Printer Friendly Forum Posts - draining battery

What happens with an amplifier and /or speakers when the system is played at maximum performance but with the car switched off, ie. the battery does not get charged - battery voltage lower and lower. will the amplifier's power supply get damaged due to inconsistant battery supply, will the amplifier start to clipp the signal where it didn't before? Just need some expert opinions. Had an amplifier to repair recently and was told that it was played with car switched off.

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Marius Minnie

It depends on the amp.

I used to have a Kicker ZR600 that had a fully regulated power supply (made the same power at 12vdc as it did at 16vdc).

However, once the voltage started dropping the amp would pull more current to compensate. If the voltage got too low it would blow the 3 30A fuses in the side of the amp. As long as battery voltage remained high I didn't have any problems.

Different amp manufacturers use different power supply technology. It is very possible that a low or unstable voltage damaged your amp. Instead of asking us if it is possible you should be asking them exactly what parts they replaced and why they think fluctuating voltage caused the problem.

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Kevin Pierson

It was a Camtec MIG1500 (not a known brand in the states). The amplifier has an unregulated power supply and therefore I suspect that the cause could have been due to insufficient battery power.
The power supply PCB is destroyed, even melted the heatsink plates/aluminium brackets clamping the fets to the heatsink. I will try to load the pictures on the web.
Can you explain how a power supply reacts in the case of draining battery power?

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Marius Minnie

Here is the link to the images. posted_image

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Marius Minnie

www.freewebs.com/autoaudiorepair/mig1500.htm
Sorry

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Marius Minnie

There are too many variables in a power supply to guess. How low was your battery voltage getting?

It may be possible that the supply voltage was falling below the minimum operation voltage for some of the components, which could effect their operation. It's really hard to say. If it is a voltage related issue, and you say the circuit board is melted, I would think that the voltage would have to be really low for a long period of time to create enough heat to melt the board, unless there is evidence of a small fire.

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Kevin Pierson

I have no idea of the actual voltages at the time, but for arguments' sake lets say the system was set up with a voltage of +/- 13.5V. If it was played for a period of time without the engine running, with the voltage going down to about 11V-10.5V, what could happen? (This is a 3000W max / 500W RMS, one channel, class AB amplifier. The owner connected 2 x SVC 800W Kenwood subs = 2ohm load with apparently only 8guage power cable.) Did you have a look at the pictures?

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Marius Minnie

No, I could not load the pictures for some reason.

Again, it is hard to say how it will respond at lower voltages. Typically, in a non regulated power supply you're output power will drop as your input voltage drops. I wouldn't expect that to damage a quality amplifier though.

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Kevin Pierson

I know that the old Orion HCCA amps were unregulated and if the voltage got too low they would fry...they could handle high voltages though but they didn't like anything lower then like 12 volts for too long

I'm looking for a technical explanation for what happens inside the amplifier when the voltage gets too low. My explanation is as follows; let me know if this sounds logical: The "Orion" amplifier is set up for maximum performance at a voltage of +-13.5V. If the voltage drops (the output rail voltage will also drop) then the amplifier will start clipping the signal, which means that the power supply will have to supply more current at a lower supply voltage. The power supply FETS will overheat and burn out.

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Marius Minnie

Unregulated power supplies are usually set at 50 percent ('ON' 50 percent of its timing cycle) and don't suffer from lower voltage. A regulated supply will try and compensate for the lower rail voltages and increase the 'ON' time which as csound stated increases the current and heats up the mosfets. The heat protection circuit is 'supposed' to shut the amp down before damage occurs, but more often than not, it doesn't. I had someone bring me an old Coustic 380 to repair that had an output transistor shorted out. This amp got so hot that the paint bubbled-up and the protection circuit never shut it down, nor did it blow the 30a. fuse.

Just curious. Wouldn't low voltage cause the remote on lead to shut the amp off?

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There is no such thing as free installation!

If it is agreed that the power supply will have to supply more current when the signal is clipped, then it doesn't really matter whether the power supply is regulated or not. Still more current has to flow and causes for heat generation and eventually breakdown.

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Marius Minnie

An unregulated PS is 'usually' running on a 50 percent duty cycle and will/should handle more load due to the constantly drained rail capacitors. Its the regulated PS's that will suffer the most. Yes, unregulated PS will run hotter due to lower supply voltage, but my experiences lead me to believe that they survive low voltages better...within reason.

Thank you "dboomer". Seems you have enough experience with amplifier repair. Please have a look at the pictures on the link below. (you have to copy and paste into your browser)
What could have caused this damage to the power supply? No obvious reasons inside the amplifier could be found. This amplifier has a dual power supply and both went up in smoke. No output transistors were blown.

www.freewebs.com/autoaudiorepair/mig1500.htm

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Marius Minnie

How many ohms are your speakers drawing? Ususally damage to both supplies is caused by running to many speakers wired in parallel. The weakest mosfet will short out internally and take-out the others. Also check your rail capacitors and rectifiers for shorts. It doesn't take much of a load/short in the secondary winding of the transformer to make a huge load in the primary and may not show any signs of damage.

2 x SVC 800W Kenwood subs = 2ohm.
The amplifier is 1ohm stable. Both torroidal transformers are secure and OK, dual diodes and caps tested OK.

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Marius Minnie

A bad ground could also be a possibility. I would suspect the draw from the 2 ohm speakers caused the 'meltdown'. 2 ohms is hard an amps ... even if designed for it.

In my uncles shop we have 2 amps and a stereo hooked up to a battery there to test speakers/ equipment or to show people how some speakers sound. When the battery gets low the equipment just starts to shut off and we disconnect the fuse to the amps and stereo and charge the battery again, when its charged we reconnect the fuse and its ready to go. The amps have been connected for like a year or so and we never had any problems with melting parts or blown fuses, the amps that are connected are a power acoustik and a hifonics.

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THE DUCE

It could be that steezs' amps have low voltage protection, looks like the acoustik and hifonics
brands are manufactured by reputable companies. This amplifier was manufactured in China and, as far as I know, does not have any low voltage protection. I think that the poor ground that dboomer mentioned is a definite cause for power supply failure but it was not the cause in this instance. I had a look at the power cables in the clients' car, it is wired with 4guage cable (power and ground) with good, clean connections. So, to get back to the original question, can the power supply be damaged by fading battery power (amp without any low voltage protection), taking into consideration the load and initial setup voltage?

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Marius Minnie

I would suspect the PS couldn't handle the 2ohm load on the output. Your pictures didn't show the output transistors. How many pairs are there? There is generally 2 PS fets for every output pair. With 8 PS fets you should have a maximum of 4 pairs of output transistors per channel. Also considering its made in China, the PS transistors and output transistors may not be properly matched...they may have stuck whatever was cheapest and readily available.

The one channel amp has six output transistors on the "P" side and six on the "N" side (class AB). With eight FETS per power supply (Dual power supply).
The amp is rated 1ohm stable by the manufacturers. How do they "match" power supply and output transistors? Do you mean that the IRFZ44 FETS can't handle the current that the output transistors can = 2SC5200 and 2SA1943.

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Marius Minnie

That would mean a 2.4:1 ratio (2.4 PS fets to each output pair (1 NPN and 1 PNP)) which would be good for a 4ohm load. I am guessing that the output is probably working off 50 to 60 volt supplies (pos and neg). That means the transformers would have a 4.5 to 5 turn ratio putting tremendous load on the Z44’s. Z48’s would have been a better match. I believe they over rated the capabilities of this amp (as with most amps). If you wanted to repair this amp (if the board is not charred too bad) and run a 2 ohm load, I would install Z48’s. They handle more current and I have had success in interchanging them without altering the circuit. Although I guarantee nothing…lol.

I did some calculations on that amp. It produces 750 w/rms at 2 ohms so take the square root of 750x2 which equals 38.7, then multiply by 1.4 to get peak voltage 54.2, then multiply by 1.25 to compensate for efficiency loss(output stage only, which can even be higher depending on the circuit) now your around 68v or higher that the PS has to produce. Now divide 68 by 14.4 (battery voltage which could be from 12 to the 14.4 that I generally use) and now you have the transformer turns ratio of 4.7 @14.4v or 5.6 @12v. Now we need to figure the amperage of the output stage. Take you 750w / 68v and your at 11 amps. Multiply 11a x 4.7 and then compensate for efficiency loos of the PS of 1.2 and your at 62 amps of 14.4 volts. Now divide that by 16 (the number of z44's) and you have each one having to produce 3.9 amps. Multiply 3.9 by 14.4 and your at 56 watts per fet. The data sheet shows that these fet will dissapate 94w cold and only 50w warm. And considering that there are 16, the chances of one being weaker than the rest is quite high. I would say this is/was a great 4 ohm amp but not a 2 ohm. Also take into consideration that these figures are at 14.4v and very high effifiency, actual load on the fets are probably much higher. Hope this helps.