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 > Your search for posts made by 'LScamper' found 53 matches.

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RE: Pure Sine Wave Inverter

I used a 1000W MSW inverter for years on several TVs, DVR, computer, and on my VIP211k sat receiver. It worked fine! Just bought a Samsung 32" TV. When I plugged it into my MSW there was a pretty loud buzz coming from inside the TV. It worked OK but I thought that the buzz was a sign of problems down the road. Better safe than sorry so I bought a 300W Go Power PSW inverter and it works fine, no more buzz! The buzz may be from an inductor in the switching power supply saturating because of the low peak voltage of the MSW inverter. Just guessing on that.
LScamper 01/16/14 06:40pm Technology Corner
RE: HELP AC Outlets blowing devices!

An open neutral between service panel bus bar and utility transformer would smoke things in the house as well as the RV. Problem should be between service panel bus bar and RV distribution panel. Start by loading as mex said but start at the house connector before plugging in the RV. Then work to the RV.
LScamper 01/06/14 09:56am Tech Issues
RE: HELP AC Outlets blowing devices!

MEXICOWANDERER has the best 100% sure way to find an open or high resistance nuetral. Do not plug in anything to the 50A plug until the problem is found. You will just destroy more equipment.
LScamper 01/05/14 09:46am Tech Issues
RE: Multi-meter recommendations, please!

Sorry for the overload! "I know a few people who have private museums of vintage test equipment" You must be talking about me. EICO Model 950B AC bridge, EICO Model 324 RF signal generator, EICO Model 425 5" Push Pull Oscilloscope, EICO Model 232 VTVM, battery eliminator with volt, current and a variac to set it and several other EICO items. Most bought by saving lunch money in 7th > 12th grade, late 50s early 60s. Still have the instruction manuals and the construction manual for them! Also have RCA Senior VoltOhmyst, Simpson Model 377, Triplett Model 666-R, and Triplett Model 310. A few other old meters laying around too. Have several Fluke meters some that I have used from the early 70s. Oh and one TEK RM 45 to heat the house! OK, back to this thread. If he is a true engineer he will appreciate quality equipment. You can'nt get better than Fluke! If he would like an oscilloscope, for about $400.00 on Amazon you can get a Rigol DS1102E 100MHz Digital Oscilloscope. It is a very good scope for little money for a scope. I have had one for about 3 years and really like it.
LScamper 12/21/13 07:05pm Technology Corner
RE: Mixing Batteries on Float-- Mex Test Update 2

A few observations about parallel batteries on float charge or just left connected in parallel. First assume that both batteries are in good shape and full charged. Mex said less than .1V after four or five days no problem. Seems like you could measure how one battery charges or discharges the other. Measure the current in the parallel connection between the two batteries. If they are at the same voltage there will be no current flowing from one to the other and the two batteries will not know they are connected together. If one is lower than the other you could measure the current and from that calculate the Amp hour discharge of the better battery. While in float charge if one battery has an open cell it will not draw any current from the charger and only the good battery will charge. If one battery has a shorted cell it will draw all or most of the current from the charger and may draw current from the good battery discharging it. I can’t think of any other interaction off the top of my head. Do you float charge or leave connected two six-volt batteries in series? If you do it seems that there is all most the same problem as two twelve-volt batteries in parallel. If left connected but not on a charger there is no problem. If one cell is open when float charging there will be no current and neither battery will charge. If one battery has a shorted cell all the good cells will over charge. Should you worry about either case? How often will a good battery go bad when it is left on a float charge or just left alone?
LScamper 12/20/13 10:41pm Tech Issues
RE: Induced power from nearby lines??

pianotuna thanks for the link. I found it fascinating.
LScamper 12/07/13 11:58am Tech Issues
RE: Converter In-Rush Thermistors etc, UPDATE -3

Salvo - like they say a picture is worth 1000 words! It would be nice, if you have time, to see the time delay from turn on to when the converter starts to supply load current. Is the thermistor at the lowest resistance at that time? Also would be interesting to see how fast the load current ramps up. Also would be interesting to see input current when applying load after the converter is powered up and the thermistor has had a chance to cool down. (A small load so it won’t destroy your converter!)
LScamper 12/06/13 01:21pm Tech Issues
RE: Induced power from nearby lines??

A little fun! Why are not these strays being used for good things or products? Maybe, for an emergency situation, you could buy a gadget you could charge your cell phone by unrolling a little wire under power lines. You could park your RV under power lines in the winter to heat it for free. If you live a cold area you could build your house using metal beams and let it heat it self. Maybe you could charge your RV battery by parking under power lines. The possibilities are almost limitless! OK how to measure it for those who know. Using a very high impedance voltmeter, RMS is best, measure the voltage from RV to ground. Then measure the current from the RV to ground with an ammeter. This will give you the Thevenin equivalent circuit. From this you can determine the maximum power transfer, the maximum power that you can use from this source. Will it be megawatts or microwatts? The curious want to know.
LScamper 12/05/13 11:41am Tech Issues
RE: Induced power from nearby lines??

Harvard is perfectly correct. This is a capacitive voltage divider. The capacitor between the power lines and the RV is small compared to the capacitor between the RV and ground. Thus a large voltage between the lines and the RV and a small voltage between the RV and ground. This would hold true even if the lines were DC instead of AC. The current drawn when you ground the RV would be small because the capacitance is small and the reactance is high. This was discussed a few times and I made the same case for a capacitive divider. But no one agreed with me, I don’t expect them to this time!
LScamper 12/04/13 09:15pm Tech Issues
RE: VARIAC....MEX?

Is the carbon sliding contact much different than the commutator brushes in a motor? They seem to last when the motor is turning fast under load.
LScamper 12/02/13 05:56pm Tech Issues
RE: Converter In-Rush Thermistors etc, UPDATE -3

ken white wrote: "The volt-second relationship is only valid for continuous current flow during steady state. If you exceed the kVA rating, with a large impulse current, then my guess is the core will saturate - it is being operated outside of design specifications... " First, I left out that core saturation is due to not enough magnetizing inductance that keeps the unloaded current down. It has nothing to do with load current. If you exceed the kVA rating with a large impulse current you may melt the windings but you will not saturate the core if you have enough V-S! I spent 35+ years in pulse-power. I have designed hundreds of high voltage pulse transformers. V-S is the king, VS=NBA. Current is not involved with core saturation.
LScamper 12/02/13 12:02pm Tech Issues
RE: Converter In-Rush Thermistors etc, UPDATE -3

ken white wrote: "Look at the B-H curves for the various magnetic materials and you will see the B field is controlled by the amp-turns which changes the permeability of the core and induced voltage. We are talking transient conditions and not steady state... Why do you think current has no effect?" B field is controlled by amp-turns --- This is true for DC. For transient and AC conditions the inductance, if designed correctly, keeps the current down and the core from saturating. It is the volt-seconds, that is the number of turns, the saturation flux of the magnetic material, and the size of the core, that determine if the core will saturate. V-S = NBA. Current is not involved.
LScamper 12/02/13 11:30am Tech Issues
RE: Converter In-Rush Thermistors etc, UPDATE -3

ken white wrote: "Not concerned about saturating the core of the transformer, or its kVA rating, when allowing 375 amps to flow? If saturated, the surge current will flow longer than 1/4 cycle and will persist for more cycles too... " ? How does high current saturate the core, volt - seconds stay the same?
LScamper 12/02/13 10:34am Tech Issues
RE: Converter In-Rush Thermistors etc, UPDATE -3

ktmrfs, sorry for not using your complete response. I agree with you but was trying to add something else to think about.
LScamper 11/30/13 11:40am Tech Issues
RE: Converter In-Rush Thermistors etc, UPDATE -3

ktmrfs wrote: "And consider this. As long as the thermistor can handle the inrush current (joules spec) and the power at max steady state current, a higher than "optimal" thermistor initial resistance within reason, really will not hurt anything and has upsides. inrush current will be lower (good), time for the caps to fully charge will be longer, but only by a few cycles, not noticeable. No real downsides." I don't have the answer but one thing seems to be overlooked here. All the talk here is about the capacitor inrush current and steady state current. This is an important part of the design but not the only thing. The thermistor must be hot, in the low resistance state, when the inverter starts to provide the high current output to the battery. If it is not hot enough there will be large power dissipated in the thermistor. This was the case with connecting the battery after the converter was turned on. So it may be argued that using a smaller thermistor close to the ratings is best, but don't turn it on and then connect the battery! As you can see there is no simple answer as all design is a trade off. Getting it correct is often a matter of trial, measure, and rethink it. With this inverter a range of thermistor values should work as long as it is used in a manner that it was designed to, that is do not turn it on and then connect the battery.
LScamper 11/30/13 10:45am Tech Issues
RE: Converter In-Rush Thermistors etc, UPDATE -3

ken white wrote: "Oh, and you can't really ignore the joule specification since a hot restart will have a lower R and therefore the energy dissipated will be much higher." ? So as R goes to 0 the energy dissipated goes to infinity?
LScamper 11/29/13 03:59pm Tech Issues
RE: VARIAC....MEX?

Golden_HVAC wrote: "Many variacs say to not turn the dial with a load on it. I would not be turning the load down to 0 volts before shutting it off. Rather I would shut off the charger first, then with no load you can adjust the voltage." I have used hundreds of variacs over the last 40 years or so. Used to control many kW of power. Most of the equipment needed to start at zero volts and slowly brought up to operating voltage. Shutting down was also a slow reduction of voltage. Some equipment had motor driven variacs that automatically adjusted the voltage, always under load. I don't ever remember a variac spec that said not to adjust under load. It would be interesting to see such a spec.
LScamper 11/29/13 09:55am Tech Issues
RE: Converter In-Rush Thermistors etc, UPDATE -3

BFL13 wrote: "Then from this info above, it seems that clamping on first before start up would make the thermistor need to charge the capacitors plus the load? Is that not worse? I am confused about that." Two things that may be happening when clamping on first. 1. The converter starts to charge the battery slowly as the input voltage comes up. This gives the thermistor time to heat up and the resistance lower before the charge current comes up to full. This lowers the requirements of the thermistor. 2. There is a small time delay from when power is applied and the battery starts charging. This is the same as above. This gives the thermistor time to heat up and the resistance lower before the charge current comes up to full. The problem seems to be a cold thermistor not a hot one!
LScamper 11/23/13 12:28pm Tech Issues
RE: Converter In-Rush Thermistors etc, UPDATE -3

More on The thermistor. Maybe it would be best to start the convertor with the battery connected. I don't know but if the converter connects the battery as soon as the input voltage is up the thermistors are already hot and in a low resistance state. This would reduce the energy requirements of the thermistor and be in their operating range.
LScamper 11/23/13 11:40am Tech Issues
RE: Converter In-Rush Thermistors etc, UPDATE -3

The problem now seems to be well defined. The thermistor is blowing when the battery is connected after the converter has been on for a while and not connected to the battery. Is this correct? This tells me a few things. The converter inrush current at turn on is not the problem. The thermistor will handle the initial inrush current. So what is happening? The converter is turned on and the initial inrush current charges the input capacitors. The thermistor has heated up somewhat during this time and the resistance is going down. The thermistor is rated to charge this input capacitor. Now the converter is sitting there with no load on it. This means there is very little current through the thermistor and it is now cooling off. The resistance is going up toward the cold value. Then the battery is connected. This is the same as turning on the converter with no load on it. There is a large inrush current that the thermistor moderates. The problem now is that instead of charging the input capacitors you are trying to charge the battery. This is the same as having a huge input capacitor that the thermistor is tying to charge. It is not rated for that and is being blown. This is a design defect! What to do? There may be nothing you can do without a redesign. You need a much bigger thermistor, don’t know if they make such a thing. One thing I would try is connecting several 5 ohm thermistors in parallel. I know you should not parallel thermistors. They may share current at startup enough to provide the energy absorption need at battery connection. I’m not going to try to calculate the best configuration of thermistors but maybe someone else will. Hope this helps.
LScamper 11/23/13 11:24am Tech Issues
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