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 > Your search for posts made by 'LScamper' found 39 matches.

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RE: Unknown Brand AC/DC Inductive Ammeter?

This is a review of the meter. Clicky
LScamper 11/09/14 10:05am Tech Issues
RE: Cannot connect to public WiFi

Had the same problem with a new Dell Windows 8.1 desktop out of the box. Would connect but no internet access. Called Dell, after many things to try no luck. It was new and nothing had been installed. They said try to do refresh to new condition using windows recovery. After doing that it worked perfectly and I never had a problem with it again. All so have an HP laptop. I could not get some programs to run sometimes on it. Tried for several weeks. Gave up and did a refresh to new condition. Never had a problem with it after that. Strange that two new Windows 8.1 computers had bad Windows installed from factory. Just luck I guess, but strange. Both have been working perfectly for months now.
LScamper 11/07/14 10:22am Technology Corner
RE: Paralleling Power Supply Units Made Easy ???

Yet another stability paper. About the same as the one Salvo noted. It shows how to measure stability in a CLOSED LOOP system. You do not have to open the loop. It injects a stimulus into the loop. Is this the same as injecting a stimulus as in connecting another power supply in parallel? I think so. As long as the stimulus is not so big that it causes the loop to saturate it seems it should work. http://www.edn.com/design/power-management/4412230/Testing-a-power-supply---Stability--Part-three-
LScamper 11/04/14 12:12am Tech Issues
RE: Paralleling Power Supply Units Made Easy ???

From this EDN note "Multiple PSUs share load" Using diodes to isolate power supplies. http://www.edn.com/design/power-management/4419835/Multiple-PSUs-share-load The results were disappointing, since they show that in the case of ±1% voltage deviation, 90% of the power is supplied by a single supply. Basically, this circuit is not a good solution for power supplies with more than a few tens of millivolts difference. The problem is that not all off-the-shelf power supplies have output voltage adjustments – especially not the sealed ones. To solve this issue, a circuit was developed to ensure load sharing using off-the-shelf power supplies and components (Figure 2).
LScamper 10/27/14 10:26am Tech Issues
RE: Paralleling Power Supply Units Made Easy ???

Salvo wrote: “That's not quite right. The supply that sees higher voltage than it's setpoint will just shut off. The pwm duty cycle will go to zero percent. This is a very safe condition for the supply.” Correct, this is one of the condition that I think could happen. “When the first supply reaches its setpoint it goes into constant voltage mode. When the other supply charges the battery voltage above that set point the first supply's control loop tries to lower the voltage to its setpoint, it can not do that. It will keep trying and will saturate. At that point the first supply is operating open loop. Depending on the supply design it may just shut the output off, a good thing.” Condition 2: “It is possible that the error amp, being over driven, will saturate and reverse its output if it is not designed well. This would turn on the output to full voltage, a bad thing!” Salvo wrote: “ You're not going to overstress the error amp either. The amp is probably powered by 12V. The reference voltage to the error amp is usually around 5V. If the first supply is at 15V then the second supply needs to go up to 15V * 12/5 = 36V. That's highly unlikely that the two setpoints are that far apart.” It has been many years and my memory is not what it use to be! My terminology may be wrong when I said error amp is over driven. What I am trying to say is that at the point that the control loop, while trying to lower the output voltage, will at some point saturate. At this point I agree with what you say. “The pwm duty cycle will go to zero percent.” At this point the control loop is now open loop. When it is open loop there is no feedback to drive the + and – inputs to the error amp to the same voltage. A long time ago operational amplifiers had a nasty habit of reversing or latching their outputs in the opposite direction than it should when this happened. This would turn the converter output full on, a bad thing. Maybe this condition can no longer happen, I don't know. With parts being made in China I would not bet on anything. From MEXICOWANDERER's last post it seems as if something bad happens when paralleled! Maybe what I just said?
LScamper 10/19/14 05:29pm Tech Issues
RE: Paralleling Power Supply Units Made Easy ???

Some thoughts: Salvo wrote: “Having designed many dc/dc converters, I see this stability issue way over blown. If the ps has a phase margin of 45 degrees, then guaranteed, there's no stability issues. 30 to 45 degrees of phase margin is standard design practice.” X2. I see no problems with paralleling two supplies under some conditions. While they are both in constant current there should be no problem. If there is diode isolation between them there should be no problem. I do see a problem if there is no diode isolation and one supply reaches its voltage set point and the other is still charging the battery. When the first supply reaches its set point it goes into constant voltage mode. When the other supply charges the voltage above that set point the first supply's control loop tries to lower the voltage to its set point, it can not do that. It will keep trying and will saturate. At that point the first supply is operating open loop. Depending on the supply design it may just shut the output off, a good thing. It is possible that the error amp, being over driven, will saturate and reverse its output if it is not designed well. This would turn on the output to full voltage, a bad thing! I can only guess that these cheap supplies are not designed worrying to much about all the possible ways they will be used. I don't think anyone can say exactly how they will react to being paralleled without a complete knowledge of how they are designed.
LScamper 10/19/14 01:16pm Tech Issues
RE: Buck Your Solar with a Mex Gizmo?

Just a few thoughts (or lack there of). It will be interesting to see what happens when you drive a buck converter with a constant current source (gizmo between panel and controller). I think that the panel voltage and converter output current will go into wild oscillations at the point that the load (battery) is asking for more power than the panel can provide. “I can use some resistance between the panel and the gizmo to reduce its input voltage to less than 32v.” When the gizmo is not asking for any current there will not be any voltage drop across the resistance and the full open circuit panel voltage will be at the gizmo input! Some have suggested using a power supply to drive a solar controller. This woud be interesting also, driving a controller that is made for a current source input with a voltage source input. If it is a MPPT controller will it try to find the maximum power point. That is will it lower the input resistance trying to find the maximum power until it burns itself out? Just wondering.
LScamper 10/13/14 09:00pm Tech Issues
RE: LCD Backlit DC Voltmeter (doesn't require power)

RoyB wrote: "I DO NOT want to go with the SHUNT TYPE current taps as then I have to deal with high current 'HOT' DC wiring running back to my meter console." Put a 2K resistor on each of the shunt meter leads at the shunt. Then run the meter to the other side of the 2K resistors. The resistors will not change the meter reading and will limit any short circuit current to a harmless value.
LScamper 09/19/14 09:03am Tech Issues
RE: solar fuses

Reprint from 4/10/2014 RE: Proper Fusing Of Three Parallel Panels Trying to make sense of panel fusing. A fuse is a current protection device. A fuse at the output of a panel is to protect the wires from the fuse to whatever it is connected to, mainly the controller. An array is the parallel connection of two or more panels (strings). A string is the series connection of two or more cells. A panel can be say 30 cells or 90 cells. A string can be one panel of say 90 cells or three panels of 30 cells in series, same exact thing! Say a panel is rated at 10A short circuit current and the fuses are 15A. So what happens if there is a short directly at a panel before the fuse? If there is only one panel the panel output goes to zero and the controller gets no input. The fuse will not blow, no current through it. If there are two panels in parallel and one shorts directly at a panel the output the voltage goes to zero and the controller gets no input. The short circuit current supplied by the other panel, 10A, now goes through both fuses, the one on the good panel and the one on the shorted panel. Neither fuse blows because they are rated to handle the current from one panel. The wires are safe because they are rated to handle at least the short circuit current from one panel. If there are three panels in parallel and one shorts directly at a panel the output voltage goes to zero and the controller gets no input. The short circuit current supplied by the other two panels is added, now 20A total, and flows through each of the good panel’s fuses, 10A each, and through the shorted panel fuse. This fuse now gets two times its normal current, 20A, and should blow from over current. When the fuse blows the voltage goes up at the controller and will still charge the battery from the two good panels. If the wire is rated to handle the current from the two good panels no fuse would be required. This would be the case in most of the installations talked about on the forum; most use much larger wire than needed to keep voltage drop at a minimum. This brings us to a reason not to use fuses at the panel, voltage drop! In order for a fuse to blow it has to dissipate some power to heat it to the melting point. This means that the fuse must have resistance. A 7A fuse resistance is about .013 Ohms and a 10A fuse resistance is about .008 Ohms. A 10-gauge wire has a resistance of about .001 Ohm per foot. So adding a 7A fuse is like adding about 13 feet of 10-gauge wire from the panel and a 10A fuse is like adding about 8 feet of 10-gauge wire. Plus there are all the connections that add resistance and could become loose or not a make good connection. Bottom line is if the wires from each panel can handle the total current from all the panels, most likely they can, there is no reason to use fuses and they introduce voltage drop plus added connections.
LScamper 09/18/14 09:01am Tech Issues
RE: eTopxizu (cheapowatt) 30 amp power supply Guinea Pig

Edit my last post, not enough coffee! "As you increase the output the inductor stays on longer and the voltage across it increases." Should be: As you increase the output the inductor stays on longer and the CURRENT increases.
LScamper 09/15/14 09:54am Tech Issues
RE: eTopxizu (cheapowatt) 30 amp power supply Guinea Pig

OK first things first. The D13009K that you ordered is not an FET, it is a transistor! I don't know what the actual part that gave up is, I have not tried to look it up. You can not just replace a transistor with an FET!!! The drive circuit is much different. Second, the buzzing most likely is an inductor saturating. As you increase the output the inductor stays on longer and the voltage across it increases. At some point it will saturate. When that happens the current will spike in the output transistors or FET which ever is used. When the current spikes the power dissipation (heat) increases rapidly as you have seen. Next is the rating of the transistors that you ordered, 12A. With two in parallel as it looks to be that would only be good for 24 Amps. Surprised they survived at 30 A, but still not sure what the actual parts in the supply are.
LScamper 09/15/14 09:14am Tech Issues
RE: Dead USB port

Just had the same problem, 2 of my 4 ports stopped working. Called service and ran their tests. They said it had to go in for repairs. I needed to remove the power and remove the battery to get the serial number, had the battery out for at least five min. When I put the battery back in and plugged it in the ports worked! No more problems after about a week.
LScamper 08/19/14 08:29am Technology Corner
RE: Mushroom Cloud Over Mexico LED Magic Smoke Tomorrow

"I gotta try it. (4) 33 volt LED chips in series. (1) 5 amp 1KV rectifier in series for a guarantee (1) 100uf 450 volt electrolytic cap connected inside the rectifier circuit. Plugger into a wall socket. I shall wear a safety shield mask and gloves.... Line voltage in Mexico is rated 127 vac." 4 x 33V = 132V voltage across LEDs 1.414 x 127 = 180V!! "Mushroom Cloud Over Mexico LED Magic Smoke Tomorrow"!!
LScamper 08/13/14 04:50pm Tech Issues
RE: Sizing MOSFET Heat Sink

Long day Salvo? "Max power at 50A is: P_max = 4.5 mohm * 50A = 2.25 W" P_max = 4.5 mOhm * 50A * 50A P-max = 11.25W Have a great day!
LScamper 07/12/14 02:00pm Tech Issues
RE: Sizing MOSFET Heat Sink

Don't need much of a heat sink for this little power. This will give you some idea of what to use. Clicky
LScamper 07/12/14 08:53am Tech Issues
RE: ADJUSTABLE POWER SUPPLY CUTIE

12V 100W led http://www.youtube.com/watch?v=CxnP-6EZ3ZQ Variable DC Power Supply 30v 5a http://www.youtube.com/watch?v=4H6iwiPIaJI High Power LED Forward Voltage Tutorial http://www.youtube.com/watch?v=S5IICsTwTYE 305 DC LAB POWER SUPPLY REVIEW http://www.youtube.com/watch?v=A3yZTSAd8YE
LScamper 05/24/14 11:22am Tech Issues
Battery infromation

This information is for AAs but most of it will scale to 12V lead acid batteries. May be interesting. Clicky
LScamper 05/21/14 07:58pm Tech Issues
AA battery testing

This is a cheap way to test your AA batteries to see if they are charged. Wonder if it would work with lead acid batteries? Clicky
LScamper 05/21/14 05:24pm Tech Issues
RE: QUESTIONS re: MEGA-WATT 33-AMP POWER SUPPLY

Not an answer, just a question. The statement that they will burn out if parallel makes me wonder why. Is it that if one supply is set for a higher output voltage than the other it will supply a high current back into the lower voltage supply? (The lower voltage supply can sink current as well as supply it). If not then it seems that the higher voltage supply would just supply all the current and be limited as if only one supply is not connected. The lower voltage supply would do nothing. If it is because the supply can sink current as well as source it there could be a big problem. How would the supply know if another supply was parallel with it or a battery instead of another supply? If the battery voltage was higher than the supply would it burn out the supply? Just wondering.
LScamper 04/29/14 07:54pm Tech Issues
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