I have a dual amp setup (one on each side of my Miata trunk). Both amps get power directly from the battery post. One amp (Memphis ST3004) grounds where the battery grounds (chassis), the other (Majestic 120W 4ch) on chassis on the other side. The remote turn-on lead goes from the harness to the first (Memphis) amp and where it is tied into that amp, I tied the remote turn on from the other amp (Majestic). What first raised my suspicions was that there was a spark when I put the fuse into the power lead for the Memphis amp. I then noticed, that when the speaker wires touch (I mean the blank ends during installation), it engages the safety circuit of the Memphis amp. Also, I get a loud thump from the speaker powered by the Memphis when I plug the empeg into the harness. Lastly, the green power diode was glowing even when the empeg wasn't in the sled (but I understood the manual to say that that was normnal).
Now, a week later with no movement of the car, the battery is drained. What could I have made wrong? Does that sound like some common mistake that happens to a lot of people?

Sounds like that amp is always on... I doubt that the green LED should always be on - most amps (can't comment on you specific one as I've never even seen one) will use that as an indicator that the amp is on - and that would/should only happen as the amp remote turn on wire is high.

Try disconnecting the remote wire from the amp, plug in the empeg and see if you get sound out of the speaker attached to it. If so, then it's on without a remote connection...
That most likely points to a broken amp turn on circuitry inside the amp...

/Michael

I'll have to wait until the car is charged to test it, but if that were the case, would it work to install a relay into the power lead and have that relay be operated by the turn-on lead? Or is the current in the turn-on lead not enough?

Well, the internal operation between the power lead and the remote turn on is in effect the same as a relay (small current controls larger...)
So if the fault is in the amp, and it stays always on, a relay on the +12V line, controlled by the remote turn on wire should work fine - just get a relay capable of handling the current the amp demands. Normal automotive relays are typically capable of 30A, though I've seen 20A and 40A as well.

You might want to connect the other (functional) amps remote turn on terminal to the switched terminal of the relay, so that the relay is the only thing powered by the remote turn on lead. If the relay doesn't come with a diode across the coil, consider installing one (1N400x diode should be fine), or some other protection.

/Michael

Hey, thanks for your detailed replies! Great stuff! With my trusty little multimeter I now found out that there is an increasing voltage on the turn-on lead of the majestic amp. It goes from 0.5V to over 1V within abnout 1-2min. I guess that's the culprit. I've taken the majestic amp off for now and its turn-on lead is also disconnected. Now I don't get any thump anymore, so I guess that's fixed now. Is there a permanent solution to the problem other than exchanging/repairing the majestic amp? Any ideas for stop-gaps?

It goes from 0.5V to over 1V within abnout 1-2min.

In what situation is that? With or without the remote connected? Both?
Sounds like you have something leaking power somewhere in the amp - maybe a failing cap - but the symptoms are weird...

Workaround: hmmm... I'd try running both the BAT+ and remote terminal off a relay controlled by the real remote wire (gives positive control of the remote terminal as well) if you can find a relay that can handle the current. You might get thumps - haven't ever wired an amp that way... and different amps act differently when it comes to thumping anyway.

Any warranty left on the amp?

/Michael

In what situation is that? With or without the remote connected? Both?

The amps are in really tight spots, so I could only test it with the remote wire out of the memphis amp, i.e. only connected to the empeg-remote.

Workaround: hmmm... I'd try running both the BAT+ and remote terminal off a relay controlled by the real remote wire (gives positive control of the remote terminal as well) if you can find a relay that can handle the current.

Sounds like a possibility. I'll probably try that.

You might get thumps - haven't ever wired an amp that way... and different amps act differently when it comes to thumping anyway.

Shouldn't be a major deal, since that amp only powers the small, mid-high frequency speakers anyway. Bigger deal will be to get to all the wires and get good connectivity, the way everything is installed now LOL

Any warranty left on the amp?

Bought it used off Ebay...
Thanks for your help!

Hmm, maybe my battery is still not fully charged, but my empeg blanks the screen and comes back up with the battery icon every time I break (the interior lights and headlights dim when I do that, too). The voltmeter also shows a dip of about 1V (to about 12.5V) with a negative spike going a little further down. If it persists after I verified full battery charge, do I have to change the permanent power source to a direct connection from the battery (oem harness for now), or is that a problem of the switched power supply? (I've read the FAQ)

The ignition wire is only used for signaling to the empeg (much like the remote wire to the amp), power is drawn on the permanent line (at least for the MkIIa, the MkII, IIRC could pull power from the ignition wire as well...)

Does it dim whenever you let the RPMs drop, even if you're not brakeing?
If no - look at ground points. The current through/from the brake light might be raising the voltage at a [bad/corroded] ground point so that things get confused (charging regulator etc) Any similar effect if you turn on/off other heavy consumers like fan or rear de-mister?

If yes; sounds like your battery is far from full and/or your alternator is struggling...

I'd check the battery further - being drained completely is bad for starter batteries, especially if they're a couple of years old.

Measure the density of the acid in each cell; it may not show full charge yet (1.28 - 1.30 g/cm^3) but should at least be consistent across all 6 cells. If one cell is significantly different you battery may be broken. Take it to a shop for a load test (draw heavy current from it while monitoring voltage - you should be able to draw the CCA rated current for about 10 seconds without the voltage dipping below 9V (if the battery otherwise is reasonably charged). If it does dip, look down into the "odd" cell (glasses recommended!) - odds are good that you'll see it bubbling/boiling (a lot more than the others) - replace battery.

Also check you alternator: should at least give a bit more voltage than pure battery voltage when car is idling; increase RPMs to about 2000, voltage across battery should rise to at least 13.8V, but not over 14.4V. If not, most likely your charging regulator needs replacement. On most modern alternators it is combined in a unit with the graphite brushes (the reg might be OK, but the brushes worn out - should give low voltages)

/Michael

Cool stuff in that reply! Thanks a lot, I'll test it out tonight!

Does it dim whenever you let the RPMs drop, even if you're not brakeing?

Only when I break, switch on the fan, blinker, lights, etc.

If no - look at ground points. The current through/from the brake light might be raising the voltage at a [bad/corroded] ground point so that things get confused (charging regulator etc)

Any ground points in the involved circuits or only those close to the alternator?

Any similar effect if you turn on/off other heavy consumers like fan or rear de-mister?

Yes! The amount of the drop varies, but I get it basically in all electrical consumers. With the blinker for example the effect is so small, I can only see it if the rpms are at idle. I really think it's because the battery is not full, yet. I'll check all that again tonight. It read 12V when I left the car last night. I'll see what happens now.
The battery is a Westco dry battery, only a few months old. I'm not quite sure if I should trickle-charge it or not. I usually tend to leave it to the alternator and only charge it with a charger if it is absolutely necessary.

increase RPMs to about 2000, voltage across battery should rise to at least 13.8V, but not over 14.4V.

It shows just under 14V on the highway (3-4k rpm).
If the problem persists even with a full battery, I'll have it checked out.
Thanks again for your help!

A dry cell battery in a car? Are you sure about this? These usually can't deliver the cranking current needed the way a wet lead/acid can. Are you sure that your battery is not meant to be a wet battery that has not received an acid solution?

This is an excellent piece and should go into the FAQ as a good diagnostic for battery state. Tony?

Rob: A dry cell battery in a car?

Bjoern: The battery is a Westco dry battery

Could it be a battery patterned after the Optima line of Gel-Cell batteries? These batteries are not of the normal "lead plates immersed in liquid sulphuric acid" construction, but have spiral-wound plates sealed in an acid gel.

The "Red Top" model in particular is known for being able to produce phenomenal current flow, both on output and recharge. In fact, this battery has revolutionized my snow plowing. The electric lift on the snow plow pulls a huge amount of current, and even though I have a 200 ampere alternator, a conventional battery cannot absorb electricity anywhere near as quickly as it can discharge it. So with a conventional battery I am limited to about two hours of plowing before I run out of juice. The Red Top, even though it has only half the capacity, will let me plow indefinitely because it recharges so quickly.

tanstaafl.

Rob: A dry cell battery in a car?

Bjoern: The battery is a Westco dry battery

Could it be a battery patterned after the Optima line of Gel-Cell batteries?

Another alternative is that it's a sealed acid cell battery. If so, then try peeling of any stickers on top - frequently you can find removeable lids underneath, so that you can get to the acid and measure density / check for bubbles under load.

/Michael

This is an excellent piece and should go into the FAQ

The benefit of 2.5 years working in Gothenburgs largest battery store...

/Michael

OEM Miata batteries are absorption glass mat.. Here's the WestCo replacement for it. Acid is suspended and immobilized in a fiberglass mesh between the plates. Small, light, lasts much longer than normal batteries, and they're safe, but they don't hold a hell of a lot of power. Since it's in the trunk, you don't want the acid of a normal battery leaking all over your stuff... and when a urban assault vehicle rear-ends you and crushes it, free acid flying everywhere or exploding on you wouldn't be good.

They require special treatment for charging, especially from a dead state.. low current (<= 1A) for long periods of time (18-24hrs); if you blast it with 20A like it's a regular battery you'll destroy it.

V99 is dead on it. I called it dry, because I remembered there was no acid floating around and no holes to peep through

The battery recovered over night, cranked fine and the empeg didn't blank out when I breaked.
However, on the way back, headlights on, after a few miles it started happening again: every break, empeg blanks out. Interestingly, it didn't do that for the first few miles, only as I got close to home. Is my for now single 300W amp drawing too much current together with the headlights? What if I switch the brights on? How about if I upgrade to overwattage bulbs? Do I need a bigger alternator? Bigger battery? Or do I just have to wait a few days until the battery has fully recovered from the drain?

300W isn't very much; fan + rear de-mister would probably draw around that...

How many amperes can the alternator deliver, max?

To me it sounds as is the alternator isn't delivering; once started the alternator should provide all the current you need, as well as charge the battery. Did you have the battery on a charger overnight?

What are the voltages across the battery 1) at rest (car off) 2) car idling and 3) car at typical running RPMs?

/Michael

This is an excellent piece and should go into the FAQ as a good diagnostic for battery state. Tony?

It sounds more like something for the CarTalk FAQ rather than the empeg FAQ.

300W isn't very much; fan + rear de-mister would probably draw around that...

I thought so, too.

How many amperes can the alternator deliver, max?

60, on paper. I'll have to check if mine still can do that.

To me it sounds as is the alternator isn't delivering; once started the alternator should provide all the current you need, as well as charge the battery. Did you have the battery on a charger overnight?

No, I figured I'd wait until the next morning, as I have experienced batteries to recover a little over night.

What are the voltages across the battery 1) at rest (car off) 2) car idling and 3) car at typical running RPMs?

The voltmeter I have installed (factory harness) says 1) 11.5V (ign. on), 2) and 3) are just under 14V, but drop about 1.5-2V with empeg and headlights.
I'm going to keep monitoring the behavior and measure accross terminals for a few days. I still think some more driving will restore the basically brand new battery in a few days and this weird behavior will subside. If it doesn't, I'll measure the max amps the alternator can deliver and replace it, if I have to.
Thanks for all your help, guys! Keep the suggestions coming!

OK, latest results: the voltmeter in the dash shows 13.8V if the engine is running and no electrical consumers. If I switch on headlights and empeg/amp it goes to under 12V idling and back to 13.8V when the rpms go up. With fan at full, headlights and empeg/amp on loud it shows under 12V, even at freeway rpms (3-4k). Do you think that if that behavior continues, I should have the alternator checked out or should I rather trickle charge the battery? Or both? With the engine off, the voltmeter showed just over 12V when I left the car last night.

It sounds like to me you do have a bad alternator, the voltage should not drop to 12V especialy on the road. It sounds like it's somthing to do with the regulator in the alternator, I would have it checked.

it goes to under 12V idling and back to 13.8V when the rpms go up.

It could be something as embarassingly simple as a loose alternator belt.

tanstaaafl.

It could be something as embarassingly simple as a loose alternator belt.

Possible. Given the way the Miata belts are tightened, I doubt it, though. I'll check it to make sure, however. It is getting slightly better each day, so I think battery charge playes quite a big role in this.

But back to the original problem (the Majestic amp generating a voltage on the remote turn-on lead): Is it possible that a remote turn-on lead routed right next to the constant power wire could induce the increasing voltage? Or is the amp necessarily faulty? The amp does produce some noise (low level hum), but it's a cheap one and I never expected it to be perfect.

Hmmm,

came to think of the reports of problematic electrical antennas that wouldn't go down efter the signal was removed...

Try wiring a 1kOhm, or so, resistor between the amp remote terminal and ground.
Might bleed off the buildup...

/Michael

Cool idea! I have the resistor right here next to me as I type this and am going to try it this weekend! Thanks!

Aha, I knew this sounded familiar

Aha, I knew this sounded familiar

Sure I figured I had to ask the experts on both sides of the harness

Try wiring a 1kOhm, or so, resistor between the amp remote terminal and ground.
Might bleed off the buildup...

I put the resistor in there and it does bleed the buildup nicely. However, I measure quite some current going through the resistor. Problem is, while my multimeter works just fine for resistance and voltage, it gives me weird readings for current! If I set it to 10A it reads 0.57. If I set it to 2000mA it says 57, if I set it to 20mA it says 5.7???? That doesn"t make any sense to me at all. There is a big difference between 570mA and 5.7. The multimeter works just dandy in all other aspects, but that just throws me off. How much current is actually going throug the resistor "down the drain"? According to Ohm's law (I=U/R=12V/1000ohm) I shouldn't get more than 12mA, so should I assume it's only 5.7mA (which would be perfect)?

While you can measure voltage and resistance between two pins, current has to be measured through something. What you need to do is put the meter in series with the circuit you want to measure, not in parallel.

What you are measuring right now is the current through your multimeter (and yes, that varies depending on range, as the resistance is different on different ranges) instead of through your circuit!