Grounding both batteries off the same lead

[Baltimore Sailor]

I have a marine starting battery on the 1 post of the battery switch and a marine deep-cycle battery on the 2 post. The run from the battery switch to the starter and ground on the engine is about four feet of #4 AGW wire for both the positive and ground leads. I have one ground lead that comes from an engine bolt to the 2 battery, and a short #4 lead from the 2 to the 1 battery.

The problem is that the 1 (starting) battery doesn't seem to put the juice through to start the engine. If I put the switch on Both or 2 I have no problem, but 1 just can't cut it. The battery is only a year old, and I just had Sears diagnose it and they say it's on a full charge.

I did replace the short lead from the starting to the deep cycle (1 to 2) with a new cable, and I was able to barely get the engine to start.

Assuming the battery is in good shape as Sears says, what else could be dropping the amps across the circuit to start the engine? Is going through the 2 battery possibly the reason?

[Dave O]

Have you actually checked the battery yourself? I know that sounds a bit basic but I prefer not to rely upon a third party for that. I generally check the charge with a voltmeter about 1 x a month just to make sure before I head out.

I was caught 1 time last year on Lake Ontario with a dead # 1 battery. I got going on # 2, but had to replace both with new deep cycles and ever since I have been very cautious.

For more information you might like to check this out:

http://assets.fluke.com/appnotes/ele...r/B0270b_u.pdf.

Please note I work for a sister company of Fluke Electronics and I use their products so I am not unbiased about their volt meters, but I think the article is very helpful. Others might be able to comment about the content.

[SEMIJim]

Is going through the 2 battery possibly the reason?

You're not going "through" your #2 battery for anything--it's just the negative (ground) is jumpered from one battery to the other.

Can't be the negative connection at the #2 battery, or you'd have the same problem with each.

Could it be the positive (cable or connection) for the #1 battery? The switch?

Why don't you try swapping the batteries and see if the problem stays with the battery or with the location? That's what I'd do. If the problem stayed with the battery: You'd have your answer. If it stayed with the location, next I'd try swapping the #1 and #2 connections at the switch. If the problem still stayed with the location (which would now be on #2), I'd suspect the positive cable. If the problem stayed on #1, I'd suspect the switch.

Jim

[rigspelt]

For more information you might like to check this out:
http://assets.fluke.com/appnotes/ele...r/B0270b_u.pdf.

That's a keeper! Thanks.

[msauntry]

The main switch itself could be bad. If you switch the leads on the batteries and still have the problem with the new #2, its either in the wiring of the #2, or the switch is shot. Unless you see physical damage on the cables or severe corrosion, its probably the switch. Not much can go wrong on a cable...

[Baltimore Sailor]

It was the switch. I swapped the cables between batteries and the problem followed the cables. Then I figured I had to move the cables as well to determine whether it was the switch of the cable, so I did that as well. The problem stayed with the post on the switch, so I went over the Boater's World and picked up a new battery switch.

All my battery problems went away, and my temp gauge even quit reading max all the time before I started the engine. There must have been some short in that switch!

Now my only problem is that my voltmeter only reads 12.5v when charging while the engine is running. My ammeter never reads anything and it's a long run from the alternator to the ammeter to the BATT post on the key and back to the large terminal on the starter. How can I test the output of the alternator at the source rather than after that long run? Can I put a voltmeter right at the post on the alternator and check it there?

[jhwelch]

It sounds like your alternator is not working.

You should be able to measure the voltage at the output terminal.

And it's pretty easy to remove it and have it tested for free. I've
had the diodes go on mine when the battery was switched off
with the motor running (the old Motorola alternators are prone
to this happening to them). And I once had an internal wire
come loose.

-jonathan

[SEMIJim]

Concur with jonathan.

Jim

[Baltimore Sailor]

To measure at the output terminal of the alternator, I'd put the positive lead from the multimeter on the output and ground the negative wherever, right?

How would I know that I wasn't just seeing the 12.5v from the batteries if the alt just wasn't putting any juice out at all? 'Cause I have to have one of the batteries on line to run the alternator, else I will burn it out, correct?

[jhwelch]

Baltimore, you have the right idea how to see if your alternator is working.
Any voltage above 13.3 or so means that it is doing at least some work.

I used to always undercharge my batteries with the Motorola alternator
and the regulator that is mounted on the housing; I think they charged
around 13.4 or so. Now I charge at 14.4 and don't have to replace
my battery every 2 years, as it's getting properly charged by a
smart regulator.

-jonathan

[SEMIJim]

Now I charge at 14.4 and don't have to replace my battery every 2 years, as it's getting properly charged by a smart regulator.

Did you replace just the regulator, or alternator and all?

Jim

[jhwelch]

On my Motorola with the external bolt-on regulator I took that off,
had a wooden part made up to cover the exposed wiring, and
ran a bundled cable from my external regulator, which is mounted
on a bulkhead. I made up the connections so it's easy to reinstall
the original regulator or swap the alternator for my spare Mando
brand I got from MMI.

It's an easy process, I just had to install a SS bolt in the wooden part
to "bring out" a wire connection the old regulator connected to.

-jonathan

[msmith10]

Jonathan,
Where did you get the external regulator? Any preferences on brand, model #? Approx cost?

[jhwelch]

This product seems to have replaced the regulator I have; it has all
the features of mine, and then some, and the wiring harness is the same:

http://www.xantrex.com/web/id/107/p/docs/pt/7/product.asp

I don't know what current prices are; I paid over $100 at West Marine
for mine years ago. I use my boat a lot, so having a properly charged
battery was well worth the expense.

-jonathan

[rigspelt]

I used to always undercharge my batteries with the Motorola alternator and the regulator that is mounted on the housing; I think they charged around 13.4 or so. Now I charge at 14.4 and don't have to replace my battery every 2 years, as it's getting properly charged by a smart regulator.-jonathan

We bench-tested my original Motorola 30 amp alternator. It puts out about 30 amps at 13.2 volts. Will the new smart-charging external regulators boost voltage from that old alternator?