Controller electronics question

[ZooT]

I've built a very rustic dump controller here using a zener diode, a few regular diodes, a capacitor, and a NPN power transistor, and it works fine, but isn't very useful because the power transistor won't handle enough current to use anything larger than the "12 volt heated coffee cup/12vdc muffin fan that cools the transistor heatsink" that I'm using for a dump load right now.

The power transistor is a MJE3055 transistor(that radioshack sells as a TIP 3055) that's supposed to handle something like 60 watts, but if I can I want to use the "real" TIP 3055 transistors that I received via fedex the other day

Now the question,

If I gang up two power transistors and connect them base to base, collector to collector, and emitter to emitter, and use them in place of a single power transistor, will this increase the current handling ability of the controller so I can use a bigger dumpload, and make the controller more useful?

Still taking tiny steps......but I'm learning 8^P

[Kevin L]

Yes you can run in parallel, but why use transistors.  Unless you are switching all the time, a simple relay should work fine for small currents like is used in automotive.  Most headlight and RR Defroster relays are rated to 30 Amps. If you really want to use a transistor choose something like this that can be purchased here.  This unit is good to 75 Amps @ 60 V with a 225 peak surge current rating.  

Kevin L

[Kevin L]

The MJE3055 transistor data sheet here and the TIP3055 transistor data sheet here show the TIP to have a current rating of 15 Amps vs 10 Amps from the MJE, so you wont be gaining to much from the change if you are looking for a large increase.  Just FYI if you don't already have the datasheets.

[Flux]

You don't give much information to go on. Is this switching or is it a linear dump regulator?

For switching the Tip3055 may be reasonable. For linear operation it is a pretty poor choice compared to a decent hometaxial 2N3055, the planar versions are not so good for linear but for your needs you will not see second breakdown ( don't worry if this means nothing to you, not all 2n3055's are made the same way).

As a linear regulator the 2N3055 is a bit limited, I prefer 2N3771, but you can make small dump regulators with one device. For higher power you need more in parallel, but just connecting the 3 leads directly together gives you little gain as they will not share current unless you do something to force them, such as include resistors in the emitter or base circuits.

If you are trying to switch then mosfets are far better, but if you have heat sinks available at low cost then bipolars as linear dumps work very well and don't have the radio interference problems associated with switching pwm.

2N3055 is limited to about 60W per device, with practical heat sinking, but if you choose a suitable series resistor you can dump 240W as the dissipation in the transistor is 25% with half volts across the resistor. Avoid the Tip3055 for linear regulators, the don't like handling much of their claimed 90W rating.

Flux

[Opera House]

Do you want to waste heat or transfer that energy to do something useful?  When you parallel transistors, a small value resistor must be placed in the emitter (0.1 ohm)to balance the gains of all the transistors.  Typically, you will need to use one transistor to drive the others emitter to base in a darlington configuration.  

Separate collector resistors on each transistor can also be used.  This will guarantee a known load for each transistor.   If you don't want to wast this energy, look into using a PWM chip like TL494.  They can be found in many old computer power supplies.  I posted a dump load a while back made from one.  It could use your 3055's.

[thirteen]

I will be switching maybe three times a year at the most. When the water is to low or if it freezes up during the winter. The rest of the time the solar panels will be off or covered. I would be able to redirect my solar panels for the 2 to 3 hrs of sunlight I get during the winter if needed. 1 hr in the morning then 2-2 1/2 in the after noon. I have a mountain in the way. I will look at both items suggested. Thanks  

[ZooT]

Well folks.....Thanks much for the replies

I'm going to have to let it all digest for a while, as from what everyone said, when mixed and blended.....I think I might have enough to get it dumping something useful.

[ZooT]

Flux,

I'm a bit cloudy on this statement.

Quote:

2N3055 is limited to about 60W per device, with practical heat sinking, but if you choose a suitable series resistor you can dump 240W as the dissipation in the transistor is 25% with half volts across the resistor. Avoid the Tip3055 for linear regulators, the don't like handling much of their claimed 90W rating.

I'll post a pic and ask if the resistor in this circuit is a "series resistor" and/or a resistor in series with the collector.

[Lumberjack]

solar panel? dump load? If my admittedly bad memory is working solar does not need a dump load per say....you can simply leave the output open.