The most common questions and answer.

Q: Fuse dimensioning?
A: Please read the manual supplied with your ordered DC/DC converters. You can also download the installation manual.

Q: Input protection?
A: In general we do not supply our converters with a fuse, for two reasons. The first, fuse specifications vary between applications on dc voltages. The second reason is that on DC distribution networks the fuse to the DC/DC converter should be at the distribution point, to protect the cables from short-circuits. All types have a parallel diode or series diode to protect against input reverse voltages. The parallel diode is only designed to blow an input fuse.

Q: Inrush current?
A: On the input side there is an inrush current or start up current produced by the charge of the input capacitors. The level of inrush current depends on the feeding system impedance and voltage. Therefore we cannot give a value of inrush current. The main problems with inrush currents are the fuses and fuse characteristics.
To limit the inrush current you can order NTC resistor as an option. On the PSC600 and PU1000 we have active current limit on 110 and 220 input code. For 48V this is optional. On PC1000, PC1400, PC2000 series the inrush current limit is standard on all inputs.
The PSC600 and PC1000, PC1400, PC2000 has very low inrush current <Inom.

Q: Hold-up time?
A: On DC-input units a long hold-up time is only needed where two battery systems are switched between. To improve hold-up time a series diode and larger capacitors are needed on the input. Please contact us for further information.

Q: Can I parallel connect a DC/DC converter?
A: Yes you can connect all Polyamp in parallel. It is recommended to use a series diode on the output to isolate any fault. There are two major reasons to connect in parallel:
1. To achieve more power than contained in one unit.
By connecting two or more units in parallel you can achieve high power systems. As Polyamp can supply converters up to 1000-2000 W it is usually suitable for very large systems.
2. To get redundant operation N+1.
If you need a very reliable power system, two converters or more can be connected in parallel. Each converter is then specified to carry the whole load or you have an N+1 configuration. The converters must have series diode and output alarms to provide fault indication in case of failure. For more information how to connect and precautions download the installation manual. (Länk till download) on the model you intend to use.

Q: Load fusing?
A: If you supply a single load our current limit is faster than a fuse. If you supply several loads then you shall fuse them separately. For more details, please download the installation manual on the model you intend to use.

Q: What is current limit?
A: The current limit is there to protect the converter from excess loads that would overheat or destroy the converter at short circuits. Most of our converter has a rectangular current limit. It means that the output voltage decrease quickly at excess loads, but the output current still remains. We usually set the current limit at +5% above the max rated current. Another current limit type is called fold forward, where the current is increasing at short circuit. A third model is fold back current limit that decrease the output current or come in to a start and stop mode. It start and realise the output is short circuited and stop again about every second. This is used on PM50/PM80. On higher output power start currents from the load can be large and a fold-back characteristic can cause start problems.

Q: Remote sense?
A: Sense is used when you want to improve the regulation at the load. The voltage regulation of the converter is put at the load and not at the output of the converter. Use twisted pair cable. With long sense leads a screened cable is recommended. See figure 4. We have remote sense on high-power units from 300W and up, as the output current is high and sense may be required. The PSC series has sense as an option. IEC1000-4-6; 0.15 to 30 MHz current injection with AM-modulation can cause interference on the output only when remote sense is used. If shorter sense less than 3 meters are used this test does not need to be performed.

Q: Efficiency?
A: We specify efficiency at 100% load and at the extreme of our input voltage ranges. The efficiency depends on input voltage range, input and output voltage and conversion topology. In general our 3:1 input voltage ranges have 84% ±4% efficiency and limited input ranges have 90% ±2% efficiency.

Q: How to load / How to cool?
A: Our converters are specified and tested to work at a full ambient temperature range of -25 to +55°C or +70°C at 100% load. Continuous operation at high ambient temperatures cuts the life expectancy of the unit. Some customers derate to spare their units, to less than 50% of the rated load capacity.On a well designed converter the ambient temperature is more important than the load, in achieving long life expectancy. As our converters are cased in closed aluminium boxes and dimensioned for convection cooling it is very efficient to arrange a small air flow around them. A 10°C lower ambient temperature will basically doubles the life expectancy of the unit. A general feature of a Polyamp converter is that it is relatively cool at full load. Consult Polyamp on general thermal management questions for your application.

Q: EMC?
A: A Polyamp has been tested for low emission meeting commercial and domestic environments. This means level B on EN50011 and EN50022 or FCA xxxxx. The immunity levels are higher than the industrial levels.

Q: Product standards?
A: Different industrial sectors have Product standards. Power supplies and DC/DC converters (PSUs) product standard is the IEC/EN61204. As a PSU is a generic product in many applications customer constantly ask us to meet there product standard. Most product standards follow the generic standards on EMC with few exceptions. With IEC/EN60950 safety standard most PSUs meets most other safety standards.

Q: CE mark?
A: The CE mark for a self standing DC/DC converter means EMC and Electrical safety. Most of our competitors specify CE mark without correct reference to the standards required. You should be suspicious then. Our CE mark is worth more than the label.

Q: Installation problems?
A: Download the installation manual of the model you are using.

Q: Warranty?
A: We give warranty of two years from delivery. Our warranty is valid if you return our unit within that period. We repair or replace the unit without cost. Please contact us in prior to return.

Polyamp AB
Box 229
SE-597 25 Åtvidaberg, Sweden
Tel: +46 120 854 00 Fax: +46 120 854 05

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