Guys,

Data dump..... During my 496 rebuild, we retained the OEM alternator. I even took it to a local alternator/starter shop, had it tested and was told it was actually putting out more than it was rated for (don't remember the number). Not so much that the regulator would be bad, just a bit more than rated. I also replaced the entire fuel delivery system, from tank to intake, including a massive fuel pump that is undoubtedly more than I need. It is the pump that Weldon made for the Merc 1075 and 1200s. Like I said, more than I needed, but it came cheap, and I knew it wouldn't fall short. Over the course of the project, I also added an automatic charging relay, so both batteries would be charging while the engine is running but separated otherwise (I have it rigged as Batt#1 and batt#2, not start/house). And lastly, I added a second bilge blower. You know... Just in case. After all is said and done, engine back in the boat and running, I am showing significantly reduced voltage at the gage. With the engine running and the blowers on, the gauge shows ~10.5v. I've checked at the batteries, however, and they both meter at ~12.5. I haven't checked at the batteries, but with the blowers off, the gauge shows a little over 12v, so I'd assume at the batteries would likely meter at well over 13v. So far, we've put several hours on the boat (15+) since getting it back in the water, and the starter has never faltered even a little bit, even after several hours of running the stereo while anchored, but I can hear the fuel pump sag while the engine is cranking over (I've never thought to glance down and see if pressure drops, but I have to assume it does). I keep both batteries on charge when it's on the trailer, but they never show more than ~12.8v after a day's running; typically ~12.3v. I have a 29D series battery, that the Holley HP is connected directly to, as batt#1, and a 27D series battery as batt#2, which is the one I have been starting on, just to make sure to hopefully never have a low voltage situation with the Holley (that's when it will dump the tune, as I'm told). For context, I don't really have any pre-failure data on the charging system, other than we never had an issue.

So, what's going on? Am I swelling on something that isn't an issue? My biggest fear is a low voltage condition at startup and the ECM dump the tune. I've got the global file on a thumb drive, and on our laptop, but I don't carry it with us unless the tuner is going to be doing some tweaking. The tech at Weldon told me, if memory serves right, that the pump draws ~18A at 50psi, and the blowers draw 2.5a each. My presumption is that, between charging both batteries simultaneously, the massive fuel pump and the two bilge blowers, the OEM alternator is just falling a bit short. The CFO has already expressed her displeasure with the whine of the fuel pump, so I'm probably going to be replacing it over the winter with a turbine style pump that will draw less current (open to suggestions), but I'm inclined to keep the dual bilge blowers. Should I be looking for a higher output alternator? If so, what are my options that will drop right in?

Thanks. Brad.

If you checked the voltage at the batteries with an actual voltmeter and you have around 13 volts with the engine running and the blowers on then you are probably ok. I would check the voltage at the gauge with a voltmeter and see what you get. If it is 12 volts and the gauge is only showing 10 then you know that the gauge is the problem. If you get less than 12 volts at the gauge connections then you have a wiring issue.

I'm going to convert mine to Holley ECM's, is this tune dumping a thing? I have not heard of that but that could royally suck any idea of how common it is?

I have two of the Weldon's like you do and they are not particularly noisy. I also have two of the marine A1000 Aeromotive pumps in my system. Do not use those they suck and will fail. I've replaced both of them already and this last one that failed, I used the different Weldon version (similar to the Aeromotives) that is also much quieter and will not fail like those steamy piles of s%&*.

Dave,

Good to know on Aeromotive. That’s actually what I was looking to get when the Weldon kinda dropped in my lap.

The Weldon is pretty loud. The tuner tells me that’s just what gear pumps sound like. It could be because I’ve got it hard mounted to the transom and it’s using the entire hull as a soundboard. I’ve considered mounting it with rubber grommets. But, if I’m gonna replace it for other reasons, I won’t bother.

My tuner tells me the only times he’s seen a Holley ECM dump the tune is if you let the batteries get really low and try to start the engine. Essentially an extreme low voltage condition. Not sure what that number is, though. And this is the core of my concern with my battery/charge situation.

Thanks. Brad.

BillK,

I’m getting ~12.5 volts at the batteries, blowers running which I’m guessing is just barely enough to keep them from discharging while running.

I will have to check under the dash, but I’m not sure I’m going to be able to get a running value until after the season is over. I do need the change the oil again. Maybe I’ll take that opportunity.

i can tell you the volt meter jumps significantly when I switch the blowers off. It’s hard to imagine, with all the other things that draw significantly more, that those two 2.5A blowers are having that much impact on their own. Leads me to believe it’s on the low threshold otherwise.

Thanks. Brad.

Do you run your blowers continuously?

Padraig

Padraig,

No. Not intentionally, anyway. I have been known to forget to turn them off.

My concern is being that close to maxing out the output of the alternator that two 2.5A motors are enough to slowly discharge the batteries while running.

Thanks. Brad.

Boat wiring to helm can cause odd measurements at the dash. There's likely one hot wire that powers everything on the dash.. If accessories (like blowers/pumps/lights/nav equip) are powered from the dash wiring, that puts a load on the main hot wire pulling the voltage down to the dash mounted volt gauge. The more stuff you power from the dash, the more the voltage drop you get on the main hot wire..

Some of this can be addressed by using relays to power high current items. That way the dash power only has to engage the relay and not actually power the accessory.

In some cases, you can run a larger wire from the batt (or batt switch) to the dash and help prevent large voltage drops. Same for the dash main ground wire since there's not return path in the chassis like most cars have.

I would check voltage at the batt with eng running and all accessories that you would normally run powered-up. If it's low there, you may have more power going out than coming in. Also remember that most alternators don't produce full output at idle.

On one of my prev boats, I couldn't get the spotlight to power up from the cig lighter outlet even though I measured 12V with my handheld meter. Discovered someone had made some wiring mods before I got the boat. Cig lighter was being powered from the clock which was fed by a 22ga wire! Ran dedicated (and fused) 10ga wires (hot and gnd) from the batt to the cig lighter outlet. Spotlight worked great and dash lights didn't dim down nearly as much.

Fuel Pump hard mounted to the hull is likely your megaphone issue.

Sounds to me like you have the perfect setup. CFO is complaining about the fuel pump...and not the thru-hull exhaust....

Having a voltmeter directly connected to the batts is the way to go. Even digital would be goo. One for each batt.

Your blowers are not taking up a lot of current...no different than running headlights...heater fan, wipers etc. What isnthe Holley drawing?

18A fuel pump​
5A Blowers
?? HOLLEY

Not a lot of draw.

The thing to do is test the current output of the Alt while in use. Inductive meter. Otherwise, you're just guessing.

I may have missed it, but have you checked voltage directly at the alternator while running?