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helton333
07-09-2009, 09:01 AM
if you have a ground from an amp going to a freestanding battery (i.e., isn't connected to the engine block ground) - do you really have a good ground?

mpabreo
07-09-2009, 09:45 AM
yes.......

helton333
07-09-2009, 09:51 AM
Thanks - electronics are a tad confusing -

JimN
07-09-2009, 10:18 AM
if you have a ground from an amp going to a freestanding battery (i.e., isn't connected to the engine block ground) - do you really have a good ground?

You may have a good ground to that battery but it can't be assumed (could be loose or dirty).

Let's assume it's clean and tight- That accounts for the current supplied by that battery but how is that battery charged? Where is the head unit and the rest of the stereo connected? If it's connected to the main battery and the second battery is grounded to the block instead of directly to the first battery or to some other common point, any resistance between the head unit's ground and second battery's negative will cause noise. If the second battery isn't grounded to the rest of the electrical system, it'll never charge.

The simple answer is that you may have a good ground to that battery but the rest of the system may be completely isolated, which isn't good.

If you add a battery to a stock electrical system, the added load may overtax the alternator and that will eventually lead to its failure. If you upgrade the alternator, the charging lead will need to be larger too, because what came with the boat was for that capacity, not more. The charging lead from the alternator would go to one battery and ideally, the distance from that point to both batteries will be the same. This is easy to accomplish with a distribution block, if you want to be really picky about how it's done. In most situations, some difference in length is OK as long as the accessories don't draw an extreme amount of current.

If you don't isolate the batteries from each other, the positive and negative terminals need to be connected with a heavy cable so no resistance will be present. The ground cable to the motor is only for the starter and any electronics on it- it has nothing to do with the stereo system, other than making sure the motor and all other electronics are effectively grounded to one electrical point. As long as there's no resistance with the desired load between two ground points, they're electrically the same.

helton333
07-09-2009, 10:51 AM
I have 2 blue tops - not connected (tried that - alternator wouldn't charge both and I wasn't ready to start changing that out on a 20 year old prostar) - the head unit and amp, both go to the same battery now - we only use the boat an hour or so at a time as it is at the lake house and we come and go often during the day - I may add another battery but at this point, we have tried everything but still have the tower speakers (not the in boat polks) cutting out at slightly higher than running speed sound - it certainly doesn't take a full blow turn up to produce the cutting out - we replaced amp, head unit, still have the issue - and both speaker sets do it simultaneously, which leads to something other than the speakers themselves. So I am looking at a ground issue. The starter battery is of course grounded to the engine block, but not the battery the stereo gear is running off.

denverd1
07-09-2009, 10:58 AM
I'd ground both to the engine block. I have separate batteries for stereo system as well. Running 3 amps w/ 4 batteries - all grounded to the block. 2 are stereo, 2 are starting. No issues in 4 years.

JimN
07-09-2009, 11:44 AM
I have 2 blue tops - not connected (tried that - alternator wouldn't charge both and I wasn't ready to start changing that out on a 20 year old prostar) - the head unit and amp, both go to the same battery now - we only use the boat an hour or so at a time as it is at the lake house and we come and go often during the day - I may add another battery but at this point, we have tried everything but still have the tower speakers (not the in boat polks) cutting out at slightly higher than running speed sound - it certainly doesn't take a full blow turn up to produce the cutting out - we replaced amp, head unit, still have the issue - and both speaker sets do it simultaneously, which leads to something other than the speakers themselves. So I am looking at a ground issue. The starter battery is of course grounded to the engine block, but not the battery the stereo gear is running off.

Measure the voltage at that battery when the stereo cuts out- it's going to be low. If that battery isn't grounded to the motor, it can't charge. Also, if the head unit is connected to the primary battery and the amp isn't, the second battery is trying to ground through the audio cables and the turn on lead. Run a ground from the secondary battery and measure from that battery's ground post to the one on the primary battery- if it's less than .1 Ohms, you're OK. If it's higher, you'll probably have some noise because of a ground loop. You should set the input sensitivity controls on the amp according to the manual, too. That makes a big difference. The amp is cutting off because it's overheating, due to low voltage.

Again, if you do connect the second battery to the block and you try to charge that, the primary battery and run the rest of the accessories, your alternator won't last long.

Also, if the secondary battery is badly discharged, use a charger- don't start the motor and try to charge it that way. It's really hard on an alternator.

bainez23
07-09-2009, 11:48 AM
yes or the amp will not work

JimN
07-09-2009, 11:54 AM
I have 2 blue tops - not connected (tried that - alternator wouldn't charge both and I wasn't ready to start changing that out on a 20 year old prostar) - the head unit and amp, both go to the same battery now - we only use the boat an hour or so at a time as it is at the lake house and we come and go often during the day - I may add another battery but at this point, we have tried everything but still have the tower speakers (not the in boat polks) cutting out at slightly higher than running speed sound - it certainly doesn't take a full blow turn up to produce the cutting out - we replaced amp, head unit, still have the issue - and both speaker sets do it simultaneously, which leads to something other than the speakers themselves. So I am looking at a ground issue. The starter battery is of course grounded to the engine block, but not the battery the stereo gear is running off.

Why don't you want to replace the alternator? Either you want it to work properly, or you don't. You already threw more money at it by replacing the amp and head unit than an alternator would have cost and since you didn't wire the second battery to the block, the second battery isn't doing its job, either. Adding a third battery will only compound the problem and could damage the head unit because the batteries will try to find a better ground path, which will only be found through the wires to the head unit.

Not to rub salt into the wound but how much do you figure was saved by not taking it to a shop for installation?

Edited to add that if it was installed by someone else, this definitely qualifies as a rework, at no cost to you.

btriantos
07-09-2009, 12:04 PM
I'd ground both to the engine block. I have separate batteries for stereo system as well. Running 3 amps w/ 4 batteries - all grounded to the block. 2 are stereo, 2 are starting. No issues in 4 years.

How do you have this wires, and do you have an upgraded Alternator that adequately charges them? I have four amps hooked up on my set up with the stock batteries. I have an inline charger/conditioner for both batts currently, and I'm hoping it's enough. I do not run the stereo too long with the engine off. 45-60 mins tops, and it's not near max volume.

TallRedRider
07-09-2009, 01:15 PM
Not grounding the battery to the engine sounds like an absolutely perfect recipe for this type of electrical gremlin to come into your system.

Maybe the battery still functions, but you have all sorts of issues that come up. I would do the ground cable first.

Now what are we worried about your alternator for? It can't charge 2 batteries? I understand larger systems having issues, (like 3-6 batteries) but I suspsect without running the batteries completely dead, the alternator should be able to keep up with a 2 battery load.

To restate what JimN is saying, now you are holding out on a $15 ground cable and replacing hundreds of dollars elsewhere?

helton333
07-09-2009, 01:16 PM
we didn't take it in because it is something minor - we had wash come over the windshield which had affected the head unit anyway - the local audio store was sure it was the amp. I guess my question is. Should a second battery, not connected to the started battery, be grounded to the engine block as well? ALL audio - head unit and amp, go off a second battery, not connected to the starting battery, thus not connected to the block.

helton333
07-09-2009, 01:18 PM
no I have the cable to install - it was $5. Do I just run that from the negative battery post to the engine block, or do I need to put a bus in there somewhere with the amp grounds going to it? I only have 2 grounds going to the second battery - amp and head unit.

JimN
07-09-2009, 02:06 PM
we didn't take it in because it is something minor - we had wash come over the windshield which had affected the head unit anyway - the local audio store was sure it was the amp. I guess my question is. Should a second battery, not connected to the started battery, be grounded to the engine block as well? ALL audio - head unit and amp, go off a second battery, not connected to the starting battery, thus not connected to the block.

The charging circuit isn't complete if the second battery isn't connected to the block. If the negative post of the second battery is connected to the negative post of the main battery, it is. Think of what a circuit is- it starts somewhere, goes to something and needs to go back in order to be complete. If it doesn't, it's not a completed circuit. The answer has been posted several times now, with explanations.

You can ground it to the block but If the second battery is next to the main one, just run a heavy cable with a fuse to the main battery, both positive and negative. If the second battery is farther from the main one, run a pair of cables to the main battery, with a 100A breaker on the positive lead. The breaker should be no more than 12" from the main battery. To be completely safe, another breaker should be located the same distance from the second battery, for worst case scenarios. The negative cable doesn't need a breaker. Do not run power cables parallel to other wiring, especially control wires for head units, an ECM or audio cables. Any time power cabling crosses other wires, it should be at a right angle, to minimize the chance pf noise being picked up by the other wires.

If the audio store knows what they're doing, they should have tested the amp separately for operation, output and current draw. If they just looked at it and tried to sell you a new amp, that's all they're concerned with- selling, not service.

helton333
07-09-2009, 04:01 PM
thanks - will do

helton333
07-09-2009, 04:19 PM
if I hook the connection back up between the 2 batteries, (I have a Borg Werner cut off between - key hot) - is the fact that they are not the same battery a big deal?

JimN
07-09-2009, 05:19 PM
if I hook the connection back up between the 2 batteries, (I have a Borg Werner cut off between - key hot) - is the fact that they are not the same battery a big deal?

Yes and no. If the alternator is able to operate with an extreme load (an old and/or very discharged battery), the one that presents more of a load will drag the charging voltage down until that battery comes back up to a more normal level of charge. The problem with this scenario is that the alternator/regulator will run hot and this leads to failure, especially when the alternator has many years on it. The brushes are probably the easiest thing to replace (if they don't go flying out, like they did the first time I took one apart) but the bearings, windings, regulator/rectifier and contacts all take a beating when it's abused. If you really want more output from the stereo and better dependability, assuming the alternator knows about Murphy's Law too, is to upgrade the alternator and charging lead. The amps will last longer because they won't overheat due to low voltage, your head unit won't suddenly fry because the amps were making up for bad grounding through it and you won't be stranded at the worst possible time. For less than $150, you can get one that's good for about 100 Amps and that should work for what it sounds like you want to do.

This link has tons of information about how to properly wire the power and grounds, as well as working with speaker crossovers, speaker loads, etc:

http://www.the12volt.com/ohm/ohmslaw.asp