-6674.<p>Sincerely,<p>William Marshall Moore

[Chris Smith]

You can not use 120 or 240 volt fuse rating at 12 volts. There are many factors that a fuse is designed to consider, and 12 volts is not one of the considerations.

[dyarker]

You can say that fuses blow on Watts instead of Amps, but the volts in V*A is a result of the drop across the fuse due to the fuse's resistance. Not the voltage rating of the fuse!<p>The voltage rating of a fuse is how much voltage the fuse can interupt. A 12V fuse in a 110V circuit could continue to conduct through the melted/vaporized metal after its blown.<p>So a higher volt fuse can be used in a lower volt circuit circuit. But, for the same current rating a, a 12V fuse will have thicker link with a lower melting temperature than a 120V fuse. There are at least two reasons for this. At 120V, one or two volts lost across the fuse won't be missed. A 12V fuse needs a lower resistance for less loss. Also, 12V fuse links need to be thicker for physical strength (ie potholes).<p>In practice, two same part number fuses would handle about 90% - 110% of two times the current rating due to manufacturing tolerances. (No two fuses are exactly the same.) (Put two 50 amp fuses in parallel for a 100 amp load, one may blow at 45 amps. The other will immediately follow because it then has 95 amps throygh it.)<p>Doing this is a kludge. You can "get away with it" at 12V, a definate no-no for 120/220VAC.<p>Cheers,

[Crowbar]

The voltage rating is there to indicate the resulting arc that the fuse can safely interrupt. The higher the voltage the longer the fuse. Amps are amps no matter the voltage and its AMPS that blow fuses, else they would be rated in watts. More information on fuses can be found at www.bussmann.com/<p>[ February 20, 2004: Message edited by: Crowbar ]</p>

[William Marshall Moore]

Thankyou, Gentlemen.<p>WMM

[Tparker]

Waytekwire has automotive/truck/bus fuses up to 250 amps and circuit breakers up to 150 amps.

[upsmaster]

crowbar you got it right.....but u can measure across the fuse while current is flowing through it this voltage drop times known current through fuse will tell you the loss in watts of the connections in this parallel arrangement and how balanced the current flow is and this number will probably vary as the current increases so try to pick a high test current to make sure they share to a point that will work for you
joe

[rshayes]

Paralleling fuses is usually not recommended. They are not manufactured to very tight tolerances. Two fuses from the same lot of materials, if made by the same machine within a short time period, might be matched to each other. Fuses made by different manufacturers or at different times by the same manufacturer probably will not be matched.<p>The melting point of the fuse element has to be fairly high so that the fusing current will be reasonably independent of the ambient temperature. If the environment of one fuse is different from the other, such as being mounted closer to a metal wall, the fuse may behave differently, due to differences in cooling by either radiation or convection.<p>Small instrument fuses (usually 10 milliamp) used to be used to detect microwave power. When operated at close to rated current, these had a high temperature coefficient. If removed from the cartridge, they were sensitive to small air currents, such as someone walking by several feet away. At slightly more than rated current, they would glow red before blowing. Larger fuses are probably not this sensitive, but I would still expect some environmental effects.<p>[ February 22, 2004: Message edited by: stephen ]</p>

[rshayes]

Years ago, I was driving a 1964 Dodge Van when an alternator diode shorted out. There was no fusible link, and the current from the battery melted the insulation in the wiring harness, resulting in practically every wire being shorted together before I got the battery disconnected.<p>After replacing the wiring harness, I installed a circuit breaker purchased from a surplus store. I think it was rated at 50 or 60 amps, but higher currents are probably available. Airpax (www.airpax.net) makes this type of circuit breaker, and there are probably other sources. <p>The circuit breakers used to protect house wiring may also be usable. These are designed to interrupt 110 VAC, so they should be able to interrupt a 12 volt DC circuit.

[William Marshall Moore]

I just ordered an item # 46927, HI AMP MANUAL RESET 120 AMP SURFACE MOUNT breaker for $20.33 shipping? from WAYTEKWIRE.c.
They responded immediately to my friday evening querie about fuses in the negative and offered to find them for me. I thanked them and told them that it was my job.
WMM

[William Marshall Moore]

Bats, that is 120 amp fuses.