Frequently Asked Questions


General

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575W Modular RC Power Supply

Can I combine multiple power supplies in series for a higher output voltage?

YES!  You can combine up to four (4) in series for a nominal 48 VDC.  Proper configuration is described in the User Guide.  You can also check out our Videos page to see how to do it properly.

Can I combine multiple power supplies in parallel for more output current?

YES!  You can combine up to two (2) in parallel for a maximum current of 94A.  Proper configuration is described in the User Guide.  You can also check out our Videos page to see how to do it properly.

Can I combine multiple power supplies in a combination of series and parallel for higher output voltage and more output current?

YES!  You can combine up to four (4) in a combination of series and parallel, in a 2S2P configuration.  Proper configuration is described in the User Guide.  You can also check out our Videos page to see how to do it properly.

Can I configure multiple power supplies together and power them from different household circuits?

It is not recommended that you power multiple power supplies from different household circuits if the power supply outputs are wired together for increased output power.  While it may work, if one breaker trips and the other does not only some of your power supplies will be powered which could result in an unsafe situation.

I don't understand the ground strap.  Do I have to use it?  Will it work without it?

The ground strap is a critical safety component in the system.  The power supply will operate without the ground strap installed but it is NOT SAFE to do so.  The ground strap ensures that the negative DC terminal is at the same voltage potential as the metal power supply housing which is tied to earth ground.  This is necessary to ensure your safety!

What could happen if I don't use the ground strap?

Let's say you have one power supply and you have removed the ground strap.  If you power it up and grab your trusty multimeter, measuring the voltage from the positive terminal to the negative terminal should measure close to 12 VDC.  Now you measure from the positive terminal to the metal power supply housing and you see 13 VDC.  Now you're confused so you measure from the negative terminal to the metal power supply housing and you see 1 VDC.  Now you're totally perplexed!  What's going on here?

What's happening is the positive terminal is designed to output approximately 12 VDC referenced to the negative terminal (i.e. the difference between the positive and negative terminal should be approximately 12 VDC).  This is actually working since that is what you measured.  The problem is the negative terminal has no reference which means it is "floating".  It could vary, though it is most likely to be somewhat close to the same voltage potential as the metal housing.  Originally the negative terminal of these power supplies is directly wired internally to the metal housing.  We remove that internal wiring on all units so that you can stack them together yourself.  However, you must properly use the provided ground strap in place of that internal wiring to ensure your safety!

Continuing with our example where you do not have the ground strap installed, you connect your charger to the power supply and it powers up so everything seem OK, right?  WRONG!  If that charger has a metal case (or any exposed metal component) that is wired to the negative power input of the charger this is an unsafe situation.  Set that metal cased charger on the power supply without any electrical isolation and ZAP!  Unintentional fireworks could fly as the charger housing is pulled down (or up) to the same voltage potential as the power supply housing.  Even worse would be if you grab the charger with one hand and the power supply with the other hand that ZAP will travel through you, also known as ELECTRIC SHOCK!  This is why it is IMPERATIVE that you properly install the ground strap.

Note that there is virtually no current that actually flows through the ground strap during normal operation.  It simply serves the purpose of providing a ground reference.  Without the ground strap, bad things can happen when you, the housings or some other object bridges that electrical gap but this is only brief as the voltage potential of the isolated circuits bridge together and equalize.

How many ground straps do I need when combining power supplies?

You should only have one (1) ground strap installed and the negative power wire of the load (i.e. black charger wire connected to the power supply) should always be connected to the power supply terminal with the ground strap installed.  You do not need more than one ground strap installed in a parallel configuration.  The ground strap does not carry any real current.  It only serves as a reference for the negative DC terminal.  All of the real current travels through the negative DC terminal into the power supply to complete the circuit.

A short lesson in electrical circuits...the rule is that current (amps) follows the path of least resistance.  However, this is not entirely clear.  What this means is that if current has the choice of 2 paths A and B, and path A has lower resistance than path B, more current will travel through path A than will travel through path B.  That does not mean that no current will travel through path B.  It simply means that less current will travel through path B.

Additionally, unlike voltage which drops across a load (think of your charger as the load and the voltage drops from +12V to GND across your charger), current does not drop from the source (+12V terminal) to the return (GND terminal).

Why the quick lesson?  This is important and I cannot stress the importance and purpose of the ground strap enough.   Let's say you configure two power supplies in parallel which means you have two jumper wires (one connecting the +12V terminals and one connecting the GND terminals).  Let's also assume you leave both ground straps installed.  Now let's say you have one charger pulling 94A of current from your two power supplies.  That means that your negative charger lead is only connected to one of the GND terminals, right?  So 94A of current flows through your charger to only one of the GND terminals, but that 94A of current needs to return as 47A to each of the two power supplies.  In this scenario, how does the 47A return to the GND terminal of the power supply that the charger is not connected to?  The jumper, right?  Well, some of the current flows through the jumper.  Remember you left the ground strap installed on that other power supply?  Now you have three paths for that current to return to that other power supply, two of which are via the ground strap.  So part of that 47A will flow from case to case (assuming they have electrical contact) and some of that 47A will flow back through the earth ground wire in the power cord of the power supply that the charger is connected to and up the earth ground wire of the other power cord, both paths completed to the negative DC terminal via the ground strap.  Since the jumper wire is much shorter and larger gauge than the power cord wire, more current will flow through the jumper wire since it has less resistance.  Additionally, the case of the power supply is coated so it will not make the best electrical contact, increasing its resistance.  Still, some current will likely flow from case to case.

Remove the ground strap from that other power supply and all of the current is forced to travel through only the jumper wire.  This is the best and safest method.

Are there any spacing requirements for proper ventilation?

You should not block the fan input on the DC terminal end of the power supply (binding post end) or the vent screen on the AC end of the power supply (power cord end).  A minimum clearance of 2" on each end is recommended for proper ventilation.  You can stack the power supplies horizontally or vertically without any spacing between the long sides.

Where's the power switch?

There isn't one.  Just plug it in!

Why isn't there a power switch?

We decided that adding a power switch would be a bad idea for a number of reasons.  First, it would increase our cost which would drive up the price of the unit.  Second, there is limited space to add a switch without modifications to the original housing which we wanted to avoid.  Finally, and most importantly, it is a potential safety concern for each unit to have its own power switch when combining units in series.

Are there limitations on how I can power these units?

Actually, yes there are.  Here are some examples, all assuming there is little or no additional load on the household circuit in each example.  In some cases special wiring may be necessary in your home.  You should always consult a local electrician for any changes or additions to your electrical system.

Up to 2 units can be powered from a standard 120V 15A circuit.  This scenario is similar to running your typical household vacuum cleaner.

Up to 3 units can be powered from a standard 120V 20A circuit.  Note that if you fully load the 3 units on the 20A circuit you might trip the breaker but you should be able to get pretty close to full load without issue.

More than 3 units will most likely require a special circuit in your home.  For example, 4 units can source up to 2300W of power.  Using the standard 80% rule for loading household circuits (continuous load should not exceed 80% of the breaker rating), maximum load on 4 power supplies will require a circuit that can handle over 2800W of power.  A standard 120V 20A circuit is a maximum of 2400W of power (1920W of continuous power based on the 80% rule) which is insufficient to power 4 units at maximum load.

We do not recommended that you power 4 supplies from 2 different household circuits unless the breakers for the 2 circuits are mechanically linked to ensure that if one breaker trips the other will trip with it.  If you power 4 units from 2 different circuits that are not fed through mechanically linked breakers it is possible to trip one breaker and not the other resulting in an unsafe situation.

If you would like to run more than 3 power supplies together, please consult your local electrician.

How efficient are they?

They are approximately 80-86% efficient depending on the load.  We did some load testing and calculated efficiency all the way up to a 54A load (yes, that is beyond the spec, and note that they will go into over-current protection at 55A load).  You can find the test results here.

I noticed threaded holes in the ventilation mesh on the AC end of the power supply.  Can I use these holes?

YES!  There are 2 threaded holes on the AC end of the power supply (power cord end).  These holes are size M3 with 0.5mm pitch.  Installed screws should not thread deeper than 4mm into the hole.  Below are images that highlight the holes and an example of how you might want to utilize them.  Click on an image to enlarge.

Threaded Holes

Example - Securing Power Supplies Together

What configuration do you recommend for my battery charger?

We have received this question numerous times so we have compiled a table of all FMA/Revolectrix and Junsi iCharger battery chargers and recommended power supply configurations for each.  You can download the PDF here.  If your charger is not in the table, feel free to send an email to support@2zo-rc.com.  We will be happy to analyze the specifications of your battery charger and recommend a power supply configuration to match it.