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Old 07-29-2015, 09:51 PM   #1
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Charging question

I have a portable generator that I run while underway to power a few things (an ice machine, a freezer and some power outlets to charge my phone among other things). Since the alternator is providing power to the batteries While underway I always unplug the charger from the main system because I was afraid that having two power sources to the batteries might not be a good idea (I plug the power supply from the generator to the AC input on the boat, just luke I would at the marina). Am I right or could I also have the charger ON to provide more juice to the batteries? The reason I ask is because the alternator doesn't provide enough juice to replenish the batteries. After two days without going to a marina to plug in, the batteries are approaching a critical level. I'm thinking that if the charger suplied additional juice on top of what the alternator is giving that I might have more autonomy. Or would it cause a conflict or an overload to the batteries? Don't want to risk busting the alternator or the generator. Thoughts?
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Old 07-29-2015, 10:17 PM   #2
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I'd want to have an alternator capable of powering all systems and at the same time charging the battery. What's your alternator's output versus your power requirements?
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Old 07-29-2015, 10:26 PM   #3
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I'd want to have an alternator capable of powering all systems and at the same time charging the battery. What's your alternator's output versus your power requirements?

Not sure but obviously not enough. But the thing is I only really need more power 2 weeks a year when I go on vacation. Trying to see if I can make up for it some other way. Not worth investing in a new and expensive alternator.
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Old 07-29-2015, 10:34 PM   #4
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I'd first try running the generator only when not underway. Maybe the portable generator isn't enough to power "household" power needs. Perhaps your batteries are worn out.
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Old 07-29-2015, 10:34 PM   #5
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I don't think you can harm anything. It all depends on the charging voltage profile for the alternator and the battery charger. When the batteries are low, both should charge and you should get more amps into the battery. At some point the unit providing the higher output will take over as the voltage comes up. What kind of regulation to you have on the alternators?
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Old 07-29-2015, 10:49 PM   #6
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I agree with Dave.
A couple more questions come to mind.
Is your battery charger a fairly new model with 3 or 4 charge stages?
If so, probably no problem at all - it should drop out around 14 volts into "Float" mode, and defer to your alternator.

My bigger concern is whether your Generator can handle the battery charger AC load in addition to your other loads, Ice machine, freezer, outlets, without overloading the Generator. Conflict with the alternator would be my least concern.
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Old 07-30-2015, 01:14 AM   #7
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The alternator should be providing enough to recharge the batteries, I`d be checking the alt and the batts.In fact it might be worth investing in a more powerful alternator.
I have had the alternators, solar, and battery charger (powered by genset) on at once, with no apparent issue.
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Old 07-30-2015, 05:55 AM   #8
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"It all depends on the charging voltage profile for the alternator and the battery charger. When the batteries are low, both should charge and you should get more amps into the battery."

When being charged the battery V rises .

Both the 120v charger and alt only charge by measuring the voltage and applying a charge to what they see.

With both on only one will charge .Same as with 2 alts , one will charge , the other will not.
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Old 07-30-2015, 08:04 AM   #9
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I agree with FF....you may get a bit of an extra charge, but not much as one charge source will be confused by the other. Won't hurt the alt or genset...just doesn't do much. You may not need to do an expensive alternator upgrade to amp up your charging: a better regulator may be all that's needed to make the existing alts work harder
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Old 07-30-2015, 09:20 AM   #10
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It isn't obvious to me if your need is to increase battery charging underway or to last longer on the hook without discharging the batteries too far.


Charging with both the engine's alternator and the generator powered shore power charger is no problem. The problem will be balancing the loads on the generator.

If you have the ubiquitous Honda EU2000 generator then its maximum continuous AC output is 13 amps. A typical shore power charger of 40 amps DC capacity can easily consume half of the generator's AC output. And I agree, both the alternator and the shore power charger won't significantly increase the battery charging rate.

The simplest and cheapest solution is to just run the generator on the hook to keep the batteries charged. Also if you have room, add batteries to carry you longer on the hook. Another solution is to change out your engine's alternator to a high output one with an external three step regulator. That change will significantly increase your battery's charging rate while you are underway.

You have to look at your on the hook DC demand, the size of your batteries, your on the hook charging capability, how many days on the hook before starting the propulsion engine to go somewhere else, to figure out the right solution.

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Old 07-30-2015, 09:24 AM   #11
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Multiple chargers will not interfere with each other. Both outputs are sloppy waveforms with peaks well above 12V. The voltage they provide to the battery will depend on the state of charge of the battery.
Depending on their design they may share the load. If your batteries are very low both will probably charge to max current for a while until voltage rises. Then one may reduce charge before the other. You don't care because your problem is very low batteries.


If you had an inverter charger that might be different.


I regularly leave my battery charger on when on the dock, or underway with the generator and engines running.
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Old 07-30-2015, 09:34 AM   #12
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How about installing a battery monitor? That will let you know exactly what is going into and out of the batteries.
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Old 07-30-2015, 10:03 AM   #13
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A voltmeter will give you a good idea.
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Old 07-30-2015, 10:12 AM   #14
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Or better, a clamp ammeter
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Old 07-30-2015, 08:22 PM   #15
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Lots of great input. I do have a Xantrex battery monitor, that's how I know the alternator gives less than what I consume while anchored and I have a deficit after each day. I did try to run the generator while underway today and it does provide a boost (or the 120 volt charger works better than the alternator). I have a 50amp alt but I never see more than 6-7 amps being provided to the batteries. Not sure if this is how it should be. When I ran the generator today it went up to 9-10. Not a huge difference but on the course of an entire crusing day it would make a difference. The generator works a lot harder though so I'm not sure I'll be doing that anyway. For me running the generator while on the hook is out of the question. Kinda defeats the purpose of why I like boating: find a nice quiet spot to relax.
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Old 07-30-2015, 09:38 PM   #16
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I am not surprised that your engine alternator only supplies 6-7 amps underway. It is an internally regulated, fixed voltage type and that is about all you can expect unless the battery is very discharged.

But I am surprised that the shore power charger while powered by the generator only adds a few amps. How many amps is it and is it a modern three step charger. But even at 9 amps that load is probably being totally supplied by the charger. The voltage is higher than the set point of the engine's alternator- about 13.5, so it won't add any more.

A 40-60 amp charger (about all that a 2KW Honda can power) should be putting out 20 or so amps and the voltage (check on your battery monitor) should be 14 or more, unless the batteries are 90% full.

So look in to the charger, check the charging voltage while it is powered by the generator- should be about 14, and then consider adding more batteries while on the hook to keep from running that noisy generator.

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Old 07-30-2015, 09:47 PM   #17
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Quote:
Originally Posted by Fotoman View Post
Lots of great input. I do have a Xantrex battery monitor, that's how I know the alternator gives less than what I consume while anchored and I have a deficit after each day. I did try to run the generator while underway today and it does provide a boost (or the 120 volt charger works better than the alternator). I have a 50amp alt but I never see more than 6-7 amps being provided to the batteries. Not sure if this is how it should be. When I ran the generator today it went up to 9-10. Not a huge difference but on the course of an entire crusing day it would make a difference. The generator works a lot harder though so I'm not sure I'll be doing that anyway. For me running the generator while on the hook is out of the question. Kinda defeats the purpose of why I like boating: find a nice quiet spot to relax.
Something doesn't sound right there, Fotoman. If your house bank is depleted to, let's say, 60% and you provide a charge from a 50A charge source, the battery should accept most if not all that charge. I'd be suspicious if the most I can pump into the bank is 9-10A with both charging sources running.

Your bank should accept near 50A from your alternator until the batt voltage reaches the charge voltage of 13.8-14.2V. Then you should see the amps drop as the voltage regulator keeps the voltage at the preset charging voltage.

Maybe your battery bank is weak? Low on water? Loose connections? Sump'n ain't right.
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Old 07-31-2015, 06:49 AM   #18
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"I have a 50amp alt but I never see more than 6-7 amps being provided to the batteries. Not sure if this is how it should be."

The big question is what does the alt see when charging,

If it sees the start batt (usually near 100%)and then the juices is fed to a transistor type unit to top the house batts , thats your problem.

Simple solution is to deep 6 the transistor charging unit and install a solenoid ($16 at the RV store).

Sometimes with a rotary switch the alt. can be made to see the house batts which need the charge and not the start batt which usually does not.
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Old 07-31-2015, 08:21 AM   #19
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If you are using the portable generator underway your batteries are receiving a charge from two sources. Some of the charger regulators will assume this means the battery is near full charge and will cut back. If you wait until you anchor or otherwise stop the engine and then run the portable generator what is your charging level?
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Old 07-31-2015, 08:34 AM   #20
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Is your shunt wired correctly? All the load and charge feeds have to pass through it to get accurate readings. If you have one bypass lead anywhere the data will be bad. Have you added any cables? If your alternators are set higher than the charger you may not get anything out of the charger.
I have a 40 amp charger that charges three banks, two engine start and a house bank. When I run my genset the charger doesn't put out anything. This occurs because the genset alternator is set at 14.1 volts and the charger is set on hot temperature setting of 13.8 volts. I get around this by setting the charger to a cold temperature setting that increases charge voltage set point to over 14.5 volts. The genset alternator only charges the genset start battery which is also Stb engine start battery, which is isolated and cant be tied to other banks.
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