Thought exercise with possible real-world generator application

If you don't want to read the whole thing... I'm looking to make a very small, very quiet generator.

In my very preliminary thoughts on converting Candy Van into a capable off-road/boondock camper, I've been giving thought to luxury.  Normally I pitch a tent and my idea of entertainment is a battery powered light and a Stuart Woods novel.  I want to take it up a tiny notch to *gasp* electricity.

Here is what I know I'll be doing:  2/0 cable to the back to mount a deep cycle battery/inverter.  There will be a 200A solenoid between the two batteries that isolates the rear battery when stopped so I can abuse the coach battery and still be able to start the van, but it will also charge the coach battery after starting up.  I did some maths on potential load and I'm concerned that the number of wH I use will require enough battery real estate to be icky, and also that is asking a lot from an OEM alternator to constantly provide that kind of amperage on a regular basis.

So I need some way to supplement juice - something to at least partially replenish the coach battery as I use it.  I know the answer is solar, but that won't work for a few reasons:

• I need supplemental juice when the vehicle is off/camping, which means night time.  During the day when solar is needed, I have the alternator to replenish juice.
• The entire roof will be covered with a platform that hauls cargo for camping and hauls lumber when not vacationing.
• Many of the places I go are densely-packed woods where adequate light isn't great

In thinking of a generator, two things come to mind.  1) nothing is more annoying when you're boondocking and a 30' class A pulls in and fires up their big Onan 10kw generator so they can completely disturb the peace you worked so hard to find.  I don't want to be that guy.  2) Even one of the small, super-quiet Hondas is too loud and too big for my needs.

List of amenities I've though of so far:

• mini fridge, 100w x 24h (running half the time) = 1200wh or 100Ah
• 17" LCD/LED tv, worst case 20w for 4 hours = 80wh or 7Ah
• possible external speakers for TV and music, 30w for 4 hours = 120wh or 10Ah
• Lighting is negligible.  The LEDs I have in the domes are 0.12A, so just over 1w, but let's say 1Ah
• DVD player.  Worst case 20w for 4 hours = 80wh or 7Ah.
• cooling fan for the window = 10w for 10h = 100wh or 8Ah
• Inverter will consume/waste some on its own but haven't researched that yet.  Estimate 20w for 12h= 240wh = 20Ah

I get a potential total Ah of somewhere around 150-200Ah if I just don't care and consume like a glamper.  Any given maximum load at one point should be around 300w (I'm thinking fridge startup wattage included)  which from the 12v source sounds like about 25A peak.

So the way I see it, most deep cycle batteries in normal sizes are somewhere around 75-100Ah.  The monster H8 battery I have I think is 90Ah.  So at best, I think the battery would last 3-4 hours with that load, and certainly not last all night with the fridge.

I also have a nice, reman 20A alternator in a box.  Assuming it puts out a nice 14.4v, that's right around 300w.  300w translates into about 1/2 hp.  Given losses to friction, heat, and other wastes....

Could a guy find a nice, quiet 1-2 hp gasoline engine and hook it up to the alternator for a cute little supplemental charging generator?  Also possible to step up to a 40A alternator and 3hp, but the obvious/common 3hp engines out there are not in any way quiet.

Also... check my math.  Math and I go together like Lamb and Tunafish.

Thoughts on a quiet 1-2 hp power maker?  I'm open to other fuels, but gasoline means I can just use my existing jerry can or tap into the factory fuel line.

Mkm and dad have the red-cased harbor freight generator. The thing is WAY quieter than any other small engine ive ever heard. Its quite amazing, really. It sounds like my mazda idling, and i don't mean the miata!

No help on roll your own, but maybe you don't have to. 

Why fight mental health?  Buy a tiny little Honda lunchbox generator and call it done.

I know, it's not free...

Well, according to current thinking, all you have to do is wish there were no losses, and pretend it will work, and then everything will be fine

I personally have never heard any stand alone engine be very quiet; the 1000W Honda inverter gen, is about the quietest think I can think of. Any engine smaller, is prolly going to end up just as loud, I think.
Hey, just hook an electric motor to the alternator, run part of your output back to the motor, and your all set!  Or a hand held solar panel... solar fixes everything, doesn't it?All you have to do is want it too...

I think more batteries are going to be your only solution, unfortunately, and charge them when you can without disturbing the peace. 

Did you figure your wh at 120v or 12v? That makes a big difference if you are running 120v appliances on an inverter. 

A 120-volt mini-fridge that pulls 100 watts at 120 volts, pulls 1000 watts at 12 volts by the time you run it through the inverter. 

In reply to Streetwiseguy :

I could.  Part of the goal is to simplify.  If I have a 12v system with one inverter, then the fridge can operate seamlessly with either the engine running, on battery, or with a 12v generator.  If I use a 120v generator, I'm either unplugging and replugging the 120v appliances, or I use the generator to power a battery charger.  Seems overly complex to go AC-DC-AC inside the generator, then 120vAC - 12vDC - 120vAC inside the van.  I'm also thinking of cubic feet of space.  The generator I want to make would tuck up under a frame rail and could be on-demand.  A suitcase would have to run all night supplying way more potential than I need, and also represent a storage conundrum.

Imagine waking up in the middle of the forest 10 miles from civilization ready for a bird watching hike... and turning off the generator that just spent the last 12 hours making sure there were no birds in a 1/2 mile radius.

I realize I'm trying to re-invent the wheel, and it may not be possible, but I'd like to at least brainstorm it.

Suitcase generator is still too loud, and it's easily 5-6 times more than I need.

What about a powermaster 200amp alternator? Maybe add a second one like the car stereo guys do?

A Honda 2000eu is about 53db at 25% load. That's going to be substantially quieter than just about any engine you can buy. I have read that the WEN inverter generator is even quieter at 49db. Half as loud as the Honda.

Toyman01 + Sized and said:

Did you figure your wh at 120v or 12v? That makes a big difference if you are running 120v appliances on an inverter. 

A 120-volt mini-fridge that pulls 100 watts at 120 volts, pulls 1000 watts at 12 volts by the time you run it through the inverter. 

 

I calculated watts period.  A 120w appliance is 120w.  It's not the watts that change, it's the amps that change.  Running 120w on 120v is 1 amp.  Running it on 12v is 10 amps.  So I calculated all the wh through to the source and converted it to amps at 12v.  Each step I rounded up for losses.  I came up with 180w if I'm running everything, but I rounded up to 300w for fridge startup, inverter losses, etc.  From there I just converted to the amps required to generate 300w at 12v

Dusterbd13-michael (Forum Supporter) said:

What about a powermaster 200amp alternator? Maybe add a second one like the car stereo guys do?

The van already has a 145A alternator.

And I learned the hard way to never use a hopped-up alternator again for this application.  Fires happen that way.  Any given alternator case design has a max amperage it can carry.  An old 10si from the 60s/70s you're lucky if it will carry 60A.  They make rewound 80A versions for stereos and they're fine because they only supply that amperage for a half-second at a time.  The first time you have a dead battery and get a jump start, that alternator will cook.  It will try to supply 80A for a steady stream and cook itself hardcore.  The 70s/80s 12si case can take 90-100A.  A 13csi case or 14csi case has been known for reliability up to 200A.

The problem still remains, however, that a large battery will exhaust its reserve after 3-4 hours allowing the fridge to get warm.  The other problem also remains that no matter how you slice it, alternators are designed to make their peak amperage only a handful of times in their lifespan.  99% of what they do is make 10 amps to balance out what a running engine takes.  Consistently (daily) asking it to crank out it's peak output dramatically shortens its life.  In fact, if this 145A alternator cooks, I'm strongly considering replacing it with a 105A version of the same alternator so it will cook itself slower.

I put a 125A rewound 12si alternator in my old station wagon for this exact purpose.  Camp at night with a 12v fridge, recharge on the road the next day.  That worked twice.  The third day I lost the alternator and when I lifted the hood, the black paint on the stator plates was on fire, and the charge wire connector had melted and was smoking.  My greasy fingerprints on the alternator case were cooked to gray ash.

It's not increased alternator output I need, it's consistent, small, supplemental power when the engine is off.

03Panther said:

Hey, just hook an electric motor to the alternator, run part of your output back to the motor, and your all set!  

 

When I worked at an equipment rental, I never could have been prepared for the number of people who came in asking for an electric generator instead of gas.  People straight up wanted to generate electricity with electricity.

I can understand people not understanding how it works, but at its most base level, they're asking for an implement that generates electricity in a place where they already have electricity

If only there was a way to harness the incredible power of the sun! 

https://4patriots.com/products/patriot-power-generator-1800?AFID=ACQ_BING_SHP_PPG_Sr-11&utm_campaign=ACQ_BING_SHP_PPG_Sr-11&utm_medium=&utm_term=cid-316475436&utm_content=agid-1341404611737146_adid-&source=cid-316475436_agid-1341404611737146_ad-_target-pla-4587437392192216_network-s_dev-c_placement-&msclkid=f2136b32f9a5183457c60bb1ff801d2d

1988RedT2 said:

If only there was a way to harness the incredible power of the sun! 

during the day, I will be running the engine.  During the night when I'm consuming the power is when I need the supplement to extend the battery life.  I realize my initial post was long, but the reasons that solar are a terrible choice for me are all listed in the first post.

Curtis73 (Forum Supporter) said:

03Panther said:

Hey, just hook an electric motor to the alternator, run part of your output back to the motor, and your all set!  

 

When I worked at an equipment rental, I never could have been prepared for the number of people who came in asking for an electric generator instead of gas.  People straight up wanted to generate electricity with electricity.

I can understand people not understanding how it works, but at its most base level, they're asking for an implement that generates electricity in a place where they already have electricity

Sounds like a modern lithium battery semi-truck APU

On that note, I was thinking you may need to upgrade your battery type. A battery module from an EV's pack would cram a lot of capacity into a small space and would be relatively cheap, this is what my 4x4 mechanic uses for his off-grid energy setup.

(he was using a few of them to run a full household fridge, TV, computer etc, but just one should pack more energy than any lead-acid car battery at a lower weight and volume.)

Toyman01 + Sized and said:

A Honda 2000eu is about 53db at 25% load. That's going to be substantially quieter than just about any engine you can buy. I have read that the WEN inverter generator is even quieter at 49db. Half as loud as the Honda.

I see the point.  It will be hard to find a 1 hp gas engine that is quieter.  I just don't really like the size aspect, nor do I like that it is not proportional to demand.

I'd be looking at a pretty intense electrical system using RV components to integrate multiple AC and DC inputs and being able to output both DC and AC.  My reasoning for keeping it 12v was so that it seamlessly integrated on the charge side and only uses a single inverter on the output side.

Curtis73 (Forum Supporter) said:

Toyman01 + Sized and said:

Did you figure your wh at 120v or 12v? That makes a big difference if you are running 120v appliances on an inverter. 

A 120-volt mini-fridge that pulls 100 watts at 120 volts, pulls 1000 watts at 12 volts by the time you run it through the inverter. 

 

I calculated watts period.  A 120w appliance is 120w.  It's not the watts that change, it's the amps that change.  Running 120w on 120v is 1 amp.  Running it on 12v is 10 amps.  So I calculated all the wh through to the source and converted it to amps at 12v.  Each step I rounded up for losses.  I came up with 180w if I'm running everything, but I rounded up to 300w for fridge startup, inverter losses, etc.  From there I just converted to the amps required to generate 300w at 12v

You are correct. 

Are you trying to supplement the battery or charge it? At 20 amps it will take a lot of hours to charge a 100 ah battery. You might be better off with a larger alternator and engine. More noise but less run time.

Have you considered LiFePO4 batteries? A lot more power density, 80% discharge, and less weight. Not cheap but you could probably run several days without charging. They are available to 300 ah.

You also might consider a 12v fridge/freezer. I have a 54 qt I use for camping and the 100 ah AGM house battery in my XJ will run it for several days without charge. They are better insulated and draw less power than a mini-fridge. 

https://www.harborfreight.com/generators-engines/generators/1400-watt-super-quiet-inverter-generator-with-co-secure-57063.html

At $430 before coupons, there really isnt a reason to do something else for camping to me.  You will likely spend more rolling your own if you arent cobbling together used junkyard parts.  Build a sound enclosure for it and you can achieve quieter as well.  

GameboyRMH said:

Curtis73 (Forum Supporter) said:

03Panther said:

Hey, just hook an electric motor to the alternator, run part of your output back to the motor, and your all set!  

 

When I worked at an equipment rental, I never could have been prepared for the number of people who came in asking for an electric generator instead of gas.  People straight up wanted to generate electricity with electricity.

I can understand people not understanding how it works, but at its most base level, they're asking for an implement that generates electricity in a place where they already have electricity

Sounds like a modern lithium battery semi-truck APU

On that note, I was thinking you may need to upgrade your battery type. A battery module from an EV's pack would cram a lot of capacity into a small space and would be relatively cheap, this is what my 4x4 mechanic uses for his off-grid energy setup.

(he was using a few of them to run a full household fridge, TV, computer etc, but just one should pack more energy than any lead-acid car battery at a lower weight and volume.)

Keep talking.  I know so little about alternate battery tech (other than experimenting with 18650s scavenged from laptop batteries and cordless power tools).

The point here is the least amount of hands-on I can get.  I don't want to spend 10% of my vacation monitoring, starting the engine, running a generator, plugging things into different outlets, filling a generator tank, etc.  I want to turn off the engine, watch a movie, turn on the fan, and go to sleep knowing that my fridge will still be cold in the morning.

So from the very rough, estimated math above, if 100Ah will give me 3 hours, I need at least 400Ah to last all night.  Then I can fire up the engine and give it an average 100A, which suggests it would take a long time to recharge while idling a 5.3L V8.

This was my initial motivation for using a smaller, "float" of juice to maintain instead of large capacity that drains and has to be fully recharged.

Toyman01 + Sized and said:

Curtis73 (Forum Supporter) said:

Toyman01 + Sized and said:

Did you figure your wh at 120v or 12v? That makes a big difference if you are running 120v appliances on an inverter. 

A 120-volt mini-fridge that pulls 100 watts at 120 volts, pulls 1000 watts at 12 volts by the time you run it through the inverter. 

 

I calculated watts period.  A 120w appliance is 120w.  It's not the watts that change, it's the amps that change.  Running 120w on 120v is 1 amp.  Running it on 12v is 10 amps.  So I calculated all the wh through to the source and converted it to amps at 12v.  Each step I rounded up for losses.  I came up with 180w if I'm running everything, but I rounded up to 300w for fridge startup, inverter losses, etc.  From there I just converted to the amps required to generate 300w at 12v

You are correct. 

Are you trying to supplement the battery or charge it? At 20 amps it will take a lot of hours to charge a 100 ah battery. You might be better off with a larger alternator and engine. More noise but less run time.

Have you considered LiFePO4 batteries? A lot more power density, 80% discharge, and less weight. Not cheap but you could probably run several days without charging. They are available to 300 ah.

You also might consider a 12v fridge/freezer. I have a 54 qt I use for camping and the 100 ah AGM house battery in my XJ will run it for several days without charge. They are better insulated and draw less power than a mini-fridge. 

 

 

I did consider a 12v fridge, but the modern compressor-style 12v fridges are bloody expensive.  Like 15 times more than a dorm fridge.

The ARB 12v fridges draw about 1Ah which is about 1/4 what a dorm fridge does.  That would remove about 100Ah from the needed capacity which is significant.  Worth it for the $1200 buy-in?  Not sure.

Talk to me more about LiFePO4 stuff.

I'm trying to supplement with a generator that is almost equal to my usage.  I don't need a big thing to run one hour to recharge everything, I'm thinking that if I'm consuming 25A peak, 10A average, if I had the ability to charge 20A, I could pretty much camp indefinitely.  The goal is to spread out a quiet float of available juice instead of drawing down a 400Ah battery and asking an alternator on a V8 to recharge it.  Not only is that a waste of V8 potential and fuel, it's maxing the alternator every single day.

Think of it this way.  Let's say you have a 10A load hooked up to a 100Ah battery.  You get 10 hours.  Now let's say you add a 9A charger to it.  You now get 100 hours.  So, if you use that 10A on the 100Ah battery, then start up the engine/alternator, it will peg to full amperage for at least an hour every morning.  If, instead, you have 9A going in to the system from a small generator, after 10 hours your alternator only has to catch up on 10Ah instead of 100Ah.

That's my thinking behind a 20A generator.  It may not supply enough to power it all, but it's enough to throw some juice back in and extend/reduce load on the alternator.

I have been RVing, mostly boondocking for more than 20 years, and am an EE. There, just to get that out of the way, sorry, just tough sometimes. First off, you won't need 2/0. Can get away with much smaller, I used 4 ga in my recent charge setup for truck with slide in camper. Most of the resistance will be internally with batteries, and if you lose that resistance and go with lithium in the future it could actually put your van alternator in jeopardy or force you into DC/DC controllers which gets spendy fast. 

Look at your loads and the fridge is really the issue. If you do an RV fridge (propane) you are good to go. They are very efficient and work great. Then you don't need a generator at all for a few days camping. Also lets you do an RV heater if you want in the future, so no condensation or lack of oxygen inside. I could go 2 days in pretty cold camping on a single battery keeping the inside of the camper at 65 or so. 

Food for thought. Jcamper

In reply to Jcamper :

Excellent food for thought.  Very thankful to have an EE in the thread.  Propane/evap fridges are great, but they are also huge and have specific venting needs.  There is way more refrigeration proportional to the space.  This is also not an installation.  This is my DD/work/cargo van.  This needs to be a "throw in a mattress and a fridge and hit the road" thing that can completely return to an empty van.  I'm not converting it to a camper, I'll be using it on the weekends/summer and converting back to a regular van for work in between.

Think of it like a slide-in camper.  Slide it in the bed for the weekend, put the jacks down and drive the truck away for work when you're done.  Only in my case it will be a mess kit, a mattress, and a fridge instead of a complete RV.  The van needs to be un-campered and re-campered easily.

No need for heat that I anticipate.  I don't mind camping in a tent in 50 degrees and have done it in 20 degrees.  Suffice it to say, if it's cold enough that I need heat, I could use the Yeti cooler and free up that 100w for a wee heater to take the edge off.

Edit:  But your acknowledgement of the fridge being the issue is a very good point.  There are mini fridges (1.6 cu ft range) that are rated for closer to 50-65w which would help, I more or less tried to find the highest-wattage examples I could so I had headroom.  I was making a worst-case scenario.

Curtis73 (Forum Supporter) said:

Keep talking.  I know so little about alternate battery tech (other than experimenting with 18650s scavenged from laptop batteries and cordless power tools).

So you've got 2 different types you can go for as I see it- Nickel Metal Hydrides, or a lithium architecture. I suppose I could also count Nickel-Iron "Edison" batteries too, but they are honestly so heavy, difficult and specialized the only time I ever saw some for sale were from a railyard powering lights.

NiMH cells can be yanked out of most hybrids and tend to come in nice, consistent packs that need only air cooling thanks to the cell physically not pumping out enough juice (or having anything oxidizing like lithiums) to really start itself on fire. Prius cells I know, are ~201 Volts nominal and about 6.5 Amp hours. Their cells are prismatics, long and thin like an odd book and the whole pack runs close to the length and width of the back seats.

Usingg NiMH would be hard. They're built to be charged off the alternator no problem, but I have NO concept of what Toyota uses for a Delta-V to charge them- the special algorithm that tapers charge to the cell based on internal resistance or something- but I do know aftermarket chargers do exist. I'm also not sure if you can just Yoinky-sploinky the charge electronics out of a Prius and adapt it to the pack itself either; turning the battery into a standalone would be very easy, but charging it would be an exercise. Still tho, they have a cycle lifespan of like ~10 years if you treat them well and NiMH can handle some wild temps. There are Prii running decades on the OG Packs. I know they are also in other hybrids like the Ford Escapes and some others.

Lithium has other problems from NiMH; cost is higher, charging is far easier, Weight is much less, voltage and capacity are far higher. If you use Nickel-Manganese-Cobalt type- the Tesla and tool pack cell, Lithium Ion- It'll be one that can explode if not treated properly and cannot take extreme temps. If you go for the hardier and not nearly-as-explodey Lithium Iron Phosphate, you'll have about 60% the total charge as said NMC cells and less voltage but trade for more than double the lifespan and some of the best temperature resistance known, and also gain far higher discharge rates thanks to that Iron Olivine complex they have.

Used NMC cells can be picked up from wrecked Hybrids and EVs, and it would be pretty easy to make a charger that could plug into the 12v in your car with some kind of voltage step-up (obviously at the cost of efficiency) and it would be something in a metal case with obvious busbars. LiFEPO4, the Phosphates, are a little bit harder- you can still get them in packs, but China is the one nation that really uses them, so if you find some they're typically out of a bus or from a failed startup.

For 400Ah, you're probably looking only at NMC and phosphates unless you find Prius cells on the cheap and a guide to use them out of the car. Some of the phosphate batteries at 400Ah on Amazon are the size of two car batteries end-to-end.

Back to the fridge. How much space do you need? When I'm camping by myself I carry this one. It's 20 liters/21 quarts. It will hold more than enough food for me for 2 days and enough for 2 people if you pack it carefully. It draws 45 watts. Not as efficient as the super expensive 12v fridges but it's also only $200 which is less than the AGM battery in the XJ. Their 50 liter is only $319. Link is HERE.

Curtis73 (Forum Supporter) said:

 the reasons that solar are a terrible choice for me are all listed in the first post.

You just don't want it to badly enough! 

Like people that wanted to electric to electric "generator" (don't get me started on calling a battery pack a "solar generator ") I've literally been told that while trying to explain why... well , you know where the rest of that goes! Way off topic 

I am interested in seeing where legit suggestions go, as I need a rear AC (in a suv that never came with one) for the furry kids, that will run while parked for a few hrs as well  

Getting back to the original question, a small air cooled gas engine is going to be inherently loud.  You could play around with a larger muffler but it will still be noisy.  Some sort of sound attenuating enclosure could be built, but it would have to allow for enough airflow so the engine doesn't overheat.

If you were always camping next to a lake, I suppose a small outboard motor could be used to run the alternator since they're water cooled and relatively quiet.