how do i do this?

Fulthrotl

~Autocorrect is My Worst Enema.~
i just got a 3.5KW 120 volt insta hot water heater for warm showers while overlanding.

i have a 3 KW full wave inverter in the jeep. 6 kw peak load.


i've not smoke tested it yet, but if the water heater overloads the inverter, is there any
sort of thing i can use as a rheostat to trim the power consumption so it'll run on my inverter?
something like a variac, but it'll need to handle 30 amps.

i have an alternator that will produce 3kw at idle, so it won't suck the batteries dry.

the water heater requires 28 amps, and the inverter breaker is supposed to be 32 amps,
so it's close.

thanks in advance.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
211116-2331 EST

Fulthrotl:

If we assume the heater is a simple resistor, then current will be proportional to voltage. Thus, lowering voltage will lower current.

So if you have a Variac of adequate current capability, then use the Variac to test what voltage you want to apply to the heater.

To get down to 3 kW you need to drop voltage by the ratio sq-root of 3/3.5 = 0.925 or from 120 to 111 V. I would be more inclined to go to 2.5 kW or voltage from 120 down to 102 V.

Variacs are quite expensive so I would use a 120 to 18 V 30 A, 500 or 1000 VA secondary transformer to do the step down.

.
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
i just got a 3.5KW 120 volt insta hot water heater for warm showers while overlanding.

i have a 3 KW full wave inverter in the jeep. 6 kw peak load.


i've not smoke tested it yet, but if the water heater overloads the inverter, is there any
sort of thing i can use as a rheostat to trim the power consumption so it'll run on my inverter?
something like a variac, but it'll need to handle 30 amps.

i have an alternator that will produce 3kw at idle, so it won't suck the batteries dry.

the water heater requires 28 amps, and the inverter breaker is supposed to be 32 amps,
so it's close.

thanks in advance.

You could use a buck-boost transformer to reduce the voltage. Basically, it's an autotransformer like a variac, but it's not variable. ;)

This one would reduce the power to 3.5kW x (110/121)2 ≅ 2.9kW but others are available:
https://www.larsonelectronics.com/p...121v-primary-110v-secondary-32-1-amps-50-60hz

I've just seen that gar has posted a similar thought.
 

Fulthrotl

~Autocorrect is My Worst Enema.~
Any chance you can just configure your inverter to output 100V instead of 120V?

Cheers, Wayne
there is other stuff running on it that needs a proper voltage of 120 volts.
microwave, induction cooktop, and various electronic widgets.

the buck/boost mentioned above is the logical solution, but it's a brick,
and i was wondering if there was something else that might work that was
adjustable that i hadn't a clue existed. some spiffy doodle thing. i suspect
that there is not going to be a spiffy doodle coming to the rescue this time.

so, we have a brick. it's not that bad, it's six pounds. i'll call up tech support
on the heater in the morning. they actually had a pretty robust owners manual,
and see what i can do without killing it.

if the jeep is idling, it's producing about 14.4 at the terminals of the inverter....
i'll hook it up in the morning, with the fluke power meter measuring, and see
what happens.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
You will need to hack things somewhere.

The controls for the heater need 120V. So you can't simply drop the input voltage and expect things to work.

On the other hand, the heater almost certainly includes something like an SCR power control to regulate the amount of heat applied and the output temperature.

If you simply reduce the water flow I bet the power consumption goes down.

You will need to see if this plays nice with the inverter, the power regulation might be sub cycle like a light dimmer (creating lots of harmonics) or it might be longer period (creating frequent pulses of full power)

Jon
 

Fulthrotl

~Autocorrect is My Worst Enema.~
You will need to hack things somewhere.

The controls for the heater need 120V. So you can't simply drop the input voltage and expect things to work.

On the other hand, the heater almost certainly includes something like an SCR power control to regulate the amount of heat applied and the output temperature.

If you simply reduce the water flow I bet the power consumption goes down.

You will need to see if this plays nice with the inverter, the power regulation might be sub cycle like a light dimmer (creating lots of harmonics) or it might be longer period (creating frequent pulses of full power)

Jon
well, all the parts are ordered and in process.

reducing the water flow is my first strategy.
it's designed for a 55 degree rise at 1 GPM.
i'll probably limit it to half a GPM. it showed up
last night, and i'll pull it apart and see how it works.
hopefully it doesn't just switch on and off at full power
to regulate.

the goal is to make an expedition grade overland
vehicle that can be converted back to real world stuff
when not crossing the alps with hannibal.

i'm using zarges aluminum cases for everything.
one case for food
one case for microwave and induction cooktop
one case for the porta potti and ancillary stuff.
one case for water purification and cooking stuff.
one case for random camping stuff

the things all nest together, and the bottom one
locks into a receiver. so everything can be removed in five minutes,
and leave the jeep empty for other chores. the refer sits on a slide
and can be set out.

the overlanding thing has gone nuts since the covid thing, when
everyone figured out what i knew 40 years ago, that getting away
from all of y'all has merit. you can't get an awful lot of this stuff,
asi it's all sitting in containers off the port of long beach, waiting
forever for delivery.

the roof top tent i wanted i can see from my house almost, in one
of those container ships. it won't be here till first of feb. i found a
outfitter in salt lake city that has awesome stuff, horribly priced.
but they have everything. i was in SLC a week ago, getting stuff
bolted onto the jeep. there is a nice tent, made in south africa.
it's odd. some of the best overlanding stuff available anywhere
is made in south africa. they know how do overland travel there,
it seems.

1637087484114.png
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
well, all the parts are ordered and in process.

reducing the water flow is my first strategy.
it's designed for a 55 degree rise at 1 GPM.
i'll probably limit it to half a GPM. it showed up
last night, and i'll pull it apart and see how it works.
hopefully it doesn't just switch on and off at full power
to regulate.

the goal is to make an expedition grade overland
vehicle that can be converted back to real world stuff
when not crossing the alps with hannibal.

i'm using zarges aluminum cases for everything.
one case for food
one case for microwave and induction cooktop
one case for the porta potti and ancillary stuff.
one case for water purification and cooking stuff.
one case for random camping stuff

the things all nest together, and the bottom one
locks into a receiver. so everything can be removed in five minutes,
and leave the jeep empty for other chores. the refer sits on a slide
and can be set out.

the overlanding thing has gone nuts since the covid thing, when
everyone figured out what i knew 40 years ago, that getting away
from all of y'all has merit. you can't get an awful lot of this stuff,
asi it's all sitting in containers off the port of long beach, waiting
forever for delivery.

the roof top tent i wanted i can see from my house almost, in one
of those container ships. it won't be here till first of feb. i found a
outfitter in salt lake city that has awesome stuff, horribly priced.
but they have everything. i was in SLC a week ago, getting stuff
bolted onto the jeep. there is a nice tent, made in south africa.
it's odd. some of the best overlanding stuff available anywhere
is made in south africa
. they know how do overland travel there,
it seems.

View attachment 2558401
Not odd at all, that's "Safari Central", and has been for over 100 years. People figure this stuff out over that stretch.
 

drcampbell

Senior Member
Location
The Motor City, Michigan USA
Occupation
Engineer
If you're running an engine, you're creating and throwing away a whole lot of heat. Why not use some of that waste heat for heating water, instead of electricity?
03.-Basics-of-Shell-Tube-Heat-Exchangers.jpeg

... i have an alternator that will produce 3kw at idle ...
OK, then. That's what, 400 amps @ 5000 rev/min?

... it's producing about 14.4 at the terminals of the inverter. ...
It should be regulated to provide 14.4 volts (give or take, to accommodate changing temperatures) at the battery terminals. Voltage drop is very significant in automotive wiring. See "remote sense" for further details.
 

Fulthrotl

~Autocorrect is My Worst Enema.~
If you're running an engine, you're creating and throwing away a whole lot of heat. Why not use some of that waste heat for heating water, instead of electricity?
View attachment 2558403


OK, then. That's what, 400 amps @ 5000 rev/min?


It should be regulated to provide 14.4 volts (give or take, to accommodate changing temperatures) at the battery terminals. Voltage drop is very significant in automotive wiring. See "remote sense" for further details.
yep. folks do that. where and how i want to store the water makes it a royal pita. i'm putting an aluminum storage box in the back of the jeep with a 15 gallon rotationally molded water tank inside it, nestled in 1/2" urethane. immersed pump. i can drop a 1,500 watt heater in the tank and heat the whole thing to 103 degrees, but then i have a hot tank of water in the back of the jeep. then it's heating up the jeep. that might suck in the summer. i could heat it the last hour or two before camping, and it'll stay hot all night.

i'm gonna try my insta hot first. it'll be my first choice. the 1500 watt unit is second. they are cheap, and if i went that way, i'd use two for 3kw, and heat the tank twice as fast. you can get ones that you can set and they self regulate.

the heat exchanger has the problem of where do you put it on a JL jeep. things are cozy. showers are brief, as there is 15 gallons of water available for everything without a refill. i have a water filter and sterilizer that will do a gallon a minute, so i can refill from anywhere. i've already got two group 25 batteries under the hood, under the jeep, there are two fuel tanks, the aux is larger than the OEM.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
the heat exchanger has the problem of where do you put it on a JL jeep. things are cozy. showers are brief, as there is 15 gallons of water available for everything without a refill.
Put a coil that circulates engine coolant inside the 15 gallon tank.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
Put a coil that circulates engine coolant inside the 15 gallon tank.
I can see bad things happening inside a plastic tank with coils suspended in it. How do you keep the coil from contacting the tank? Any supports are going to act as conductors right to the tank, and if you have a shutoff valve for when you're tooling down the road but forget to close it, misfortune may ensue.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Just a summary: you have a 15 gallon tank of water. You have multiple tanks of gasoline. You are in the desert and you want to hack something to heat water with electricity.

I think you are doing it wrong :) :) :)

I think you need a gasoline powered tankless water heater. Something that looks like a Russian samovar mounted on the back of the vehicle. Extra style points if visible flame occurs during operation.

-Jon
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
Just a summary: you have a 15 gallon tank of water. You have multiple tanks of gasoline. You are in the desert and you want to hack something to heat water with electricity.

I think you are doing it wrong :) :) :)

I think you need a gasoline powered tankless water heater. Something that looks like a Russian samovar mounted on the back of the vehicle. Extra style points if visible flame occurs during operation.

-Jon
Sounds like something you'd see at Burning Man. 😁
 

Fulthrotl

~Autocorrect is My Worst Enema.~
i've got $120 bucks invested in the tankless insta hot.
i can return it to amazon if i'm unhappy, assuming i can find it
in the burnt residue of the jeep. i can use UL listed immersive
1,500 watt heaters to heat the whole tank. not as elegant, but
it'll work. we don't get paid for pretty, we get paid for done.
i'll address that comment shortly.

here is the deal. i have a jeep. it's paid for. the build out is paid for.
i was looking at overlanding trailers to pull behind the jeep.

overkill trailers from bend oregon makes a cool thing with a pull out.
you will spend more on that trailer than i did buying the jeep full retail
in 2018. you will wait an absurdly long time to get it. i'd guess 18 months
or more. you will give them north of $25k deposit to get on the list.

that is asinine. here is why:

earlier this year, i was diagnosed with stage four cancer. in a drastic,
medically unproven therapy, all traces of cancer disappeared in
about 3 weeks. it taught me, and my spouse something.

none of us have a year and a half. eat dessert first. my little jeep will go
where i want to go, and do what i want to do, RTFN. RTFN beats maybe
in a year and a half or so, by a long distance.

"jeep interiors" by goose gear are the gold standard of overlanding, and
are absurdly expensive, built to order with three months lead time, for
$5k ish. nope. i'm taking the rear seats out of the JL, and putting in a
plate goose gear sells as a floor. until it gets here, there is a sheet of plywood
serving as a test floor, so i can shift stuff around until it gets where i want it.

but, i can leave and do what i want to do, next tuesday. everything will be
working by then, and installed. i'll redo it in december when the plate shows up.
that should largely wrap it.

i wanted something that would support two people off the grid for a week.
water, food, heat, shelter, internet. the jeep will do that. the only thing is a
decent water supply. 15 gallons isn't much. i was gonna build a UV-C and
micro carbon filter for water purification, and then discovered a company
in hood river oregon makes a portable one in a small pelican style case.
so anywhere i've got water is good, unless it's contaminated by heavy metals.

the internet as i'm still doing lighting certifications for select customers, having dumped the bozos.

so i need an internet. i have a couple dozen good customers, and that is enough.
jill's last day is Dec. 10. her VP was on the phone yesterday hammering her
to please say on as a consultant. nope. we have had some long talks about what
is important to us. i dumped the three least desirable customers, and kept the rest.

back to the jeep. all the overlanding stuff can be removed from the jeep
in under 10 minutes, leaving the entire back of the jeep available for carrying bulky
stuff. it can be cleaned, prepped, and loaded back in the jeep in the same 10 minutes,
and off we go.

tuesday, we are turning right at barstow, left at kelbaker road, and taking the 1880s
government trail across the mojave preserve, then thru death valley, and saline valley,
and alabama hills, coming out on 395 sometime the following week.

shakedown run. it's too late this year to do the trans america trail, but i'd like to do it in
late spring. west coast to philly, not on pavement.

canada's border is opening back up. i want to do yukon, and northern lights. left turn at
philly.

i'll need lots of hot water.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
i've got $120 bucks invested in the tankless insta hot.
i can return it to amazon if i'm unhappy, assuming i can find it
in the burnt residue of the jeep. i can use UL listed immersive
1,500 watt heaters to heat the whole tank. not as elegant, but
it'll work. we don't get paid for pretty, we get paid for done.
i'll address that comment shortly.

here is the deal. i have a jeep. it's paid for. the build out is paid for.
i was looking at overlanding trailers to pull behind the jeep.

overkill trailers from bend oregon makes a cool thing with a pull out.
you will spend more on that trailer than i did buying the jeep full retail
in 2018. you will wait an absurdly long time to get it. i'd guess 18 months
or more. you will give them north of $25k deposit to get on the list.

that is asinine. here is why:

earlier this year, i was diagnosed with stage four cancer. in a drastic,
medically unproven therapy, all traces of cancer disappeared in
about 3 weeks. it taught me, and my spouse something.

none of us have a year and a half. eat dessert first. my little jeep will go
where i want to go, and do what i want to do, RTFN. RTFN beats maybe
in a year and a half or so, by a long distance.

"jeep interiors" by goose gear are the gold standard of overlanding, and
are absurdly expensive, built to order with three months lead time, for
$5k ish. nope. i'm taking the rear seats out of the JL, and putting in a
plate goose gear sells as a floor. until it gets here, there is a sheet of plywood
serving as a test floor, so i can shift stuff around until it gets where i want it.

but, i can leave and do what i want to do, next tuesday. everything will be
working by then, and installed. i'll redo it in december when the plate shows up.
that should largely wrap it.

i wanted something that would support two people off the grid for a week.
water, food, heat, shelter, internet. the jeep will do that. the only thing is a
decent water supply. 15 gallons isn't much. i was gonna build a UV-C and
micro carbon filter for water purification, and then discovered a company
in hood river oregon makes a portable one in a small pelican style case.
so anywhere i've got water is good, unless it's contaminated by heavy metals.

the internet as i'm still doing lighting certifications for select customers, having dumped the bozos.

so i need an internet. i have a couple dozen good customers, and that is enough.
jill's last day is Dec. 10. her VP was on the phone yesterday hammering her
to please say on as a consultant. nope. we have had some long talks about what
is important to us. i dumped the three least desirable customers, and kept the rest.

back to the jeep. all the overlanding stuff can be removed from the jeep
in under 10 minutes, leaving the entire back of the jeep available for carrying bulky
stuff. it can be cleaned, prepped, and loaded back in the jeep in the same 10 minutes,
and off we go.

tuesday, we are turning right at barstow, left at kelbaker road, and taking the 1880s
government trail across the mojave preserve, then thru death valley, and saline valley,
and alabama hills, coming out on 395 sometime the following week.

shakedown run. it's too late this year to do the trans america trail, but i'd like to do it in
late spring. west coast to philly, not on pavement.

canada's border is opening back up. i want to do yukon, and northern lights. left turn at
philly.

i'll need lots of hot water.
On desserts. When I was in grammar school, I had a classmate who would always eat dessert first at lunch. We made fun of him. Now, I think he was smarter than the rest of us. We were assholes. Sorry, Brian. That doesn't really cover it, but sorry anyway.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
i've got $120 bucks invested in the tankless insta hot.
i can return it to amazon if i'm unhappy, assuming i can find it
in the burnt residue of the jeep. i can use UL listed immersive
1,500 watt heaters to heat the whole tank. not as elegant, but
it'll work. we don't get paid for pretty, we get paid for done.
i'll address that comment shortly.

here is the deal. i have a jeep. it's paid for. the build out is paid for.
i was looking at overlanding trailers to pull behind the jeep.

overkill trailers from bend oregon makes a cool thing with a pull out.
you will spend more on that trailer than i did buying the jeep full retail
in 2018. you will wait an absurdly long time to get it. i'd guess 18 months
or more. you will give them north of $25k deposit to get on the list.

that is asinine. here is why:

earlier this year, i was diagnosed with stage four cancer. in a drastic,
medically unproven therapy, all traces of cancer disappeared in
about 3 weeks. it taught me, and my spouse something.

none of us have a year and a half. eat dessert first. my little jeep will go
where i want to go, and do what i want to do, RTFN. RTFN beats maybe
in a year and a half or so, by a long distance.

"jeep interiors" by goose gear are the gold standard of overlanding, and
are absurdly expensive, built to order with three months lead time, for
$5k ish. nope. i'm taking the rear seats out of the JL, and putting in a
plate goose gear sells as a floor. until it gets here, there is a sheet of plywood
serving as a test floor, so i can shift stuff around until it gets where i want it.

but, i can leave and do what i want to do, next tuesday. everything will be
working by then, and installed. i'll redo it in december when the plate shows up.
that should largely wrap it.

i wanted something that would support two people off the grid for a week.
water, food, heat, shelter, internet. the jeep will do that. the only thing is a
decent water supply. 15 gallons isn't much. i was gonna build a UV-C and
micro carbon filter for water purification, and then discovered a company
in hood river oregon makes a portable one in a small pelican style case.
so anywhere i've got water is good, unless it's contaminated by heavy metals.

the internet as i'm still doing lighting certifications for select customers, having dumped the bozos.

so i need an internet. i have a couple dozen good customers, and that is enough.
jill's last day is Dec. 10. her VP was on the phone yesterday hammering her
to please say on as a consultant. nope. we have had some long talks about what
is important to us. i dumped the three least desirable customers, and kept the rest.

back to the jeep. all the overlanding stuff can be removed from the jeep
in under 10 minutes, leaving the entire back of the jeep available for carrying bulky
stuff. it can be cleaned, prepped, and loaded back in the jeep in the same 10 minutes,
and off we go.

tuesday, we are turning right at barstow, left at kelbaker road, and taking the 1880s
government trail across the mojave preserve, then thru death valley, and saline valley,
and alabama hills, coming out on 395 sometime the following week.

shakedown run. it's too late this year to do the trans america trail, but i'd like to do it in
late spring. west coast to philly, not on pavement.

canada's border is opening back up. i want to do yukon, and northern lights. left turn at
philly.

i'll need lots of hot water.
That would be awesome. Never knew a trail that long existed.
Im googling it now…
 

Fulthrotl

~Autocorrect is My Worst Enema.~
That would be awesome. Never knew a trail that long existed.
Im googling it now…
it's the TAT. it started as one trail, now it's going everywhere.
the guy who maintains the thing and does it every year does it in a
2wd tacoma. there are lots more difficult trials, but this one catches
the flavor of america. i've been on parts of it in the southwest... it's a good
trek.
this was shot 4th of july weekend with an esteemed member of this forum,
as we headed to telluride, because, well, why not?

2021-11-17_19-59-37.jpg
 
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