Charging question

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Fotoman

Fotoman

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Nov 12, 2009
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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?
 
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?
 
markpierce said:
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?
Click to expand...


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.
 
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.
 
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?
 
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.
 
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.
 
"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.
 
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
 
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.

David
 
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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.
 
How about installing a battery monitor? That will let you know exactly what is going into and out of the batteries.
 
Or better, a clamp ammeter
 
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.
 
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.

David
 
Fotoman said:
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.
Click to expand...

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.
 
"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.
 
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?
 
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.
 
Charger, alternators etc are not constant current devices. A 40 amp charger has a max current of 40 amps but will deliver much less except under certain conditions and briefly.The cut back current as the voltage increases on the batteries. Battery voltage increases as the charge increases depending on ability to take charge, called acceptance rate. As batteries age or wear out the ability to accept charge decreases meaning the voltage increases sooner.


Are your batteries getting long in the tooth?? Are all connections clean?
 
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Do you have a diode isolator between the house and start batt?

Does your alternator output go to your hot lug on the batt switch?
 
I don't have a diode, I use a Echo charger for the start battery and yes the alternator wire goes to the lug on the main switch. Can that make a difference?
 
Can that make a difference?

IF the rotary switch just selects engine start batt 1 or start batt 2 No

But if on one terminal is the start batt , and the house is on the other, charging will frequently be poor.

This is because the alt V reg sees the voltage of both the almost full starts and the 1/2 dead house.

Slow charging is the result , esp with a stock vehicle V regulator.

IF you select house alone , the charging will get better as the alt regulator now sees the discharged house.

Sadly the stock V regulator does a lousy job on 1/2 dead batts,

The 3 or 4 stage marine regulators are worth the expense.

Any rotary switch must be the field disconnect style (two little terminals on the back) to keep from frying the alt should someone switch to OFF , with the engine operating,

"Stuff happens"
 
Fotoman said:
I don't have a diode, I use a Echo charger for the start battery and yes the alternator wire goes to the lug on the main switch. Can that make a difference?
Click to expand...


Wire the alt. direct to the house batt. use large wire to minimize voltage drop. Let the Echo charge take care of the start batts. independent of the house. Someday change to a high output alt. with a smart charge direct to house as well.

Only have starter batts. hooked to starter and everything else to the house bank. Have the switch only to the starter and use ut only to cross feed the house to starter if needed. This way the system is foolproof you never need to touch the switch and you can't run down the start battery bank with any house loads.

Solar to house bank as this will also maintaine start when making current via the Echo charge
 
Thanks Scott. Except for the alt being wired directly to the house batt, that is pretty much the setup that I have. When I got the boat one of the first things I did was to change the alt wire to a bigger size (#10) to make sure I got the maximum juice. I did wire it to the switch lug but my switch is actually never used. I have 2 house banks but only use the first one. The other one is there as a backup (kept the original batts and bought new ones for bank 1). I have a dedicated starting battery that is charged with the echo charger from house bank #1. So apart from sending the alt wire directly to the main house bank, that's it.

The only other thing that I see as being a potential problem is the wires that connect my 2 4D batteries together (house #1). There is a bit of green stuff on the terminals and they are old wires. Just ordered new ones so I'll be able to replace them and see if that makes a difference.
 
Sounds like the 2 units are sensing each other and cutting the amperage right back to tick over.
 
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