Charging with Engine Alternator

[dpaquin]

I don't quite understand how the engine alternator charges the batteries on my 42 Hunter with the optional Inverter/Charger. I was motoring and inverting for 2 days this past weekend and my main house batteries were depleted. I had assumed they would be charging while the motor was running, but apparently not. It seems I cannot charge and invert at the same time. Is that true? The engine alternator puts out 12 VDC (I think). Where does that tap in? I don't see it on any schematics.

 

[capejt]

It's all about balance

First thing, you probably shouldn't use the inverter when trying to charge the batteries. Find out how many amps your inverter is sucking down while operating, and compare that to how many amps your alternator is pumping out. Also, take into account anything else running off the DC circuits while "charging". Engine alternators are not famous for cranking out a lot of power. In the grand scheme of things it's almost more like a trickle charge.
Consider a car and its charging system. I'll bet you'll find that the majority of people who have problems with the battery starting the car are people who drive primarily at night when the load of headlights, and other drain sources are being utilized. Yes, it's true, on a car, even driving at night, there is a continuous charge from the engine, but take into account the drain being put on the system at the same time. Detroit doesn't really take this into account when designing systems.
Let's say (only as an example) that your battery is down about half way. Your alternator puts out let's say 90 amps. Further, let's say your inverter is sucking up 40 amps, you also have instruments, radar, refrigeration, etc. totaling another 40 amps. Guess what? You only have 10 amps going towards charging the battery. For an average marine battery I think you're looking at running your engine for 12 hours or more, and even then you might not have a full charge.
I would suggest a full day and night of shore power charge without the inverter running, then try again with a fully charged battery.

 

[Don Lucas]

What were you running while using the inverter?

How fast was you engine running?

Does you regulator work? Is your alternator working?

What does the alternator supply go though on the way to the battery (switches, isolators).

No reason (on my boat at least) that you can not use the inverter and charge via the engine at the same time. But on my boat it does matter what position you have the inverter selector switch while doing it as the switch besides selecting which battery is supplying the inverter also determines which battery is charged from the alternator.

So how is your system wired? Do you even know?

 

[dpaquin]

I was running at about mid power at around 1800 rpm. Running very light AC loads.

I am not totally certain how it's wired - that is what I am trying to find out. I can't tell if the engine alternator charges the batteries directly or if it uses the inverter/charger unit.

 

[seadaddler]

inverter/charger

I will try to help but not a expert at this for sure and if wrong some one correct me.
The alternator does not work with the inverter/charge and charges the batteries by itself and inverter/charger charges only off shore power or gen.
First off check is the alternator battery wire going to the house bank ( I have the alternator wire go to my house bank) or the alternator goes to your battery
1/2/both switch and you set the switch at both should be charging your house bank and if another bank like starter battery.
You will need to check your wiring,what inverter/charger do you have and do you have a remote panel that you push for charger or inverter.
Nick

 

[Claygr]

Re: inverter/charger

Your alternator should be putting out 14 volts. You most likely have at least an analog voltmeter on your engine panel what should jump up from the 12 volt range to the 14 volt range when the engine is started. If it does not, you have a problem with your alternator.

My guess is that your alternator output either runs directly to your house bank or runs to the common post on the battery switch. I can't see any reason why the alternator output would run through an inverter/battery charger.

I don't know what the amperage rating is for your alternator or what you were drawing from the inverter and other DC sources. I am sure it is possible for the amp draw on an inverter plus other DC draws to exceed the recharging capacity of an alternator but I would think that this would be part of the installation consideration for Hunter or the dealer - an inverter with that much amp draw is going to be inviting just this sort of problem. My guess is that you have an alternator problem.

 

[Don Lucas]

Well that is your problem. If you don't know how the system is designed/wired it isn't really possible to help you other than telling you to check the alternator/regulator to be sure they are working. But I would suspect if you didn't already know this that saying to check it wouldn't help you.

The charger/inverter has nothing to do with the alternator except for maybe a switch position.

Turn the inverter off and run your engine and check the voltage at the batteries. Let us know.

 

[BayMan]

Related question- let's say the battery selector is set for the house bank or the starting battery but not both. When you start the engine that way is the alternator charging just the selected battery or both?

 

[Claygr]

If the alternator output is run to the common post on the battery switch, only the selected battery will charge. If the alternator output is run to the house bank, the house bank will always charge and the starting/reserve battery will only charge if the switch is set to "both" or "all." This is assuming that you don't have an automatic charging relay or a similar product to pass charging load between the house bank and the starting/reserve battery independent of the battery switch.

 

[Don Lucas]

Related question- let's say the battery selector is set for the house bank or the starting battery but not both. When you start the engine that way is the alternator charging just the selected battery or both?

Impossible to answer other than maybe. On my Hunter the start battery has its' own breaker and it isn't part of a 1/2/both/off switch. The 1/2/both/off switch is for the inverter supply only as there are individual breakers for the house supply to the main DC panel. But the inverter switch besides selecting the battery supplying the inverter also determines which batteries will charge from the alternator.

But that is on my 410 as there are different arrangements for the 410 depending on the options the boat came with.

The only people who can really answer the OP is someone with the same boat and options.

 

[Benny17441]

Hard to tell without knowing your wiring configuration. A dealer or a prior owner could have modified the manufacturers configuration. I know some folks that direct the alternator output exclusively to the starting battery and recharge their house bank from shorepower or an onboard generator. (it works for them) You may need to disconnect your shorepower charger, shut off all DC loads and allow the batteries to rest for at least one hour then take a voltage reading across the battery terminals. The reading should be in the range of 12V or ideally close to 12.6V. Then start up the engine and take another reading. If the alternator is charging the bank then the voltage should jump up to the 13V-14V range. If the reading remains in the 12V range then it is not. Next bring the inverter online with a light AC load and take another reading an observe if the charging voltage cuts off or just diminishes a tad. Our engines are small and they are usually paired with small alternators to minimize horsepower losses. They have to work hard and their hard work produces heat which reduces their efficiency. At reduced RPM you could be getting only half of their rated output. If you discharge a battery to 50% it will take you on the average 5 to 6 hours of running time to recharge it to around 90%. The batteries have a rate of acceptance which diminishes as the batteries approach full charge slowing down the process.

 

[ttac]

Hello, I checked to see where my alt feed went to and took a photo of our system! I don't know if this will help.

This is a multi battery isolator. And the alt wire is the lower one. There are 5 terminal's on it. Hope this helps.

 

[dpaquin]

Block Diagram

Thanks for all the help. One of my goals here is to create a simplified block diagram of my electrical system. I have attached it here for anyone's review and comment.

 

[seadaddler]

1-House bank

I never did like my factory setup which had 2 banks of 1 -4-D each bank and no start battery and was OK but needed to switch between the 2 banks for charging and so I changed to 1 bank and now have 4-6 volt as my house bank
and added 1 start battery with alternator wire to the house bank and have 2- large solar panel to a charge control to charge my house bank and it also charges the start battery.
I don't like battery isolators either,I do have a inverter/charger and FP Gen.
Nick

 

[ice breaker]

On most new boats there is a cross tie solenoid that only is energized when the motor is running and charging. When the motor is off it opens the circuit to prevent the starting battery from being drained along with the house bank. These solenoids do get burned contacts and may need replacement. When you have the engine running you should see very similar voltage on the start battery and the house bank. If the house bank is not coming up, you may want to jumper around the solenoid to see if the house bank then shows similar charging voltage. Good luck.

 

[Don Lucas]

Thanks for all the help. One of my goals here is to create a simplified block diagram of my electrical system. I have attached it here for anyone's review and comment.

Looks similar to my boat's system, but not quite. I don't think your drawing is right as in it the start battery never charges from the alternator.

And it is a fact that my house batteries can supply the start battery loads even if the start battery breaker is off. I wouldn't be surprised if yours will also.

But you never have told us what you found out as to why your batteries weren't charging on the alternator.