diy solar

diy solar

Pros and cons 48v dc water heater vs 120 ac off grid

Sparky7

New Member
Joined
Jan 31, 2023
Messages
116
Location
Wi
I would like to us excess power during the summer months to heat my domestic water. What are the pros and cons? Should I go directly from my 48 V system or through the inverter 120 V?

It is currently set up for 120v.
 
Find 48v DC elements and feed those would be more efficient and cheaper than an inverter capable of feeding the 120v 2kw elements or whatever your water heater calls for.
 
I think it comes down to cost vs complexity.

On one hand, finding 48v elements and running the required guage of wire to feed them is complex. You're going to have to spend money to buy specialty elements and thicker wires, and have some way of engaging the heaters only when you're in "excess power" mode which is probably something like a Hydro controller with dump loads terminals.

On the other hand, what is the wattage draw on that water heater? Even if it's only 120v you still need a way to invert that much wattage. It will be easier to wire up and you don't need specialty elements, but now you need to figure out some sort of relay system to only power on when in "excess power mode" which could be as simple as jacking into a remote switch or as complicated as an Adrino with a relay and supplemental power supply and the like.

Both options have their pro's and cons. My choice personally would be a standard 48v hydro controller for the dump load going to 48v elements. But I like the simplicity of that. The choice is ultimately yours.
 
I think it comes down to cost vs complexity.

On one hand, finding 48v elements and running the required guage of wire to feed them is complex. You're going to have to spend money to buy specialty elements and thicker wires, and have some way of engaging the heaters only when you're in "excess power" mode which is probably something like a Hydro controller with dump loads terminals.

On the other hand, what is the wattage draw on that water heater? Even if it's only 120v you still need a way to invert that much wattage. It will be easier to wire up and you don't need specialty elements, but now you need to figure out some sort of relay system to only power on when in "excess power mode" which could be as simple as jacking into a remote switch or as complicated as an Adrino with a relay and supplemental power supply and the like.

Both options have their pro's and cons. My choice personally would be a standard 48v hydro controller for the dump load going to 48v elements. But I like the simplicity of that. The choice is ultimately yours.
The element that is in the water heater right now is 120 V 1500 W. When I purchased the water heater, I thought it was AC or DC but I didn’t know what I was doing. The sales rep was also dishonest.

I called a different company and they set me up with a relay and a whizbang Junior for my Magnum inverter/midnight classic charge controllers. I ran two 8 gauge wires about 50 feet from the inverter to the water heater. This was while I was planning to do a 48 V system.

I called the water heater company and he said I could put a 48 V element in the tank No problem but the thermostat likely would not handle that current.
 
Yeah, sounds like you're almost all the way there, you just need the DC elements and thermostats...

Or a 2kw inverter that can use the existing elements and thermostats that can be controlled by the whizbang.

Basically you're half way in between.
 
Yeah, sounds like you're almost all the way there, you just need the DC elements and thermostats...

Or a 2kw inverter that can use the existing elements and thermostats that can be controlled by the whizbang.

Basically you're half way in between.
So a 2kw inverter just to make sure I don't overload my 4400w inverter?
 
Basically, if you only want to use it as a dump load, but if you have to de-rate your inverter's output because the the heater might come on...
So what would this look like? Being I have two charge controllers. Would one of the two be connected to the 2KW inverter that would feed the water heater?
 
No, both would connect up to your batteries as normal, you'd just need a dump controller to send power to the 2kw inverter (or toggle the remote power switch) to turn on when you've got the "excess power" available. Basically the dump controller would just be another DC load on the system and if it didn't exist there would be no change on the current system setup.
 
No, both would connect up to your batteries as normal, you'd just need a dump controller to send power to the 2kw inverter (or toggle the remote power switch) to turn on when you've got the "excess power" available. Basically the dump controller would just be another DC load on the system and if it didn't exist there would be no change on the current system setup.
Thank you
 
If it's excess power already then there's no reason to overcomplicate things with DC.
agreed... and when wanting to make it "smart" :
buy a tuya breaker or SonOff 16A smart switch, and have that turn on when battery full, or more power being generated than can be used

easyl and very KISS
 
Any really smart system would have proportional control. You can't imagine how nice it is to pull excess power directly from an array avoiding larger inverter and battery. And most PV systems have a lot of excess. As a bonus, my laundry has a separate tank just for washing and all cycles use hot water.
 
Any really smart system would have proportional control. You can't imagine how nice it is to pull excess power directly from an array avoiding larger inverter and battery. And most PV systems have a lot of excess. As a bonus, my laundry has a separate tank just for washing and all cycles use hot water.
I like this idea but the solution is probably difficult.
 
I would like to us excess power during the summer months to heat my domestic water. What are the pros and cons? Should I go directly from my 48 V system or through the inverter 120 V?

It is currently set up for 120v.
I am setting up to do that this Summer. I have purchased a new 30 gallon hot water tank that I swapped out the 240v-4500w elements with 120v- 2000w elements. This tank is replacing the present tank. My controls are a MTS to switch between grid and inverter supply and a simple 30amp 2 pole on/off switch already used now to control when I want hot water.

The idea is in the afternoon when my batteries are charged I will switch on the hot water tank and run it for a couple of hours. That will give me hot water to shower and do a load of clothes or run the dishwasher. After which the water heater gets switched off. Since I do not need hot water all the time this should work. But I will see once everything is setup.
 
I have several I've shipped working boards too and more than two years later have never been installed. Just drilling a hole is far too complicated for some. Those who have built their own have been more motivated. Here is someone whit no prior electronic experience who built his own. He added a few extra FET because he couldn't get high current ones locally and added a few extra capacitors. He started out with just heating water, but a charge controller could be added. This is his video in winter operation.

 
Since the heater has dual elements, couldnt you use one element for DC and leave 1 on AC?
 
I am setting up to do that this Summer. I have purchased a new 30 gallon hot water tank that I swapped out the 240v-4500w elements with 120v- 2000w elements. This tank is replacing the present tank. My controls are a MTS to switch between grid and inverter supply and a simple 30amp 2 pole on/off switch already used now to control when I want hot water.

The idea is in the afternoon when my batteries are charged I will switch on the hot water tank and run it for a couple of hours. That will give me hot water to shower and do a load of clothes or run the dishwasher. After which the water heater gets switched off. Since I do not need hot water all the time this should work. But I will see once everything is setup.
I like that idea and thought of doing something Manually but I’m very seldom home during that time of day. Good idea though.
 
Back
Top