You can use the following guidelines in selecting a power supply best suited for your needs.
Selecting the right power supply is an important step for optimizing your molecular biology work in the lab.
A well-designed, and well-constructed power pack can last a lifetime. |
The aim while deciding which equipment to buy should be - to procure the best that your laboratory would need, without spending too much for an equipment which is filled with features that you may never use.
Some of the important points for selecting a power pack are given below. 1. CV/ CC auto crossover CV - constant voltage, CC - constant current,
auto crossover - ability to switch automatically between CV and CC There are two types of power supplies available for use in biology labs.
1. CV power pack2. CV/ CC auto crossover power pack.
The first step is to determine which one of these you require. A CV power pack will only be able to run at constant voltage, and hence cannot be set to run at a constant current. A CV/ CC power pack can be set at constant voltage as well as constant current but is expensive due to the technology used. Auto-crossover is the feature which helps to keep the gel running when the voltage or current limit is reached by automatically switching to the other mode.
For e.g. Let's say, you are using a 300 V, 100 mA power pack to run a horizontal electrophoresis apparatus and have set it at 150 V (i.e. at CV), and the current passing through the unit is 90 mA. With time the current will increase due to the change in buffer composition. As the current limit of 100 mA is reached, the power pack will either switch off or start to heat up and burn out (depending on the type of power supply). If instead of a CV power pack, you were using an CV/ CC auto-crossover power pack, then, once the current limit of 100 mA is reached, the current will become constant and the voltage will decrease. [keeping in mind Ohm's law, V = I R, i.e. voltage = current x resistance] Most gels are run at constant voltages; but many researchers run their vertical format gels at constant currents. Hence, you need to decide what mode you would be running your gels. If you need only constant voltage and you have a budget constraint, then opt for a CV power supply, else, opt for a CV/ CC auto crossover power supply. If you are not sure which power pack you should opt for, please contact us (at firstname.lastname@example.org) for clarifications.
All TechnoSource brand power packs have CV/ CC feature with auto crossover whereas EcoSep brand has CV power supplies.
2. Accuracy How accurate do you need the power pack to be? Accurate power packs are expensive due to the technology used. Some power supplies can have accurate regulation up to 0.1 % of the displayed voltage/ current.
If you need a power supply for use in demonstrations of experiments, you would probably not need a very accurate power pack, whereas, if you are doing cutting edge science then repeatability and accuracy is of utmost importance, and you should probably opt for a highly regulated power pack. For e.g. a blot that was transferred for 12 hrs. yesterday at 100 V, gave great results. What if, today the transfer was performed at 100 V, but, you observe that the large molecular weight proteins have not transferred completely? If your power supply is accurate you can be assured that the voltage was not the reason for the failure to transfer. But, what if the power supply (due to inaccuracy) was set to 100 V but was actually at 90 V? These type of non-accurate power supplies are quite common in labs; and you will be surprised at how many power packs are not accurate even to 10 % of set voltage, i.e. the actual value of the voltage could be 115 V when it has been set to 100 V. All TechnoSource brand power packs have voltage regulation better than 0.25 % under no load to full load conditions. That means that when set to 100 V the actual voltage will be within the range of 99.75 V - 100.25 V, whether you have a very small vertical apparatus running or a large blotting system.
3. Number of Outputs Having a larger number of outputs is generally better as multiple units (gel or blots) can be run at the same time. Just make certain that the total current consumed by all the units, that you plan to run simultaneously, does not exceed the current limit of the power supply.
Our TechnoSource range power packs have four outputs in parallel. They can be customized to have more outputs.
4. Display The display is used to indicate the voltage and current. In some power packs they also show the countdown timer. Many power supplies have a single display which shows either voltage, current or countdown time and have a toggle switch to choose what to display.
- Having a separate display for voltage, current and time is preferable as, at one glance all three can be seen. If there is an issue with the voltage set, or current drawn, or timer set; it can be immediately noticed and rectified. - Larger displays are preferable over smaller displays as the readings can be noted from a distance. - LED displays are brighter and can be seen from afar. Hence, they are better than LCD displays. Also, LED displays are economical to replace if required.
5. Operating temperature range
The operating temperature range refers to the range of temperatures between which the power packs can comfortably run continuously (for weeks or months) without heating up, burning out,
or causing any long term damage.
Most power supplies have an operating temperature range between 20-40 °C. Well-designed power packs can have operating
ranges of 0-50 °C.
Some power packs are specially made to sustain continuous operations in cold rooms, cold cabinets, fridges etc.
These can withstand temperatures of -10 °C.
Where are you going to use the power supply? If the power pack is only to be used in a lab equipped with an air-conditioner then any of the above will do.
But, if the temperature in your lab varies with the season, or you need to put the power pack in the cold room, then the one with the larger range is preferable.
Some power packs are equipped with a fan to take care of the internal heat that is generated due to inefficiencies of the power supply. This is a
simple and effective way to increase the temperature range of the power supply, but, if such a power pack
is placed in a cold room or a cold cabin, it will start affecting the performance of the cold room/ cabin, as it will start building up local heat.
When opting for a power supply, look for self-cooled units as they are more efficient. These can also be placed within a cold room or cabinet and will not affect performance of your cold room/ cold cabin.
6. Fans for cooling Most low end power supplies are equipped with a fan for expelling the excess heat generated due to inefficiencies of the power pack. Even some high end power supplies tend to be inefficient and need cooling via a fan. Many companies give a positive twist to this inherent problem and call it a feature! Having a fan means that there is excess heat to take care of, and this kind of power pack will put unnecessary load if placed in a cold room or in a cooling cabin. Even if you do not plan to put the power supply in a cold cabin, a fan is an unnecessary moving part which will need replacement when it wears off. Most well-designed power supplies will not need any moving parts and hence will probably function for years together without giving any problems.
7. Timer A timer can be a handy feature in your power supply. For e.g. You could set a timer for your blotting unit to make sure it switches off and does not over transfer your blots. If you plan to run only gels then you may want to rethink if the timer is a feature you will use. Units with a timer may be slightly more expensive that those without. Also do keep in mind that it is an additional part which could malfunction at some point in the life of the power supply. 8. Material of the chassis The chassis (or the body) of the power pack is responsible for maintaining its integrity and avoiding accidental contact to the electrical parts. The common materials used are plastic or metal. Metal chassis can be of aluminum or MS (a type of iron alloy). Each of them have their advantages and disadvantages as shown in the table below.
All our TechnoSource brand power supplies use aluminum chassis with a plastic front panel. This combination ensures that our power packs get the best of both worlds, as they have all the advantages of aluminum combined with the advantages of plastic. Our EcoSep brand equipment have plastic chassis and are light-weight and inert to spillages.
Summary 1. A CV/ CC power pack is better than a CV power pack 2. Buy an accurate power supply if you are doing research 3. A power pack with more outlets is better as you can run more gels 4. Independent voltage, current and timer displays are preferred
5. A larger operating temperature range helps 6. Buy a power pack without a fan if possible 7. Opt for a timer only if you need one
8. A power supply body made of aluminum and/or plastic is better
Is a high wattage power supply better than a low wattage power supply? Or is it the way around?
A common misconception is that a higher wattage power supply will consume more power and thus will be expensive to run due to the
increased electricity consumption. This line of reasoning is faulty as it assumes that wattage is an indication of how much power is
continuously consumed, whereas, it is only an indicator as to how much maximum power could be delivered.
To understand this better, lets talk about an analogous situation where you are looking to buy a car.
The two options available to you are; a car with a top speed of 120 km/hr, and another with a top speed of 80 km/hr.
Some questions you may want to ponder over before making the decision;
- Would you want a car which can go to 120 km/hr, when required, or a car which can only go to 80 km/hr.
- Does having a car which goes to 120 km/hr mean it always has to run at 120 km/hr.
- If you were writing the specifications for a car you want to buy, would you not write "should go at least up to 120 km/hr"
rather than to write "should not go beyond 80 km/hr".
Similarly, when you specify that the power supply "should not go above 80 W", you are limiting your output.
Rather you should be writing "should deliver minimum 120 W". |
This analogy can be better understood when the concept of wattage is clarified further. What exactly is wattage and how is it calculated for a power supply? The term wattage is used colloquially to mean electrical power in watts. Electric power is 'W' when a current 'I' consisting of a charge 'Q' coulombs every 't' seconds passes through an electric potential difference of 'V' Wattage = work done per unit time = VQ/t = VI (As I = Q/t) i.e. Wattage = Voltage x Current E.g. 120 W = 300 V x 0.400 A (0.400 A is 400 mA) When you run your gel at 100 V and the display shows that the current is 50 mA, the wattage can be calculated by
100 V x 0.050 A = 5 W. This means that; whether you have a power pack which goes to a max. of 120 W or 80 W; the wattage consumed at this moment is 5 W.
If you run your power pack at 300 V and the current is 267 mA, the wattage is|
300 V x 0.267 A = 80 W. At this point, the maximum output of a 80 W power pack is reached. Hence, even if the specifications say that the power supply can go to 400 mA, in the current scenario, it will not go beyond 267 mA. If you run your power pack at 300 V and the current is 400 mA, the wattage is
300 V x 0.400 A = 120 W. This power pack is now functioning at the maximum limit if it was a 120 W power pack. Hence, a quick way to calculate the maximum wattage of a power supply should be to multiply the max. voltage possible with the max. current possible. But, many new power supplies do not seem to follow this principle. The wattage, does not seem to be a function of the max. voltage and current. This is because of the way the power supply has been configured. To keep the power pack light in weight; the wattage is kept low. But the drawback of doing this is that you can never achieve the maximum current and voltage at the same time. Why are TechnoSource power supplies better than many competitor power supplies? (w.r.t. the maximum wattage) All our power supplies are linear power supplies. i.e. their wattage can be calculated simply by multiplying the max. voltage and max. current. Our power packs have higher wattages than most of our competitors, which as we have explained earlier, is a good thing. Hence you can run more gels, larger gels or more blots at the same time. For e.g. On our power supplies rated at 300 V, 400 mA the wattage is 120 W. Here you can run two blots at 250 V, each consuming 200 mA; simultaneously. 250 V x (0.200 + 0.200) A 250 V x (0.400) A = 100 W You can run four vertical apparatus at 300 V, each consuming 100 mA; simultaneously 300 V x (0.100 + 0.100 + 0.100 + 0.100) A 300 V x (0.400) A = 120 W If you have any queries regarding power supplies and their use, please call us on 09819095429. We would love to help you.