Anyone using a tankless water heater?

[cygvan]

i think i found what i was looking for....the calculator on the concorde website pointed out what should have been obvious to me...i hadnt come across that one before...

thanks daveb...that little piece of info made it make sense

[daveb]

Try this link also. I just upgraded the link as it had changed in the FAQ's
http://www.windsun.com/Batteries/Battery_FAQ.htm

if you have 600AH of battery, that's huge!

[cygvan]

Originally Posted by daveb

Try this link also. I just upgraded the link as it had changed in the FAQ's
http://www.windsun.com/Batteries/Battery_FAQ.htm

if you have 600AH of battery, that's huge!

600ah is the plan although im working out all the numbers now that i have a little more info...400ah might be ok...

i have a local source of batteries down the street...saves on shipping...

that website is great...i found it when i first started fleshing things out...i plan on buying my kd135's there unless i find them locally as well...im boondocking big time in this van so a small fridge will be on 24/7....everything else will be switched on as needed pretty much in order to conserve...im still wrestling with cooling...heating cooking and hot water i got worked out...

[Kzinti2]

Originally Posted by cygvan

i read that the eemax draws 20a. how does this translate to drawing 200a from batteries? i thought that means it draws 20 amps per hour. if not, how the heck does one figure how much their battery banks are being depleted by ANY device?

The problem comes in thinking about power consumption in terms of Amps (Amperes, which is dependant on voltage) versus thinking in power consumption in Watts. The key formula that illustrates this is:

Volt x Amps = Watts or Watts = Volts x Amps.

While Amps can be used as a convenient reference when the voltage remains constant, it leads to trouble in scenarios when more than one voltage is in play such as in our campers where we may have things that run at different voltages.

The smallest Eemax lists: SP2412 2400W 120V-20A 33 degree temp rise at 0.5 gal./min.

In this case, 2400 Watts = 120 Volts x 20 Amps and if we can plug in to shore power, life is good. But when we can't plug in and don't have access to a generator, things change drastically. Pulling that 2400 Watts from our 12 volt batteries changes the basic math (2400 Watts = 12 Volts x 200 Amps) plus we need to include the inverter efficiency since we are running a 120 volt appliance from a 12 volts source. This leads to:

2400 Watts = 12 Volts x 222 Amps x 0.90 (for 90% inverter efficiency, the other 10% is "lost" as heat)

Now, 2400 Watts is the power the Eemax will consume in an hour and that is a very long shower! Since our showers are likely much shorter, dividing each side by 60 min./hour gives us a more useful number calculate our shower's energy consumption. Going step-wise throught the equation transformations gives us:

2400 Watts/hour = 12 Volts x 222 Amps/hour x 0.90 (include hour assumption)

2400 Watts/hour / 60 min./hour = 12 Volts x 222 Amps/hour / 60 min./hour x 0.90 (divide by 60 minutes per hour)

40 Watts/min. = 12 Volts x 3.7 Amps/min. x 0.90 (power consumption per minute).

Thinking about our energy consumption in terms of Amps is only useful because we think about our 12 volt electrical storage in terms of Amps. In reality, a 12 volt "100 Amp Hour" AGM battery is a 1200 Watt storage device that runs at 12 volts. If we wish to maximize our battery life, we avoid draining the AGM battery below 50% so only 600 Watts is prudently available. Two 5-minute showers is 400 Watts just for water heating, 2/3 of our prudent available battery power budget. This does not include the power consumption of the water pump for the showers, nor our lights, refrigeration, radio, etc.

Our battery systems and their charging systems are expensive, heavy, hard to charge and somewhat fragile in their technology, so anything that imposes a heavy load as a percentage of their prudent capacity deserves careful consideration and system design.

[cygvan]

kzinti2...great post and very helpful...i was previously getting lost with the time components if you know what i mean...and while i was aware of inverter inefficiencies, never calculated for them..

when i came upon a few calculators last night that, i guess, laid it out in a somewhat different visual way it clicked for me.

i spent the night making a spreadsheet of my own to calculate useful usage numbers. one where i can plug in the specs of my devices im thinking of installing and what the typical usage would be hourly/daily etc..

its not unlike the calculator on the concorde website, i used the basic formulas and added a few things.

it seems ive gotten lucky with a few of my choices but water heating remains as big an energy draw as your post (and others) demonstrates.

i might just go with the coleman camper hot water thing modded to provide hot water to my faucet...

i cant see why it wouldnt suit my needs as im not adding a shower to my build anyway. its just nice to have hot water on demand in any situation really.

[louie]

So just to make sure I have my generator requirements understood if I go with the Eemax electric tankless water heater that raises the water temp. 48 degrees I would need a 3500 watt generator for it to work?
Many thanks, Louie.

[sinbad]

Originally Posted by Jeffrey

Budget permitting, consider the flatplate heat exchanger. No tank or fuel required. Of course, the engine must be warm to get warm water, but I find that the 6.0L retains so much heat that I get hot water for a long time after the engine is stopped. I installed an inline coolant pump (from Greg @ lubrication specialists) which circulates the hot coolant when the engine is off. Main drawback is no hot water on cold mornings when you awake. Then, I wait until I've driven a bit before washing, or I throw a wet cloth into the microwave for instant washing of face and body parts. (your parts may vary).

I have used the flatpate heat exchanger before and it worked great when engine was running - even at an idle. But after only a short time, a minute or so, the water was cold. Your modification with a pump solves that problem and allows the retained heat of the engine to heat the water.

What kind of pump was used? Where is Lubrication Specialists and their contact info? I assume you turn the pump on when you want hot water. Does the pump negatively affect the cooling system or do you not even know it is there? Does the heat in the engine compartment affect the pump? How long have you been using this pump? Are you still happy with it? Any suggestions?

Sinbad

[Overland87]

I traveled all over the states in a restored 1947 tear drop trailer behind my jeep and used the black solar bag shower and it worked GREAT, some say it takes to long to heat the water but I just used my camp stove to warm the water and poured it into the solar shower, low tech but the water just had to be warm so I didn't burn alot of fuel, it didn't take alot of space and I didn't have to wire or plumb it into anything.

[larrie]

X2


Larrie
89 Ford 2WD penthouse

[Ford_6L_E350]

Originally Posted by Kzinti2

Some definitions:
SP2412 2400W 12V-222A/hour or 3.7 amps/minute from your battery (18.5 amps for 5 min. shower)
SP3012 3000W 12V-278A/hour or 4.6 amps/minute from your battery (23 amps for 5 min. shower)
SP3512 3500W 12V-333A/hour or 5.6 amps/minute from your battery (28 amps for 5 min. shower)

There is no such thing as A/hour or amps/minute. I shouldn't say that. Those can exist in calculus equations for rate of change. They don't exist in ordinary electrical equations. Amps is an instantaneous measurment of of electrical flow (current). Technically, 1 amp is 1 coulomb (6.022 X 10 to the 23rd power) of electrons passing a point in 1 second.There is an Amp-Hour measurement of current and time, but it won't work with the conversion you have here.

10 Amp-Hours is equivilant to 600 Amp-Minutes. It is probably easier to leave everything in Watts and do the conversions.

2400W = 120V X 20A or 12V X 200A/90% = 222A. That is 222A continous for as long as you are drawing 2400W. 222A for a 5 minute shower is 18.5 Amp-hours from a 12V battery. Almost the same as cranking your starter motor for 5 minutes. Oh, for a short wire, you should use at least 2 gauge or larger for that current, preferably 0 gauge.

Mike