Alternator Upgrade Options

Alibuma

Alibuma

New Member
Jun 24, 2009
140
Hudson, WI
Boat Info
250 Sundancer, 1973
Glastron GT-140
Engines
350 Merc
Hi Everyone,

Please forgive me if this belongs in the Engines thread but I thought it might better here. I am going to buy a spare alternator to keep on the boat but am debating on what to do.

I have a 250DA w/ a 350 Merc. We spend most of our time idling up and down the river (max 800rpm). Maybe once or twice a weekend we'll get up on plane and cruise for 10 to 15 minutes. At night we have shore power or the boat goes back on the trailer and gets plugged-in to the house. We have one house battery and one starting battery currently running through a Perko 3-way switch. At the end of a day draining the hosue battery, I would like to have enough alternator capacity on the ride back to the dock (1 hr put-put) to run the onboard electronics (factory + stero + spotlight on occasion) and still recharge the house battery. Future additions may include an inverter and a TV, but I dont have those now and am not weighing them heavily in this decision.

I was thinking of upgrading the 65a factory alternator and keep it for my spare. In its place, I was considering putting in a 100a with a smaller pulley (to obtain adequate chargine power at lower rpms), or a 140a. There's really not much difference in price but I dont know if 140a is overkill.

Also, I found several marine alternators on eBay. Has anyone had good or bad experiences with them?
 
Based on what I was told by my mechanic if you go over 70AMP alternator you will need two pullies on the alternator. At 800RPM it is probably not charging very much. I find my batteries stay low until I get up to 1800RPM.
 
Are the fan belts tight? Have you tested the batterys correctly??-Charge then a draw test? Remember it all starts with the batterys. I have a 89 340Da and never had this issue. I buy interstate RV-Boat 27 batterys. try the test first. Also check the output of the alternaters Amps and volts.

Rick
 
Northern - what size alternator are you using

Flarepoman - I was asking for advice, not troubleshooting a problem, but thank you for replying.

Anyone else? Maybe I should have posted this in the classic's thread. There seems to be more hands-on owners in that thread. If anyone has any advice, I would appreciate it.
 
I'm not sure that upping the alternator charging capacity is going to help you. At idle - low speeds, no alternator is doing much charging. Going to a smaller pulley is not a long term solution as you would have to basically double the RPM at idle speed to spin the alternator fast enough to start doing some good. That's ok at low speeds, but what happens when you do drive the boat at planing speeds? The smaller pulley is still making it go 2x faster.

Added to that, it also sounds like you are pretty regularly stressing the batteries running them down during the day and charging them up on the trailer.

I'm pretty sure you don't have a 'house' battery. A single engine setup with a 3 position switch is usually two starter batteries that are wired in parallel with an isolation switch between them. You may use Position 1 for 'engine' and Position 2 for 'House', but they are both working together. Since both can only charge when the switch is set to 'Both', you have to run the engine on the both setting. By using one as a dedicated 'house' battery that regularly is discharged it will begin to develop a different charging pattern than the other battery in that one battery will charge faster than the other. Once the batteries begin to develop different charging patterns the strongest battery (the one that reaches charge first) will cause the charging circuit to stop once it is at full charge. That means your house battery is chronically getting undercharged.

A better solution might be to go to two 'dual purpose' batteries that can take more charge to discharge cycles than starting batteries. Also alternate which battery is the house battery (I use even dates for 2 and odd dates for 1) to keep them in the same state of health. And finally try and get a little more high speed running. I know it can be hard, we have a 45 minute no wake run down river to the ocean so I have been in the same position as you are in.

Henry
 
Henry, thank you for the insight. I may be using the term "house battery" loosely. I think that based on what you are telling me I have been charging my battery incorrectly. I have been switching the switch to #2 to charge what I call my house battery. Now that you've given me more to think about, the wire from my alternator only goes to #1. Therefore I have to have the switch on BOTH to charge both... interesting.

So in this case, do you think the Blue Sea Automatic Charging Relay would help me out? I do hate remembering to switch between batteries and it sounds like my second battery may never get a good charge the way it's wired now.

Also, based on my situation, would you recommend purchasing another 65a alternator for my spare? Has anyone had any luck (good or bad) with the ones on ebay for about $75?

Thanks!
 
Yes, battery switch 1 and 2 are mutually exclusive when it comes to discharge and charging. When the boat is moving the switch should be set to both to ensure both batteries are being charged. Down side is that both batteries have to be identical.

For starters you should think about testing the batteries. If one is cooked, you are going to continue having problems. If that is the case, you have to replace both with the current set up.

I have looked at the Blue Sea ACR, unfortunately in not enough detail to know exactly what would have to be changed. One thing that would change (besides making sure the switch is set to both) is that you could place a seriously large starter battery in position 1 for engine operation, and then have one (or more in parallel) deep discharge batteries for house functions. The ACR (and I belive another bit of hardware) will allow two disparate battery types to coexist, and be properly charged.

Before you spend a lot of cash on new hardware do the battery test. One battery being different from the other will mean that things have not been working the way they should. If they are dodgy, then think about batteries and possibly an ACR solution.

Henry
 
My starting battery is a standard starting battery. The other is a larger deep cycle. Both were brand new last year. I dont want to replace the alternator for any reason other than having a spare to keep on the boat. Same with the starter. There's nothing wrong with either, I just want spares. Thank you for your replies and the insight.
 
Alibuma said:
My starting battery is a standard starting battery. The other is a larger deep cycle. Both were brand new last year. I dont want to replace the alternator for any reason other than having a spare to keep on the boat. Same with the starter. There's nothing wrong with either, I just want spares. Thank you for your replies and the insight.
Click to expand...

There you go. The ACR is your upgrade as it will allow two dissimilar batteries to be kept up to charge in the most efficient manner.

Henry
 
Awesome! Thank you. I love user reviews and find them much more useful than the product literature. Did you install the ACR in the engine room? Does it appear to be pretty well sealed from moisture?
 
Yep I installed it right where the old battery isolator was installed since the port and house batteries are. It is all sealed in the hard electronics plastic except for the terminals and should not have a problem with moisture.
 
Alibuma
I had 55 AMP alternators when I got the boat then had 70 AMP ones installed. The mechanic said if I was to go to any thing bigger (next size was 100AMP) I would need double belts. Original alternators worked fine but I have 4 Group 27 beep cycle batteries for start and house plus ten 6 volt golf cart I can switch from generator charging to alternator charging. I run a 2600 watt inverter. We tend to use oven when running and the alternators keep the house batteries up.
 
Northern, thats a heck of alot of batteries! WOW! If you're charging all of those with 70a alternators, then I should be just fine! I think I'm going to add the Blue Sea ACR this spring and buy a standard sized alternator for a spare. That seems like the most logical approach after reading the responses.
 
Alibuma
We also have an 8KW generator we run for 2 hours a day it has an inverter that puts out 140 AMPS for the house batteries. The start batteries have a 60 AMP charger. The two 70 AMP alternators will in a 10 hour run fully charge all batteries. All depends what you want to use your batteries for. We have an ice maker we leave on all the time. It draws lots of power.
 
The Blue Sea ACR's are one of the best products they have in their lineup. I have installed about 150 in the last two years, and have yet to have a issue with any one of them. Installation is straight forward, and the come with a almost lifetime warranty.

As for your alternator, if you find yourself at low speeds, and the alternator won't stay excited (steady charging), you might want to have it brought to a automotive electric shop and have a smaller pulley put on. I use this a lot on commercial boats that idle all day pulling fishing nets.
 
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