Portable Generator as a Backup Power Source

[Bob S]

Portable generators don't do much good if your battery charger is only putting out 20 amps. Even a 40 or 60 amp charger takes too long to get any real benefit (depending on your house bank's capacity). I think a high output alternator (90 - 150A) will charge a bank a lot faster and be more economical. We have a Honda that I bought so the Admiral could blow dry here hair. I never found it useful in charging our house bank. I added 525 watts of solar last season and she can dry her hair with our 3000W inverter and be fully charged before night fall. I think there are many factors and options to consider before making your decision.

 

[dLj]

Portable generators don't do much good if your battery charger is only putting out 20 amps. Even a 40 or 60 amp charger takes too long to get any real benefit (depending on your house bank's capacity). I think a high output alternator (90 - 150A) will charge a bank a lot faster and be more economical. We have a Honda that I bought so the Admiral could blow dry here hair. I never found it useful in charging our house bank. I added 525 watts of solar last season and she can dry her hair with our 3000W inverter and be fully charged before night fall. I think there are many factors and options to consider before making your decision.

I run my portable generator into my shore power connection. That's a 30 amp plug. Hence, that's technically 3600 watts. My Honda is the EU2200i which is rated at 2200 watts max, and 1800 watts continuous. So at 1800 watts output, that's giving me approximately 150 amps of 12 volt DC. This unit does not have a 12V DC output but if it did, I can't see why I'd ever bother hooking it up if it was only putting out 20 amps... When I'm running my engine I have 240 amp capacity, that I throttle down to 160 amp output (approximately) to not over-heat my alternators. I can't imagine any reason I'd want a trickle charger coming out of a gasoline or propane driven engine...

Just my 2 cents...

dj

 

[tfox2069]

I considered converting a Honda generator to run off of propane, but in our area the only places I could refuel with propane were at stores well away from marinas, and gasoline was readily available at every marina fuel dock. Trying to solve the logistics of refueling propane for a generator seemed like way too much of a PITA. Generally I only need to refill a propane tank in between seasons when used for cooking purposes alone. Using one to run a generator would require refilling frequently - perhaps daily (depending on the failure you're trying to counteract and the hours on end you might have to run that generator in lieu of your normal charging source). No thanks.

 

[LloydB]

Having a bit of a problem following this thread just between you and me. However if I was charging a battery at 14.8 volts with 160 amps I wouldn't consider it a trickle charge but that's just me.

 

[dlochner]

Portable generators don't do much good if your battery charger is only putting out 20 amps. Even a 40 or 60 amp charger takes too long to get any real benefit (depending on your house bank's capacity). I think a high output alternator (90 - 150A) will charge a bank a lot faster and be more economical. We have a Honda that I bought so the Admiral could blow dry here hair. I never found it useful in charging our house bank. I added 525 watts of solar last season and she can dry her hair with our 3000W inverter and be fully charged before night fall. I think there are many factors and options to consider before making your decision.

The charger has to match the battery chemistry. A 20 amp charger is adequate for a couple of Group 31 or smaller batteries. The important characteristic is charge acceptance rate, which for FLA batteries is 10-15% of the battery's capacity. AGMs can accept more, some as much as 40%. Lifeline claims there batteries can accept 500C or 5 times the batteries capacity.

Even for AGMs, higher charging rates only have a beneficial effect for the first hour or so of charging a deeply discharged battery. After the second hour, it doesn't make any real difference. Regardless of initial charge rates, it takes about the same amount of time whether one starts at .4C or 2C to reach 100% SOC.

How Fast Can an AGM Battery be Charged? - Marine How To

TEST EQUIPMENT USED IN THIS ARTICLE BUY MHT RECOMMENDED TEST EQUIPMENT - AMAZON Baseline Discharge 49.3% SOC PREFACE: This article looks at the *charging times & achieved state of charge of an AGM battery

marinehowto.com

 

[dLj]

Having a bit of a problem following this thread just between you and me. However if I was charging a battery at 14.8 volts with 160 amps I wouldn't consider it a trickle charge but that's just me.

Yes, the question was connecting the 12V output of a generator that only gives 20 amps of output. That's what I'm referring to as trickle charging.

dj

 

[dLj]

The charger has to match the battery chemistry. A 20 amp charger is adequate for a couple of Group 31 or smaller batteries. The important characteristic is charge acceptance rate, which for FLA batteries is 10-15% of the battery's capacity. AGMs can accept more, some as much as 40%. Lifeline claims there batteries can accept 500C or 5 times the batteries capacity.

Good point - but when running a generator with it's inherence fuel consumption, I'm always looking to minimize time spent charging as much as possible. But maybe it doesn't make much difference... (my case cannot be used, I'm running LiFePo batteries - gave up on the lead acid for house banks - still use them for start and bow thruster/windlass, but I charge those off the lithium house banks).

It would be very interesting to see a graph of the time to charge to various end-points - like 85%, 90%, 95% and full charge - starting with a maximum acceptance rate compared to starting with this 20 amp output. That would be a very revealing graph for this discussion. I don't know how to make such a graph...

dj

 

[dlochner]

Good point - but when running a generator with it's inherence fuel consumption, I'm always looking to minimize time spent charging as much as possible. But maybe it doesn't make much difference... (my case cannot be used, I'm running LiFePo batteries - gave up on the lead acid for house banks - still use them for start and bow thruster/windlass, but I charge those off the lithium house banks).

It would be very interesting to see a graph of the time to charge to various end-points - like 85%, 90%, 95% and full charge - starting with a maximum acceptance rate compared to starting with this 20 amp output. That would be a very revealing graph for this discussion. I don't know how to make such a graph...

dj

Here's some data I collected last year. The batteries were 2 Group 31 Firefly batteries with a charge acceptance rate of .4C. The alternator is a Balmar 165a controlled by a 618 regulator with the field current limited and a temp limit of 100°C. Over the course of an hour the SOC was raised 30 percentage points. At 20 minutes you can see the acceptance rate begin to decline, over the hour it declined from .36C too .26C as the internal resistance increased. Like wise voltage was increasing and approaching the absorption voltage of 14.4. After an hour I decided to stop wasting diesel and let the sun take over. It had been a couple of very overcast days on anchor in December.

 

[dLj]

Here's some data I collected last year. The batteries were 2 Group 31 Firefly batteries with a charge acceptance rate of .4C. The alternator is a Balmar 165a controlled by a 618 regulator with the field current limited and a temp limit of 100°C. Over the course of an hour the SOC was raised 30 percentage points. At 20 minutes you can see the acceptance rate begin to decline, over the hour it declined from .36C too .26C as the internal resistance increased. Like wise voltage was increasing and approaching the absorption voltage of 14.4. After an hour I decided to stop wasting diesel and let the sun take over. It had been a couple of very overcast days on anchor in December.

View attachment 212624

Nice table - I also read through Rods article you posted the link to, while my question was not answered, it is a very interesting write-up!

The exact reason I've gone away from lead-acid chemistry is the difficulty (time/energy) to get back to 100% fully charged. Fighting with sulfation is a never ending battle and actually getting a fully charged and then equalized battery is very difficult to do as a live-a-board. Lithium ion batteries do not have this problem.

But I digress from the OP's original query.

His question was has anyone put on a dual fuel generator as a backup power source. To answer that, yes I have.

I put the generator on my rear platform and hook it directly into my shore power plug on the outside of the boat every time I am going to use it. I would not have considered hooking up the 12v output (mine doesn't have one, but wouldn't consider using it unless it matched or exceeded the power output of the AC side).

I would not use propane for this, I would use gasoline. I like to keep my propane installation as simple and small as possible - it runs only my stove.

I store the generator inside my boat when not in use and take it out and tie it onto my rear platform for use. Three reasons for this - noise, to avoid theft and to keep the unit exposed to the sea environment as little as possible. Time will tell if I like this set-up or not. I will use the generator for backup charging of my batteries and if I want to use my heat pump or electric hot water element. The heat pump and hot water I won't run off my inverter, they are too close to maximum capacity as single units, and together - they would destroy my inverter... Not a good thing... My hot water tank is dual heated, engine or electric. My heat pump - only runs off shore power (generator).

dj

 

[jssailem]

12V output of a generator that only gives 20 amps of output. That's what I'm referring to as trickle charging.

Also relevant in this statement is the 20 amp out put is maximum ouput. These systems are not efficient. Like alternators that claim 75 Amps typically produce 50% or less of that output when measured at the battery point of input.

 

[Benny17441]

Our experience is the following: We first got a Honda 3000 which had electric start and produced the power to tun the A/C unit. It was too big, heavy and had no weather proofing, so we downsized to a Portable Honda 2000. The smaller Honda was shorter in power, run time but had excellent weather proofing and was easily carried, stored and set up on deck. Our main focus is the capacity to run the A/C which we attained by installing a Soft Start Capacitor to provide the needed surge at compressor start up. Our normal usage is to run refrigerator on the batteries while underway and as soon as we get to an anchorage we fire up the generator to recharge batteries. With just the charging load and the refrigerator the Honda fuel consumption and exhaust noise are low. Latter on in the evening well turn on the AC. With the A/C on the run time is about 5 hours so to avoid the in the middle of the night feeding we hooked up an external 3.5 Gallon tank which extended the range to around 17 hours. We wake up in the morning with fully charged batteries and ready to do it all over again. The refrigerator runs off the batteries so it does not directly affect the loads on the generator. The unit is capable of running the A/C and battery charger simultaneously. We have been in major rainstorms and the honda generator keeps on ticking. That generator has allowed us to have a small battery bank of 220 Ah which is more than we need for a day as long as we can recharge. The advantage of a small generator is that it is better and more economical to run and replace the generator than the large, expensive inboard diesel. Don't know if by running it with propane it will have the power to start the A/C unit. It would indeed be a convenience to run with propane as carburetors get gummed up and having gasoline on the boat requires an extra degree of care.