gregc of course you're not going to have these problem with a PowerCab if you add a booster or a circuit breaker. richhotrain gregc The PowerPro documentation says that the PowerPro is rated at 5A and will shutdown if a short is present for more that 1/2 sec. It's unclear what it does if it operates at 6A for many minutes. 6A is not a short.
of course you're not going to have these problem with a PowerCab if you add a booster or a circuit breaker.
richhotrain gregc The PowerPro documentation says that the PowerPro is rated at 5A and will shutdown if a short is present for more that 1/2 sec. It's unclear what it does if it operates at 6A for many minutes.
gregc The PowerPro documentation says that the PowerPro is rated at 5A and will shutdown if a short is present for more that 1/2 sec. It's unclear what it does if it operates at 6A for many minutes.
The PowerPro documentation says that the PowerPro is rated at 5A and will shutdown if a short is present for more that 1/2 sec. It's unclear what it does if it operates at 6A for many minutes.
6A is not a short.
Alton Junction
I ran my Power Cab with some sound locos and shut down the cab a few times but never damaged the Cab. No idea hwo someone did.
I did the quarter test a few times and the Cab tripped. No problem.
The club did test with the Power pro a few times and no problem.
The only issue with the Power pro was when we had fourteen blocks switching from DC to DCC and still ran HO DC and DCC we had somone cross a block with couple DC locos and smoked the booster. The DC throttle could handle three amps.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
There's a big difference between the PH-Pro and the powerCab with regards to the track power circuitry - in the PH-Pro you have a much bigger METAL case that helps dissipate heat. Pretty sure on pictures I've seen of the insides there's a large heat sink attached to the drivers that control the track power. That SHOULD give them components plenty of head room over the nominal output power for the protection circuitry to trip without frying anything first. But in the PowerCab - they had room left over after the normal cab functionality (remember is it and can be used as a normal ProCab when plugged in to a PH-Pro system) that they were able to add the circuitry to generate a DCC sisgnal to the rails. But that was squeezed into a PLASTIC case that already has lots of other components in it. Not much room for a heat sink, either, if there even is one attached to the main power driver. This can be perfectly fine, depnding on the intended use. In the data sheet of power drivers and things like voltage regulators, there are specificatioons for maximum current, assuming a heat sinking capacity that is alsooo specified. Using less or no heat sink, the devices won't instantly fry, but they will be unable to deliver that same maximum power without failing. Combined with an enclosed plastic case with little or no ventilation, you can build up quite a bit of heat, certainly enough to melt plastic. 2 amps at 15 volts is 30 watts - ever try to touch a 25 watt light bulb? Pushing it to 3 amps is 45 watts. Seems reasooonable to me that running the thing continuously at 3 amps is going to cause issues. If not melting the case, then way overheating the internals of the power device. Not knowign what they use, I can;t look at a data sheet, but the data sheet would also have information on the temperature rise of the device internally, and maximum allowable temperature. This can be a temperature that is far higher than comfortable to touch, while the attached heat sink remains just warm.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
(unable to quote)
rich
the doc say short protection. we know it works.
So yes, I was asking what happens if you exceed the 5A rating of a PowerPro by 1A.
if there were a circuit breaker set to 5A, wouldn't you expect it trip?
greg - Philadelphia & Reading / Reading
rrinkerIn the data sheet of power drivers and things like voltage regulators, there are specificatioons for maximum current, assuming a heat sinking capacity that is alsooo specified. Using less or no heat sink, the devices won't instantly fry, but they will be unable to deliver that same maximum power without failing. Combined with an enclosed plastic case with little or no ventilation, you can build up quite a bit of heat, certainly enough to melt plastic. 2 amps at 15 volts is 30 watts - ever try to touch a 25 watt light bulb? Pushing it to 3 amps is 45 watts. Seems reasonable to me that running the thing continuously at 3 amps is going to cause issues.
Combined with an enclosed plastic case with little or no ventilation, you can build up quite a bit of heat, certainly enough to melt plastic.
2 amps at 15 volts is 30 watts - ever try to touch a 25 watt light bulb? Pushing it to 3 amps is 45 watts. Seems reasonable to me that running the thing continuously at 3 amps is going to cause issues.
since DCC is PWM, the power dissipated by the circuit is based on the on resistance of a mosfet and the max current being supplied.
The on-resistance for some high power mosfets i have is 0.04 Ohms. At 10A, each dissipates 4 watts (R * I^2). Since there are two mosfets active at a time in the H-bridge, that's 8W. Isn't 8W comparable to todays LED lamps?
there would be 0.36 W in a PowerCab supplying 3A, if similar mosfets are used. I don't see any openings in the PowerCab for ventilation. (maybe I should cut some).
Assuming they are using power MOSFETs for the H bridge driver. Have to dig in and see just what they are using. There is an integrated audio amp IC that is often seen in low power (~3 amp) DIY booster designs that likely does not have such a favorable RDSon. Somewhere I have a couple, I once was going to build one for an accessory power booster. It requires very little in additional circuitry to take a low power DCC dignal and produce a proper track level output.
gregcthere would be 0.36 W in a PowerCab supplying 3A, if similar mosfets are used. I don't see any openings in the PowerCab for ventilation. (maybe I should cut some).
Im pretty sure that if you modify your power cab, operate it over the limit, NCE isnt going to warantee repair the thing.
Ive used mine for hours, as have many others, without exceeding the 2 Amp rated capacity.
Or just budget your current draw to 2amps?
Why all the fuss over three amps. The manufacturer states its a 2amp system. Dont exceed 2 amps and you will find that it will last you a long time.
To answer your question on the circuit breaker, typically they trip at the setpoint you choose. 2.5A = 2.5A. You can have a short that persists if you dont wire your layout properly.
Circuit breakers have what is called an instantaneous trip and a delay trip. Yes you can exceed the rated capacity for short periods. The idea being that you dont want small short (time) duration spurious conditions to trip things off. You do want it to trip instantaneously when a high inrush condition occurs (as in a short circuit). Typically "things" are designed to somewhere around 150% of their nameplate rating. This provides you with a margin to safety. Operate at the nameplate rating of the device, not the technological limit.
rrinker In the data sheet of power drivers and things like voltage regulators, there are specificatioons for maximum current, assuming a heat sinking capacity that is alsooo specified. Using less or no heat sink, the devices won't instantly fry, but they will be unable to deliver that same maximum power without failing. Combined with an enclosed plastic case with little or no ventilation, you can build up quite a bit of heat, certainly enough to melt plastic. 2 amps at 15 volts is 30 watts
this looks like the power dissipated by the load (the output is 15V, right), not the power circuit on the heat sink?
the power dissipated by a linear voltage regulator depends on the difference between the unregulated input voltage and the output voltage. If the input is 20V, the output 15V and 2A, the regulator is dissipating 10W.
rrinker Assuming they are using power MOSFETs for the H bridge driver.
if they are using bipolar transistors, the power dissipated depends on the saturation voltage across the transistor which is 3.0V for an 2n3055. This means 30W for each of the two active transistors in the H-bridge or 60W lost in the power circuit using bipolar rather than MOSFETs which would only dissipate 8W.
with this in mind, why wouldn't you assuem they are using a MOSFET in a high power h-bridge?
BMMECNYCOr just budget your current draw to 2amps?
i don't know exactly how much current my locos draw. I use a 1+A lamp for protection and short indication. I have a cranky boxcab that sometimes causes the lamp to glow.
i understand that circuit breakers don't trip immediately. The diagram below illustrates that a home breaker will trip faster depending on how far above the trip current the actual current is.
I don't want my PowerCab to shutdown immediately if 2A is exceeded unless it's a short (some max current limit). Maybe it should after a 60 seconds if it's 2.1 A.
i had expected the PowerCab to protect itself both from damage to the electronics, as well as from melting. I don't want to spend an additional $20 for a circuit breaker to protect the PowerCab from damage. I don't want to monitor the current meter on the PowerCab (maybe there's a way to specify the shutdown current). I did install a lamp similar to the NCE CP6.
again, all this discussion helps me better understand this equipment, its limitations, how to use it better and how to build my own.
Early on in my DCC pursuits, I purchased a RRampMeter to measure voltage and amps. Some guys complain about the price. Others just use a multi meter. Still others build their own. To me, the RRampMeter was the best DCC related purchase that I ever made. You need it, or something like it, to protect your DCC system.
gregci don't know exactly how much current my locos draw.
Wire a multivolt meter in series with a DC power pack on a section of track. Aligator clamps and a harbor freight MVM set to measure current are all you need for this (I used the Radio Shack verison of the kit multi-volt meter).
That will get you in the ball park..