I don't know what forum this would go under so I'm posting it here.

Jstas

I'm looking for a new workbench power supply. I currently have a Pyramid power supply that is 13.8V but only 10 amps. It worked great for my RC Car battery charging needs but, it's broken. So I wanted to replace it with something closer to say 13-15 amps. Pretty much an AC power supply with 13V out at 15 amps.

I found this Pyramid one for an OK price:


Output: 13.8V DC
18 amp constant, 20 amp surge
Input: 115V AC, 60Hz, 450 watts
Electronic overload protection w/auto reset
Crowbar over-voltage protection
Short circuit & thermal protection
Fuse protected
LED condition indicators
Screw terminal connectors
Built-in cooling fan
Heavy duty cabinet & heatsink with anti-skid rubber feet
Dimensions: 11.81" L x 9.05" W x 4.92" H


For about 100 bucks. The reason iwant something so powerful is for running automotive audio gear without having to install it into a vehicle or hooking it up to a car battery. Car batteries are unregulated and a very spikey power source. Hooking car stereo stuff up to one directly is just asking for problems. However, I do have a need to test and run car audio gear outside of a car and the only way I can think to do that is to run a unit like the one above. Unless I build my own but the transformer I would need would run me about 50 bucks plus all the other parts I would need would push me over the 100 dollar price for this unit.

Does anybody have any other suggestions or companies making these kinds of units?

HBombToo

Originally posted by Jstas
Car batteries are unregulated and a very spikey power source. Hooking car stereo stuff up to one directly is just asking for problems.

I can't offer up much help here but I'm do have a question regarding batteries being unregulated and spikey... Can you help explain this?

HBomb

Jstas

Originally posted by HBombToo


I can't offer up much help here but I'm do have a question regarding batteries being unregulated and spikey... Can you help explain this?

HBomb

Car batteries are not regulated because they do not have anything on them to regulate the discharge. Hence the need for a voltage regulator in a car or on a car battery charger. A battery is just that, a battery. It's a series of lead or zinc plates suspended in a sulfuric acid solution, that holds an electrical charge when an electrical current is passed over the plate system. That's basically it for a battery.

Since batteries work on the flow and exchange of electrons, they do not discharge at a constant rate. Hence the reason it's harder to start a car when the battery is going bad or why your portable CD player amp begins to clip when you need new batteries. Discharging batteries slowly lose the voltage and amperage base needed to support the current draw.

Since it is not done at a constant rate and a cell inside the battery could go bad or have a solution to plate ratio that isn't ideal, it will not support the same ccharge levels. It may be higher, it may be lower. Also, foreign things like water, dust or other stuff, even human hair, can cause a current draw that takes away from the battery's ability to support its load.

It is a good source of long term power and storage but as far as stability goes, it's one of the worst. Also, an unregulated battery can discharge rather quickly. In addition, a battery is unsafe for use indoors. While charging and discharging, your battery gives off gases that are extremely poisonous to anything living, including plants. So a car battery is not the best deal for powering anything other than a vehicle with a regulated charging system.

I hope that answered you question. If I wasn't clear on something, let me know and I will try to explain it differently.

wlrandall

Originally posted by Jstas


Car batteries are not regulated because they do not have anything on them to regulate the discharge. Hence the need for a voltage regulator in a car or on a car battery charger. A battery is just that, a battery. It's a series of lead or zinc plates suspended in a sulfuric acid solution, that holds an electrical charge when an electrical current is passed over the plate system. That's basically it for a battery.

Not to start a war but I absolutely totally disagree. The regulator is in the alternator-to regulate the current and voltage while charging the battery-not to regulate it's output. Lead/acid batteries are by and far the most stable power source available, sweet and simple, just as you indicated (plates and acid).

After years of problems with DC power supplies on 50+ test stands we actually considered using batteries. We shot the plan down because of the fume issue.

Put a chart recorder on a battery and see how stable it actually is.

Wally

Jstas

I've done this before. I've seen the results. Your reference is valid only for a brand spanking new battery. I've tested many car batteries and alternators. I've charged many more. I've seen how unstable they can be especially in a car.

I'm not going to go into how the charging system of a car works here because that would be totally not what this forum is about. DC power sources are notoriously spikey, whether it is a battery or not. I would prefer to use a fused DC power supply on a circuit breaker rather than having to constantly recharge a battery.

Go back to your battery with your chart recorded. This time, put a load on the battery and watch what the amperage does. Take a look at how low the voltage drops. That won't happen in your car because of the alternator and the voltage regulator. Your alternator is capable of providing enough juice to both run your car and charge your battery at the same time.

HBombToo

I'm probably missing something here but I always thought of a battery as the most stable potential available... I just don't understand I guess. Question is how can a +/- type voltage variations occurr? I can see a battery lose potential as use without recharge, but how can it swing?

I do know the fumes your referring to in a lead acid battery is hydrogen and can cause serious problems if exposed to a flame or even sparks. KA BOOM! goes the room if not properly ventilated and large battery rooms for telecom centers even have huge exaust fans to prevent this from happening.

HBomb

Jstas

You are talking of UPS batteries which are not the same as an automotive application. Automotive batteries, unless they are deep cycle, discharge rapidly for a battery. They produce alot of amperage quickly because of high demand things like starting the car. Other batteries do not have that kind of load and can support higher current draws for long periods of time. Other batteries are very stable sources. A car battery is not. A car battery under constant heavy load can not only release poisonous and flammable gases but they can explode or boil over. Especially if they discharge completely. I used to work in an automotive repair shop. I've handled, tested, charged and troubleshot many different charging problems. I've seen car batteries do things that other batteries don't. In most cases, they can be very stable but the instant something isn't right, cells fry, resivoirs boil over or they explode and cause thjousands of dollars worth of damage. I've seen batteries explode left on a trickle charge overnight. They are not a good choice for a workbench power supply.