KW output question

[Delta]

The title of the thread is to make me sound "not so stupid." I did have an Onan 7.5 KW genset. I like 50 amps of service when at sea so the 7.5 gave me that. I will be replacing that as well as my engine. The boat is thirty years old and, of course, with the Prosine 3KW inverter/charger I can get a certain amount of 110V juice. Here's my question: Can I get a smaller genset, be running that genset and charging the batteries with the Prosine and use the output from the generator AND inverter together to give me the amps I need? Or can I only use them separately? Please forgive my ignorance!!!!!!

[KnottyBuoyz]

If I were to hazard a guess, I don't have the reference material in front of me at the moment, you have to isolate your AC supplies (AC Selector Switch). In other words, you can't supply your AC house loads from two separate sources, generator and inverter, at the same time. You could, if wired correctly, charge your batteries from your generator and supply your AC house loads from the Inverter. With this approach you might ad to the bulk charge but run the risk of severely undercharging your batteries. You would probably want enough generator capacity to run all your AC house loads for peak periods and switch to inverter when the loads drop (ie. after diner). Ideally you'll want to charge your batteries when AC loads are minimal to prevent undercharging. Sometimes I think it's more black magic than pure science! *lol*

[marshmat]

Hi Delta,

Can I get a smaller genset, be running that genset and charging the batteries with the Prosine and use the output from the generator AND inverter together to give me the amps I need?

The inverter runs off the batteries, and so of course cannot charge them.
It is possible to split a large house load between a genset and an inverter, provided the inverter is capable of closely matching phase and amplitude to the genset's output. Such inverters exist but are very expensive; yours is not one of them (they are sometimes called 'grid tie' inverters, and are almost never used on boats).
I would size the genset so that it will be reasonably well loaded in normal conditions (they don't like running with low load, or idling). Make a list of the gear you want to power with it, and sort by what will be running simultaneously and for how long. This will give you a better idea of how much genset you really need.

[StianM]

I tink this is close to imposible. If you had a big inverter with large output the generator's Hz would be forced to folow the inverters curve.

I think I would rather split the power in the boat with a switch so the generator could supply the whole ship, but under peak power loads on one side off the switch could be isolated from the generator and supplied bye the inverter instead.

[TerryKing]

Originally Posted by StianM

..(snip)..I think I would rather split the power in the boat with a switch so the generator could supply the whole ship, but under peak power loads on one side off the switch could be isolated from the generator and supplied bye the inverter instead.

I agree. Separate the big loads like A/C etc. that do not have to be full time from those that the inverter can handle with the Genset off. That way those separate AC circuits do not have to have the exact same frequency and phase (portion of a cycle). Some loads could have a double-throw switch so they could be run from either source. Do NOT use two switches!! The first time anyone flips both at once the two Sources would be tied together with probably damage.

[StianM]

Buy a syncronoscope from Deif or Megacon don't cost mutch and simply install breakers with time relay.

Just alow the brakers to be closed when the frekvensy match and brakers are triped within 5sec or something.

[Delta]

Yeah, I could live with that. Say, for example, I just wanted to run the water heater for an hour or the refrigeration. Could I separate that to the inverter and keep the AC units and lighting and maybe TV off the generator? I'm trying to make some space in my Whitby engine room!!! Grrrrr.

[Ike]

Geez. Sounds to me like you're chasing your tail here. You would have a serious mess of redundant wiring and switches to isolate circuits so that some could run off the inverter and some off the generator. As was said before, you cannot have two sources of power going into the same system at the same time, you are talking serious shock hazard and fire potential. Any circuit you want to power off the inverter while running the rest of the system on generator would have to have some means of isolating that circuit. Usually this is done by means of a power transfer switch that automatically turns off the power from one source and turns on the power from the other source with only a few millisecond delay so things don't stop running. That's what happens when the lights flicker in your house when the power company switches from one power source to another. This is also what happens when you unplug the shore power cord and light off the generator. A switch automatically transfers power.

Now, if the items you want to isolate are not hard wired into the system, that is, have cords that are plugged into a socket, then it becomes easier. You simply have several sockets that are powered by your inverter, unplug the cord from the regular socket, and plug it into the socket powered by the inverter.

[charmc]

Originally Posted by Ike

Now, if the items you want to isolate are not hard wired into the system, that is, have cords that are plugged into a socket, then it becomes easier. You simply have several sockets that are powered by your inverter, unplug the cord from the regular socket, and plug it into the socket powered by the inverter.

That is, IMHO, the only safe and practical way to handle power from multiple sources. The alternative is switch and synchronization equipment that is costly and not intended for marine use on small, i.e. recreational boats. If obtainable, you still have to weigh the cost of a failure. KISS seems to apply here.

[TerryKing]

(We're talking about AC loads here): Maybe I'm missing something here. There are two possibilities in switching a load to another source:

1. The load is disconnected for some time, from milliseconds to minutes. The load becomes unpowered and stops working. This is OK in the particular situation, and the load works again when the power is restored. No hurry.

2. The load needs to operate continuously with no interruption. This implies that the two sources have to be synchronized (same phase / voltage) while the load is switched in a small fraction of a cycle, say 2 milliseconds or so. This implies an electronic switch.

On a small boat, with loads that are not sensitive, like #1, it seems that either double-throw switches that are "break before make" as most switches are would work OK. There are also double-throw switches available that have a center-off position, which would be a good feature. Some switches have a mechanical interlock so that you have to switch them to center off, release the handle, and then throw to an ON position.

The other possibility, which I personally like, is to use twist-lock sockets with short cables and plugs that can be plugged into different sources, or also extension cables.

So, what kinds of loads are we talking about here? Maybe we can agree on types of loads that are not sensitive to being powered off and come right back on, like:
- Lights
- heaters
- pumps

and some loads that will not automatically come back on. Hmmm. Like:

- Microwave ovens
- CD or DVD Players
- computers

Most NAV equipment is DC powered, right??

Can someone who has managed this stuff on shipboard for a while tell us what they did??

[Crag Cay]

There are lots of systems made for running boat's 115 / 240 VAC off a generator with either shore power and inverters at the same time.

The generator / inverter mix is useful so you can size your generator off the steady demand and use the invertor to add power to cope with the peaks. Particualarly useful with onboard aircon.

The other common use is where the shore power connection is not sufficient to power all the dockside demands onboard, so the generator or inverter can be used to suppliment the shore power instead of constantly blowing the marina breakers.

Victron and Mastervolt both make systems.

[Delta]

Thanks, Crag........

[Portager]

To do what you want you need an inverter that will synchronize with the generator so that the power will be in phase such as the Victron http://www.victronenergy.com/. They are expensive, but they are also a very high quality unit and they will do what you want.

We have a trailer with two A/C units and a 6 KW generator that was too small to run the 2 A/C units. Instead of upgrading to a 8 KW generator, we went to a 3.5 KW generator and added a Victron Phoenix Multi inverter/charger. This allows us to run our normal electrical loads plus 1 A/C unit off the battery bank and if we need both A/C units we start the generator. The systems works so well we are installing a one in our Fire Truck which has a 20 KW generator.

[FAST FRED]

The TRACE 2440 has a current matching and boost feature. It will follow the cps of the power source and add what ever is required above an operator pre set amps draw.

These are great as the boat can be plugged into a 15A circuit yet run two air cond , with a good batt set.

Some RV folks have selected the 24V 300A bus alternators as gensets with a used reefer diesel engine. Advantage is HUGE charging ability (battery temperature monitors REQUIRED), and the ability to run the noisemaker quite slowly when not needing full amps.The Trace does easily start 2 air cond.

Graingers has many relays that can be used for "load shedding".

A single wire, say from the fridgefreezer will trip the Hot water heater off , till the fridge shuts down , then turn it back on.
These can be really nice on limited power as once setup will operate with no further operator input.

FF

[Victor Möller]

Just as Portager wrote, the Phoenix MultiPlus from Victron Energy is what you are looking for. If 3KVA is not enough you can use multiple units to get more! If you use 3, you can get a full 3Phase system.

I have used one onboard for 2 years, no regrets!

Make sure to read the Energy Unlimited PDF at:
http://www.victronenergy.com/upload/...yUnlimited.pdf

The Phoenix Multi Control unit is a must have, I can't understand why it is a "accessorie".