How to integrate a portable generator?

[Epicurean]

My solar charging system is quite simple and almost always gives me enough power. It involves solar panels, MPPT charge controller, and Li batteries. There's currently no provision for a DC or AC battery charger. But I'm thinking of doing an ocean crossing where besides the added drain of navigation equipment and AP, I may be in areas with heavy cloud cover for days at a time. So I'd like to get a little gas genset to charge the batteries just in case. Where/how do I plug that in to my system? In terms of gas consumption is the generator's DC output or driving a little battery charger more efficient? Thanks.

[Singularity]

Not answering your question, but have you ruled out a 12v towed generator and/or a propshaft generator?

[fxykty]

Originally Posted by Epicurean

My solar charging system is quite simple and almost always gives me enough power. It involves solar panels, MPPT charge controller, and Li batteries. There's currently no provision for a DC or AC battery charger. But I'm thinking of doing an ocean crossing where besides the added drain of navigation equipment and AP, I may be in areas with heavy cloud cover for days at a time. So I'd like to get a little gas genset to charge the batteries just in case. Where/how do I plug that in to my system? In terms of gas consumption is the generator's DC output or driving a little battery charger more efficient? Thanks.

Your profile shows you have a Mumby 48. Is it a new build or is it stripped and you are rebuilding it?

If it has motors and alternators on those motors then that’s a ready source of DC power and all you’d need to add is a DC-DC charger with a lithium profile. Probably worth optimising that before purchasing a generator, unless you want a generator for something else.

Otherwise, do you have a shore power plug (probably not, if you don’t have an AC battery charger)? If you do, that’s where to plug in a portable generator.

If you get a generator that outputs DC at a high enough voltage (minimum 18V if charging a 12V battery) then you could output the generator DC into another solar controller. Or a DC-DC charger, which may be simpler if the generator can’t output 18+V and likely less expensive than a solar controller.

You could install an AC charger, but it sounds like that makes your system more complex than you want.

[Epicurean]

Yes, I can charge from the engine alternators. I don't like to run the engines for that purpose but I can/have. One problem is I can't lock the transmission when doing that. Anyway, a gas generator is another layer of redundancy. I had a towing generator on a previous boat. It was a wild beast! For as infrequent as I need extra watts it's not worth the expense or complication.

[Reefmagnet]

If you're talking a Honda, the DC output is pretty much useless. With LFP you need a decent charger with the correct charging profile anyway. Easiest solution is to charge via a mains charger. On my boat, I have a shore power connector and a mains charger and I just need to plug the generator into that to charge the batteries. Prior to having a shore power connector, I just connected the charger directly to the battery with alligator clips and plugged the charger directly into the generator.

[Epicurean]

Originally Posted by Reefmagnet

If you're talking a Honda, the DC output is pretty much useless. With LFP you need a decent charger with the correct charging profile anyway. Easiest solution is to charge via a mains charger. On my boat, I have a shore power connector and a mains charger and I just need to plug the generator into that to charge the batteries. Prior to having a shore power connector, I just connected the charger directly to the battery with alligator clips and plugged the charger directly into the generator.

So then just connect the charger output directly to the battery. Generator==> charger --> battery. It's totally independent of the solar charging circuit.

[markcouz]

The DC output on most portable gennies is a small fraction of the gennies AC output capability (eg 10amps at 12v = 240W on a 2kw gennie), also the voltage is too low for direct charging use, but could be used via a DC-DC charger.

I would recommend getting an AC-DC charger that is programmable to your battery chemistry charge profile, so that the higher AC power output can be used.

[markcouz]

Apologies, pretty much duplicated Reefmagnet feedback.

[Epicurean]

Originally Posted by markcouz

The DC output on most portable gennies is a small fraction of the gennies AC output capability (eg 10amps at 12v = 240W on a 2kw gennie), also the voltage is too low for direct charging use, but could be used via a DC-DC charger.

I would recommend getting an AC-DC charger that is programmable to your battery chemistry charge profile, so that the higher AC power output can be used.

I get your point. Since I only want this for battery charging I probably won't go for 2kw, perhaps 650w. I assume, although I could be wrong, the DC output lower wattage consumes less fuel then the higher output needed to drive an AC-DC charger. which is more efficient? Of course, the time spent listening to the thing is worth something.

[markcouz]

Lower power output will use less fuel but be less efficient than using higher output and faster charge (gennie still uses fuel producing zero output).

I would aim for around 75% loading if the gennie has a single specific use.

[Epicurean]

That sounds reasonable. But in practice what does that mean? So, Lithiums are full around 14.4V, I think. A 650 W (continuous) generator would put out 45 A @ 14.4 V. 75% of that is 34A. So maybe a 30 A AC-dc charger?

[markcouz]

AcDc charger of around 30amp @ 14.4v would be about right on a 650w gennie.

[Tupaia]

Originally Posted by markcouz

AcDc charger of around 30amp @ 14.4v would be about right on a 650w gennie.

If you go for a 650w gen then there is an issue if it an Inverter type or not.


An old style non inverter, really cheap will run a multi-voltage battery charger (eq Sterling 90-300volt) because the gen will continue to run even if it cannot produce it's rated voltage.



An inverter gen will cut out if it cannot output the power draw at rated voltage.


You also need to take account of the Power Factor. For example a 650w gen should be able to support a 40amp charger 650/14.5 but it will not because of the PF (eg 0.7) this would be more like 30amp.


You could go for something like an Alten DC gen 55amp then you would not need the AC circuitry.

[SRQsailor]

I use a Honda EU 1000i, output to shore power connector. Unless you can install it in a ventilated compartment, be certain you run it on deck with no possibility of CO collecting in the cockpit or salon. Get a good CO detector or two and place them anywhere you might be while the generator is running, including the cockpit. Be safe. Smooth sailing!

[henryv]

You need to be able to dial down the input current on your battery charger when using a small generator. My Xantrex charger/invertor has a remote panel that lets me set the maximum input current. If I don't set it low the generator overloads and kicks out it's circuit breaker.