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Old 03-16-2018, 11:06 AM   #1
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Generator load bank

When charging the house bank at anchor, our 8Kw generator is mostly just powering the battery charger, so very little load there. I've been using an electric heater to help provide additional load. It works pretty good but wondering if I there is a "load bank" device that I could hard wire into the 120V system and simply switch on/off? Somewhere in the range of 10-12 amps would be ideal. Any ideas?
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Old 03-16-2018, 11:56 AM   #2
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When charging the house bank at anchor, our 8Kw generator is mostly just powering the battery charger, so very little load there. I've been using an electric heater to help provide additional load. It works pretty good but wondering if I there is a "load bank" device that I could hard wire into the 120V system and simply switch on/off? Somewhere in the range of 10-12 amps would be ideal. Any ideas?

Two questions
  • How big is your inverter charger
  • How large a house bank
We use our 125 amp inverter charger, washer, dryer, water heater, cooking, electric grill, coffee pot, reverse cycle heaters and/or hair drying as our load bank. So long as we hit +50% load on a 12.5 kW unit for about 20 minutes a day (preferably AM) we are happy with lower amps for an hour or so afterwards.

We can get to near 100% load on occasion so do need to watch meters.
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Old 03-16-2018, 12:00 PM   #3
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There are load banks. Google AC load banks and you will find lots of suppliers. But it would have to be very well ventilated. Here are some suggestions to reduce genset running time and keep it better loaded while charging:

Use a larger charger. You may have to increase your house bank size to stay within the recommended 25% charging rate of your battery bank capacity, but a larger charger, at least 100 amp will pull about 15A AC while in its bulk and absorption phases.

I always turn on the water heater as the charging current drops off. This will add about 1,500 watts for about 45 minutes until it trips off.

Then shut your genset down when the charging current drops off to less than 50 amps and install solar panels to finish topping off the battery bank.

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Old 03-16-2018, 12:02 PM   #4
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10-12 amps at 120V is 1200 watts of energy to dissipate somewhere (physics). So you'd essentially just have another heater ---- unless it was some other type of energy consuming device generating motion, etc.
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Old 03-16-2018, 12:27 PM   #5
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I built a seachest of sorts for raw water distribution and incorporated two 1,000 watt stainless steel immersion heating elements. Wired one on each leg of the 220v breaker panel for a pretty slick water cooled dummy load. Basically you could add 1 or 2 KWs of load and the heat would be absorbed by the generator raw water system. Added water heater over temp switches to protect the system from operator error. Even put a very large anode in the box to prevent electrolysis. In testing, it worked extremely well.

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Sadly, the there was an electrolysis problem with the heating element where the tube was soldered into the fittings. Discovered this when pulling one of the elements to reseal a small drip. The 2 elements solder joints were badly eaten along with the anode after 6 months. I then reconsidered all the things that could possibly go wrong with 120vac in the boats raw water system, and removed the elements. Sometimes it's better to accept defeat after the first volley.

Currently have a small electric heater in the engine room and run the exhaust fan when it's on.

The other option is to run the block heater on the main engine. The local volunteer fire department in Delaware leaves them on 24/7 on the fire trucks, so the engines are mostly up to temperature when they turn the key and go (they also have umbilical air lines to maintain pressure for the air brakes).

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Old 03-17-2018, 05:58 AM   #6
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Plan B might be a 2000w Honda humming away on the back deck.
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Old 03-17-2018, 07:34 AM   #7
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Sea Life had a terribly oversized 12kw when purchased (propane cooking). It was replaced with a 6kw. I also added a second inverter/charger. Now with watermaker, water heater, holding plate compressor, and chargers, it is not too hard to keep the gen properly loaded.

Maybe a 120v watermaker, depending on your current/future cruising needs? Second charger also nice if battery bank is large enough, and you get redundancy if it is ever needed. Sell 8kw and replace with smaller?

I feel most gen sets are oversized for a typical cruising boat. Not many want to run 3 A/C units 24/7 while cruising. But when was the last time you heard of someone’s generator having to be replaced because they under loaded it? So unless you plan on a lot of years and hours on the generator, probably easier to not worry.
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Old 03-17-2018, 07:54 AM   #8
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But when was the last time you heard of someone’s generator having to be replaced because they under loaded it? So unless you plan on a lot of years and hours on the generator, probably easier to not worry.
This. As long as it has some nominal load on it, an 8kw would be fine, my 20kw Onan certainly was.
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Old 03-17-2018, 11:05 AM   #9
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Generator load bank

Thanks all for the feed back...but can't use water heater because the Kabola furnace/boiler keeps water too hot for it to turn on; with 300 gals. water no need for watermaker; PNW so no aircon...Probably best to just keep using the portable electric heater (easy on/off). Though I do like suggestion to add another battery charger for quicker bulk charging the 1200 A/h house bank.
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Old 03-18-2018, 09:18 AM   #10
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I just seems so counter productive to intentionally generate a bunch of waste heat and extra fuel burn. I'd add more charge capacity, and even more battery capacity. At least you get a benefit from those. And otherwise just run the generator as needed. It's there to serve you, not the other way around. The worst that will happen is you will need to change out the exhaust elbow sooner than otherwise
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Old 03-18-2018, 11:49 AM   #11
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What kind of gennie is it? I have a 8kW Onan (Kubota engine) in my shop that acts as my hurricane gennie for the shop and house. It has a lot of hours on it as I am in hurricane central at the bitter end of the power line. Lose power for days and days. I run it continuous for fridge and lights and often the load is very low. Sometimes don't need AC or heat. Does not seem to have suffered at all, good compression, no oil use, burns clean.

In my boat experience I don't think I have ever seen a Kubota powered gennie suffer from light load running.

To the OP, if you want to load it up get some 1.5kW cube heaters and turn off your diesel furnace. A couple cubes and your water heater will get you 4.5kW of load.
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Old 03-18-2018, 12:04 PM   #12
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NW Boater

Sounds like your diesel furnace is controlling the genset. Assuming you have an electric water heater, valve or re-plumb it so if you want you can bypass it out of the diesel furnace loop. Then the water heater becomes your heat sink.

Our vessel is set up this way; we found we seldom have a need for the diesel furnace to heat the water. Our water is normally heated via electric or when the main engine coolant circuit valves to the heater are opened. We also can heat the diesel furnace coolant via engine takeoffs or with a separate 1500 watt electric furnace coolant heater.
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Old 03-18-2018, 12:30 PM   #13
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Thanks all for the feed back...but can't use water heater because the Kabola furnace/boiler keeps water too hot for it to turn on; with 300 gals. water no need for watermaker; PNW so no aircon...Probably best to just keep using the portable electric heater (easy on/off). Though I do like suggestion to add another battery charger for quicker bulk charging the 1200 A/h house bank.


You have a very large battery bank (which is nice) but if your charger will only charge at 125 amps max, that is probably a pretty low charge rate. I have a MagnaSine MS2812 inverter/charger. It maxes out at 125 amps which is about 25 amps under what would be ideal for my 780 AH agm battery bank.

If you could add a second charger (I have no idea how you would do that) then it would reduce your bulk absorb time significantly. I donít think it would affect the absorb charge time however.

We have a 6KW genset so our issue isnít as large as yours, but when we run the genset we try to add power to keep the genset loaded. We use; electric heaters, 120/12v fridge, water heater, dehumidifiers (we have 3 Peltier dehumidifiers on board), oil pan heater, AC stereo, and phone and tablet chargers to keep the load up. For us the issue is during the absorb charge phase.

In the summer when even the mornings are warm, we donít run the electric heaters but do our best with the rest.
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Old 03-24-2018, 11:11 AM   #14
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NW Boater

Sounds like your diesel furnace is controlling the genset. Assuming you have an electric water heater, valve or re-plumb it so if you want you can bypass it out of the diesel furnace loop. Then the water heater becomes your heat sink.

Sunchaser, I like your suggestion to take the HWH out of the hydronic (Kabola) loop, allowing the dual electric coils to create a load, but honestly, the small portable electric heater does the same thing...and no need to turn valves or flip switches.
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Old 03-24-2018, 11:22 AM   #15
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If you could add a second charger (I have no idea how you would do that) then it would reduce your bulk absorb time significantly. I donít think it would affect the absorb charge time however.

Dhays, a few months ago I added a second charger. It charges the stern thruster batteries and adds 75 amps to the house bank, for a combined total of about 200 amps. Haven't had to recharge with the generator yet but do expect these extra amps will shorten bulk charging phase. With a 1200 a/h bank I could still add another 75-100 amp charger!
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Old 03-24-2018, 11:42 AM   #16
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To break in my new Kubota powered 8Kw Phasor I used both air conditioning units with the windows open plus two cube electric heaters (12 amp) from Dollar General $16 each. Everything else onboard cycles off too soon to be useful more than an hour. Make sure that you plug the heaters into different branch circuits. If you have a receptacle on the FB it’s perfect for one heater.
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Old 03-24-2018, 11:49 AM   #17
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I don't think load banking a modern gen set based on a light weight high speed diesel is important. As others have said, if you are concerned run a few space heaters and call it good.

Here's my story of two identical gen sets, one lightly loaded, the other not.

Trawler Forum - View Single Post - The Mythical 20,000 Hour Engine??
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Old 03-24-2018, 01:01 PM   #18
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I'm with TwistedTree. It seems so wasteful to generate electricity for no reason. I guess my parents yelled at me so often for leaving the fridge door open too long, or not turning lights off when I left the room, that I'd have a hard time with paying to create electricity that I didn't need. Could you run the genny while you're cooking dinner ? Or maybe an ice maker that you keep a cooler full with ?

It would require a lot of guesswork, but might be interesting to compare the operating costs of a low load vs adequate load generator. If a generator is going to run for 5000 hours, and you are adding 2 dollars per hour in fuel burn and maint., if you can repair it for $10k you might be better running it at the low load.
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Old 03-24-2018, 02:18 PM   #19
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Part of the issue may be as simple as do you plan to follow the manufacturer and dealers recommendation. Pretty sure my Onan owners manual has a minimum load recommendation. I know my dealer / service center does.

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Old 03-24-2018, 02:20 PM   #20
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The following probably isn't relevant to the discussion of load banks, but if you got this far, you might be interested in the following study that Victron did on a dozen or so marine gensets. I suspect that the study was done to promote hybrid generators which use a battery bank and inverter to keep the genset loaded and reduce running time.

Here is the study- https://www.victronenergy.com/upload...7-jan-2008.pdf

Anyway the study has lots of interesting (well at least to us gearheads) data. The most interesting is the absolute efficiency chart: energy (diesel) in vs energy (electric power) out. For a typical 7KW generator it starts at about 12% for 1 KW produced and peaks at about 25% at 5 KW. A smaller Fischer Panda 4KW generator starts at 15% at 1KW and peaks at 24% at 3KW.

The conclusion is keeping the load at 50% or more of is best for efficiency. Not coincedently that is where you should run your genset to avoid low load problems.

With regard to the last statement, I know that many posters here have no problem with low loading. But I am reminded of a conversation with the manager of Bayshore Marine in Annapolis after he installed a new Northern Lights genset in our boat. He said that they have a good business overhauling gensets that spend the winter in the Caribbean running the genset 24/7. At night with the light cycling A/C producing little load it glazes the cylinders and causes oil consumption. The fix is easy- pull the head and piston and hone the cylinder, but costs a bunch for the removal, disassembly and reinstallation.

His advice was to keep it loaded to 50% or better.

Where is all that efficiency losse going- exhaust heat, conduction/radiation from the block, cooling water losses and generator losses. They all add up. As I recall from my college thermo class the Otto cycle (the one diesels use) has a theoretical maximum efficiency of about 40%. Very low speed marine diesels approach that maximum.

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