Can I charge and invert simultaneously?

Having a brain stall here....

The question: Can I connect a regulated alternator directly to the battery bus to which my inverter also is connected?

Background: All house batteries are wired to 2 busses; all negative terminals meet at the negative bus, and all positive battery terminals are connected to the positive bus. The inverter/Charger is connected directly to these same busses, and draws battery power for inverting.

Restated: Can I connect my alternator directly to the pos and negative busses so the engine charges the batteries underway, while using the inverter at the same time?

Yes assuming an internally regulated alternator. If externally regulated alternator the it would be the regulator connected to the bus.

It works fine. That is how you make toast while the engine is running!

Yes, it's internally regulated. Thanks for replying. One other tidbit - the alternator is also connected (via separate cabling) to my gen start battery.

Any issues with that? Thx in advance.

Juliet 15 said:

Yes, it's internally regulated. Thanks for replying. One other tidbit - the alternator is also connected (via separate cabling) to my gen start battery.

Any issues with that? Thx in advance.

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Well, your gen battery and house battery are then connected at some point unless you are using a battery isolator. If not then your GEN battery is also part of the house battery.

The gen battery is actually connected to a totally separate bus system. The house bank has its own separate bus that connects just the inverter to the house batteries.

If I understand correctly, the alternator is connected to two busses, one belonging to the generator and one belonging to the house bank.

This would mean that the generator bank is part of the house bank. Such an arrangement would kill the generator battery overtime and leave you in a situation were you couldn’t start the generator when you needed it most.

A generator battery should only have the generator’s alternator connected to it. Connecting an independent shore charger is acceptable.

Okay, I understand. The alternator would actually serve to connect both banks.

tiltrider1 said:

Yes assuming an internally regulated alternator. If externally regulated alternator the it would be the regulator connected to the bus.

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In the externally regulated example given above, where does the alternator's B+ terminal connect.

Does the location of the regulator make any difference with respect to where the alternator's B+ is connected?

luna said:

In the externally regulated example given above, where does the alternator's B+ terminal connect.

Does the location of the regulator make any difference with respect to where the alternator's B+ is connected?

Click to expand...

No, it doesn't make any difference whether internally or externally regulated. How you regulate, and where you direct the charge power are really two independent things.

A picture is worth a thousand words. Any one else confused?

I suspect (hope) you'd find some sort of isolator/combiner between the house bank and the generator start battery. If not then you basically don't have a generator start battery. It starts off the house bank, assuming there's enough juice left in it. Not a good arrangement.

CaptTom said:

I suspect (hope) you'd find some sort of isolator/combiner between the house bank and the generator start battery. If not then you basically don't have a generator start battery. It starts off the house bank, assuming there's enough juice left in it. Not a good arrangement.

Click to expand...

Right on that. I have a combiner between the house and gen banks. The gen battery gets charged but doesn't discharge. That's my backup in case all the other batts go flat.

The inverter doesn't care if the engines are running or not. In fact if you're running a large AC load running the engine will stop the batteries going down as fast. I used to do that on the sailboat due to it's small battery bank.

Juliet 15 said:

Having a brain stall here....

The question: Can I connect a regulated alternator directly to the battery bus to which my inverter also is connected?

Background: All house batteries are wired to 2 busses; all negative terminals meet at the negative bus, and all positive battery terminals are connected to the positive bus. The inverter/Charger is connected directly to these same busses, and draws battery power for inverting.

Restated: Can I connect my alternator directly to the pos and negative busses so the engine charges the batteries underway, while using the inverter at the same time?

Click to expand...

This seems like a rather odd question as it would be unusual for an electrical system not to charge the inverter bank while running the engines, unless you have a large PV array on your boat like s/v Jedi.

If indeed at present the alternator is not connected to the inverter bank there must be a (good?) reason. One such reason could be voltage.
In the day Hatteras built boats of this size with a 32 volt system, which included 32 volt alternators and battery banks. Any small 12 volt load was satisfied by a voltage converter. As far as I know Hatteras did not install inverters, for ac you ran the genset.

How much, if any, of this 32 volt system still exists on your boat would need to be confirmed and the distribution wiring identified. You may still have at least one 32 volt alternator to charge the start bank, if it remains at 32 Volts.

The inverter bank is likely not 32 volts, although thats not impossible as Outback and Analytic Systems may still produce 32 volt inverters.
It's more likely that your inverter's battery bank is 12 or 24 volts and the voltage of the alternator that you connect to the inverter battery bank must match the voltage of the battery bank. Period.

What is the output voltage of the alternator? Voltage of the inverter bank?

To answer your original question, ie connect directly, no you can't, even when the voltage matches.

In order to be considered an acceptable installation the suitably sized wire from the alternator must first connect to an on/off switch, then to a correctly selected fuse that is mounted close to the battery bank's buss and then to the buss itself. Is that direct?

The Hat has a 32v system, and most of it was 32v, including the house when i got it. I've slowly converted most of it. The only 12v things on it were the Gen start systems (3 generators) and the nav systems at the helms.

The port engine alternator existed to charge the gen batts.

i built a new house bank, 1700ah 12v AGMs, and connected it to a new Victron 5000w inverter charger. Shore power or any of the generators will charge the house bank (and everything else).

I have some long distance cruises coming up. I did the math and realized that if I could connect the 12v alternator to the house bank I could keep it and the gen start batteries charged while travelling, hence the consideration.

I wonder about simply putting a switch between the alternator and the house bank so I can connect the alternator when needed.

I have a solar setup planned for the days I'm not underway. My goal is to be able to swing on the hook for 5 to 7 days before need to recharge.

What voltage are the starters on the main engines? If they are not 12 Volts, what device charges the batteries for them?

Everything on the boat is powered by 120/240v except nav equipment and nav lights.
I have a 48v inverter bank and separate 12v banks for starters, etc. Twin mains each have a 12v and 48v alternator. Alternators, bank, and inverter are connected. My inverter is always on. When cruising, the 48v alternators keep the inverter bank charged.
Magnum inverter charges when on shore or generator power. When power is cut, inverter takes over supplying 120/240v without power loss. If inverter bank gets low, inverter will start a generator and inverter charges. When fully charged, inverter stops generator.
My 48v bank is big enough at anchor I can go several days. I usually make water, do laundry, dishwasher, etc., every 2-3 days and run a generator then. I never run a generator when cruising.

The starters are 32v. Each engine has a 32v bank of its own. There's a Sterling 32v charger that charges them when connected to shore power or running a genset. When underway, one 32v alternator on each engine charges them.

So, bottom line, I think I need to install some type of isolation switch that allows me to
1. charge both 12v banks (gen batts and house bank), and,
2. Isolate the house from the gen batts when the alternator (engine) is not running.
Or install a 2nd 12v alternator dedicated to the house bank.

Right?

That is one way to do it and a Blue Seas ACR should fit the bill.

I don't know how much good it would do, as the existing 12 V alternator's original purpose was to charge the 3? genset's batteries its output is likely rather small. Plus is is probably not designed to run flat out for hours charging a 1700 ah bank. If so, it will cook itself.

I would consider doing this.

There is no reason in my mind to have the main engines drive an alternator to charge the genset's start batteries even if the gensets themselves don't have alternators. If that is the case then an ACR fixes that problem. This frees up one mounting location on one engine for a durable 12 V alternator.

In a similar vein there is no reason for each engine to have its own 32 V alternator to charge just its start bank. One 32 V alternator and the appropriate cabling will easily charge both start banks. I charge quite easily with one 24 V alternator, 2- 2,000 MCA start banks, one 3000 MCA thruster bank and a 460 ah inverter bank. The alternator is sized at 100 amps only due to the inverter bank, otherwise a 30 amp alternator would be just fine.
That frees up another alternator mounting location on another engine.

Now that you have 2 open alternator locations I would select matching 12 V alternators sized as to not exceed the drive belt limits (changing drive belt design can be an expensive nightmare) and that fit the mount and space and run them at about 80% of their rated output by way of an external regulator of your choice.

If the drive belts are a single 1/2" V belt this would get you about 160 Amps going into your 1700 ah house bank while you cruise along at 7 knots with the alternators spinning at 5000 RPM.

You might look into a ProIso which directs the current as needed. Also on my Victron Inverter I can switch between charge/Invert/Both.

I've been specific to the batteries/systems involved in my question to avoid complexities. Here's the rest of the story. Apologies for the length.

The boat was originally only 32v. Each engine had a 32v bank of its own One served as the house, one as the start. You could switch between them. There was a Heart 200w inverter attached. I don't know what the original genset stupid was.

Some PO installed 2 new 12v 15kw gens in 1996. They installed an 8D 12v start battery for each gen. Then they installed a Furuno NavNet3D 12v nav/radar/depth system, and connected it to the 12v Genset batteries. That's why there's an alternator to charge the genset batts. To power the nav while underway without depleting the genset batts.

Since I got the boat ~6 yrs ago I've added the large house bank and eliminated most 32v items, or stepped them down to 12v. But there are still some items (Naiad stabs, and old depth sounder, some LED lights, nav and anchor lights, a compressor for the horns, two water pumps instrument backlights) that still use 32v off the engine banks. That's why there are still 32v alternators.
And the engines will always need 32v to start.

I'm installing 800w solar to charge the big house bank when on the hook. But that won't charge the bank very fast, and I don't have the room or desire to add more. My goal is 5 to 7 days with no genset.
Lastly, I think it makes sense to be able to charge the big bank when I'm on long legs underway, so I'm looking at ways to do so. The 12v alternator is 105 amp, more than enough for the genset batts (powering the nav systems I use when underway), so I'm thinking about ways to apply that alternator to the house bank.

Whew. WTMI, I know.

Oh, the PO also installed a 3rd genset, a small12v, 4kw one. It's only purpose is to charge batteries, 12v and 32v.

Ok, let’s not talk about the 2-32 V alternators anymore and just accept the fact that they are going to continue to be utilized although they are basically doing very little work.

If I understand you correctly you have a new 1700 ah 12 V AGM house/inverter bank and would like to hook it up to a 105 A internally regulated 12 V alternator.
The use case includes being on the hook for numerous days, using your 800 watts of solar generation capacity and having the alternator help charge the house bank while underway.

The fly in the ointment is the fact that the existing 12 V 105 A alternator is likely designed to charge a start battery and provide a small amount of power to run the lights, heater, and radio in your car, not run flat out into a large depleted battery bank for 5 hours or more.

You need to throttle the output of the alternator otherwise it will fail.

There are at least 2 methods to do this:

Control the output from the alternator by using an external regulator set to allow the alternator to produce only the amount of power it can while keeping itself cool enough not to fail.

Or do this.

Control the load on the alternator by using a DC to DC Charger, set to load the alternator close to the max. it can produce and still survive.
You need to include the existing loads, Nav, lights, etc. in this calculation.

You may have one other problem.

The existing 12 V 8D genset start batteries are likely flooded lead acid not AGM.
The flooded 8Ds may survive well enough using the specific AGM charge setting for your new AGM bank. You need to check on this.

If you are not happy with that compromise, have the existing alternator continue to charge the 8D, install the DC to DC charger between the 8Ds and the new AGM bank, set the max. load allowed and the charge parameters to whatever your new AGM bank requires and you are done.

If it was me, I’d likely do neither and just run the 4kW genset to power the chargers until I could design and install a complete battery system.

Luna, thanks for taking the time. I appreciate working thru this with you.

I understand the options you listed out. Right now, that's what I do - run the little gen as needed.

I'm considering replacing the alternator with a larger one. In either case, how does one determine the max continuous output for an alternator?

Also, JackConnick suggested a ProIso. I hadn't heard of it, so I looked it up. It seems to fit this situation exactly, except for the problem you pointed out of potentially shortening the life of the alternator. Are you familiar with these digital isolators?

Determining the safe max. output of an alternator can be complex or if you are comfortable with using the alternator temperature sensor found on most external regulators, simple.

First let's conclude that your existing alternator has no ability itself to actively reduce output as a function of temperature, although some do in an effort to save themselves even though they are internally regulated.

You need to determine from the alternator manufacturer what is the max allowable temp. and where on the alternator is that temp. measured.
According to Delco, my 40si is rated at 257º F at the center of the rear air intake. I actually questioned the location and had it confirmed in an email from the Engineering Dept.

The simple way is to set the temp. sensor of the external regulator to something less than the rated 257º, and mount it on the assigned location on the alternator. Plug it in to the regulator, program the regulator and you should be running at the max. allowable output at all times based on alternator temp.

If you are only using a DC to DC charger things get a little more complex and subjected to a bit of trial and error.

First we need to quantify what the max. load on the alternator is without any charging going on other than that required to support your running loads like Nav. lights and equipment, radar, sounder just the regular stuff. Let's say that load is 25 Amps.
You have an alternator with a name plate rating of 105 Amps.
So that is 80 amps of potential charging, but some of that is unusable long term due to heat.

Victron makes a 50 Amp DC to DC charger that will likely do quite well in your situation.

I would start with the charger programmed for the charge parameters of your new AGM inverter bank and the output of the charger limited to 25 Amps. That loads the alternator at a total of 50 Amps or about 50%.

With a depleted inverter bank go for a cruise at your normal speed and monitor alternator temp. with an IR gun or better yet a thermistor and a meter. Run for 2 hours with the alternator outputting 50 Amps to establish a stable alternator temp.

If you have headroom on the Temp you might want to reprogram the DC to DC to output 35 Amps and retest.
You could continue to step up the DC to DC's output current (which is a load on the alternator) until the 50 Amp capacity is reached which would put a 75 Amp load on the alternator.

If your alternator is still cool (doubtful running at 70%) you could then add another DC to DC charger and add more load to the alternator.

How close to cooking it you want to run is up to you.


As for me, I run my 257º rated alternator at a 185º max temp and have the regulator derate the alternator as required. This derate does not happen too often as I happen to have a cool running engine room with lots of cool air flow directed at the alternators.
I am not a fan of running electronic things at anywhere near their max temp, but that is just me.

I quickly looked at the Prolso which is some kind of progressive combiner/isolator and don't see the usefulness of the product.

The pro Iso appears to allow one alternator to smart-charge multiple battery banks. It appears to turn an alternator into a multi bank smart charger.

The Prolso appears to be a sophisticated switch that is intended to connect the charge current to first the start battery and once that battery is at 13.3 volts the switch connects the 2nd battery. Once the 2nd battery is at 13.3 volts the 3rd battery is connected. I don't think you can change any voltage settings.
It's unclear if any battery is disconnected when a new battery is connected in order to provide as much charge current as possible to the newly connected battery. I doubt that actually happens, as the switch would then at some point have to determine when to reconnect the disconnected battery.
The Prolso does however do something similar when one of the connected batteries (say the thruster bank) is heavily loaded and sees a voltage drop. The Prolso will then disconnect all other batteries leaving only the loaded one connected and when that connected battery gets back to 13.3 volts it will start the progressive connecting sequence, start battery first, once again.

The Prolso does not alter the values of the charge voltage or current, it simply connects batteries to the circuit. The Prolso has no ability to protect the alternator from cooking itself, and in fact it does just the opposite by adding load to the alternator by progressively adding depleted battery banks.

If the output of the alternator is dumb, (most internally regulated alternators are considered dumb) running the alternator's output through a Prolso won't change that.

The Prolso does have a use for those who charge multiple battery banks with solar, a shore power charger or alternator that each only have a single output. Hopefully in this case the charge profile is already smart.

I sent you a PM to see if you're available to talk by phone. I appreciate very much your help. Talking might make it easier to clarify some things if you're available.

50 minutes after your PM, I sent you a PM in response. Check your TF mail. Send me an email or a PM as to what time is good for you.