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How hot is too hot?

Markfitz

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Joined
May 17, 2022
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Hi all,

I'm new to this forum and am hoping to find some help.

A little background, a few months ago I just completed a full solar and electrical system in my motorhome. I installed a 640 watt solar system which is paired with 300 amps of lithium battery, a 3500 watt inverter and a shore power hook up. The system was tested and has passed German regulations.

As part of my electrical build I built my own hot water tank which loops through filters and a UV light to create a recirculating shower.

In the tank I installed a 12v 300w water heating element. Wiring runs from my fuse box into a timer switch and from the timer switch to my element. Everything was working fine, when turned on it draws 25amps from my batteries and heats the water after a couple hours.

During my initial testing I noticed that the wires running from the switch to the element got very hot. Mainly on the element side, I figured it made sense because the element is heating up and that heat is travelling from the element into the wires?

Today I was inspecting my electrical system to make sure everything is ok and I noticed that the plastic insulation around the connections on my element had charred. Worrying to say the least.

I decided to turn the system on today and test out what is happening.

I used a multimeter to test the temperature of the wires after a few minutes of heating. The results seem worrying, very close to the element (within a cm) the wire is reading at 109 degrees Celsius. As you move up the wire it drastically cools and by the switch it's only warm.

I tested the wires (same guage) from the fuse box to the switch and they're not warm at all. (The run from the fuse box to the switch would be around 2 meters and from the switch to the element half a meter)

Am I correct in guessing that the wires are heating up from the heat of the element? Would thicker wires help? And or are there special wires that need to be used to connect to a high heat source? I'm thinking that inside an iron or other devices that get hot they might use special wiring?

Any help, tips or suggestions would be greatly appreciated, if you need more information I'm happy to provide it. For now I've decommissioned the heating system until I know that it's safe to use.

Many thanks,

Mark
 

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Looks like a high resistance connection. Was the terminal on the wire faulty? Possibly a loose connection at the element?
I agree. Your description sounds like a poor connection. The element is in water, right? It should not be getting hot and heating the wire, not that hot anyway.
 
Anytime your wires get hot, you are wasting energy. Wires are too small to handle the load, possibly the connectors also. What gauge wires are you using? With it pulling 25 amps, wire should be at least 10 gauge.
 
I'd agree that it looks like a bad connection, but I'd also assume you have some sort of relay and Tstat in place to actually control the element.

Do you have any type of thermostat in place to control the heating element?
 
If you are replying to my statement about the element being in water, the element (the only part that should make heat) is in the water and should be cooled to something less than the boiling point of water. So the heater is not the source of the baked leads if the element is indeed covered in water. My response was to the O.P. question, "Am I correct in guessing that the wires are heating up from the heat of the element?" The heating element (while in water) should not have heat above boiling point of water, heating the wires.
 
Hi all,

I'm new to this forum and am hoping to find some help.

A little background, a few months ago I just completed a full solar and electrical system in my motorhome. I installed a 640 watt solar system which is paired with 300 amps of lithium battery, a 3500 watt inverter and a shore power hook up. The system was tested and has passed German regulations.

As part of my electrical build I built my own hot water tank which loops through filters and a UV light to create a recirculating shower.

In the tank I installed a 12v 300w water heating element. Wiring runs from my fuse box into a timer switch and from the timer switch to my element. Everything was working fine, when turned on it draws 25amps from my batteries and heats the water after a couple hours.

During my initial testing I noticed that the wires running from the switch to the element got very hot. Mainly on the element side, I figured it made sense because the element is heating up and that heat is travelling from the element into the wires?

Today I was inspecting my electrical system to make sure everything is ok and I noticed that the plastic insulation around the connections on my element had charred. Worrying to say the least.

I decided to turn the system on today and test out what is happening.

I used a multimeter to test the temperature of the wires after a few minutes of heating. The results seem worrying, very close to the element (within a cm) the wire is reading at 109 degrees Celsius. As you move up the wire it drastically cools and by the switch it's only warm.

I tested the wires (same guage) from the fuse box to the switch and they're not warm at all. (The run from the fuse box to the switch would be around 2 meters and from the switch to the element half a meter)

Am I correct in guessing that the wires are heating up from the heat of the element? Would thicker wires help? And or are there special wires that need to be used to connect to a high heat source? I'm thinking that inside an iron or other devices that get hot they might use special wiring?

Any help, tips or suggestions would be greatly appreciated, if you need more information I'm happy to provide it. For now I've decommissioned the heating system until I know that it's safe to use.

Many thanks,

Mark
NEVER put a crimp connector on solid conductors.
I’m sure that is the issue.
Solid wire needs to be wrapped around the element terminals.
 
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Hi all,

Thanks for the replies,

So the element is sealed and doesn't come into any contact with the wires. I am not using a solid core wire as it goes against German regulations for a motorhome.

When testing the heat of the wires I also tested the heat of the connections to the element and this provided the highest temperature.

Unfortunately I couldn't find a 12v thermostat powerful enough to control this element so I had to opt for a timer switch instead. My original plan was for the element to be controlled by a thermostat.

I've attached a couple of extra photos, one of the connection to the element and one of the timer switch.

Lastly I forgot to add earlier that the connection with the charred plastic had become displaced, the wire was completely removed from the crimp and the ring was left connected but looked very crusty when I removed it.

My best guess from reading through your suggestions is thicker guage wire with better connections?

Thanks again,
 

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There you go then.
If the wires aren't getting hot elsewhere, then top quality crimp connections should solve the issue.
 
Some of the crimp terminals that you can buy currently (in US) are thinner and weaker than they should be. When in doubt, I solder after crimping to be sure of the connection.
 
Hi all,

Thanks for the replies,

So the element is sealed and doesn't come into any contact with the wires. I am not using a solid core wire as it goes against German regulations for a motorhome.

When testing the heat of the wires I also tested the heat of the connections to the element and this provided the highest temperature.

Unfortunately I couldn't find a 12v thermostat powerful enough to control this element so I had to opt for a timer switch instead. My original plan was for the element to be controlled by a thermostat.

I've attached a couple of extra photos, one of the connection to the element and one of the timer switch.

Lastly I forgot to add earlier that the connection with the charred plastic had become displaced, the wire was completely removed from the crimp and the ring was left connected but looked very crusty when I removed it.

My best guess from reading through your suggestions is thicker guage wire with better connections?

Thanks again,
I heat my hot water very similar to what you are doing but direct from the solar panels not off of the battery but I have 0 issue with either the wire ends or the wire heating up. I am pushing around 25 amps and 36 volts on 1/2 of a 1200 DC watt element and using cheap automobile grade eyelet connectors crimped on 8 gauge wire. I did however burn up a 600 watt heating element on my first try. Although I do believe that it "may be" a loose or bad eyelet and probably wires causing the overheating but I am wondering if you are burning up your heating element? It should not be since it is a 12 volt and 300 watt element. Just sounds like it may be pulling more current than 25 amps and maybe it can't handle the amps? Have you checked the element it self? Have you put an OHM meter across the element for a reading? If that element is running very low OHM's and cannot handle the amps, for some reason it may be burning it up. The lower the OHM's the more efficient it works transferring heat to the water. Just a thought since I burned one up.
 
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I've attached a couple of extra photos, one of the connection to the element and one of the timer switch.

Lastly I forgot to add earlier that the connection with the charred plastic had become displaced, the wire was completely removed from the crimp and the ring was left connected but looked very crusty when I removed it.

My best guess from reading through your suggestions is thicker guage wire with better connections?

Thanks again,

While current is flowing, use DMM to read voltage across each connection. With 10A for instance, 1 milliohm would register 10 millivolts.

Your wires are shown on top of a nut, which is on top of a busbar.
Connection on top of a nut (or washer) is often a source for large voltage drop and heating. Try moving ring terminal below that nut.

In this case, looks like busbar is also on top of a lower nut. But maybe that nut is an integral part of the threaded terminal??
In most applications, neither nut nor threaded stud (or bolt if used) is a good electrical path. The underlying terminal is the path, and nut/stud/bolt is just a mechanical clamp.
 
I heat my hot water very similar to what you are doing but direct from the solar panels not off of the battery but I have 0 issue with either the wire ends or the wire heating up. I am pushing around 25 amps and 36 volts on 1/2 of a 2400 DC watt element and using cheap automobile grade eyelet connectors crimped on 8 gauge wire. I did however burn up a 600 watt heating element on my first try. Although I do believe that it "may be" a loose or bad eyelet and probably wires causing the overheating but I am wondering if you are burning up your heating element? It should not be since it is a 12 volt and 300 watt element. Just sounds like it may be pulling more current than 25 amps and maybe it can't handle the amps? Have you checked the element it self? Have you put an OHM meter across the element for a reading? If that element is running very low OHM's and cannot handle the amps, for some reason it may be burning it up. The lower the OHM's the more efficient it works transferring heat to the water. Just a thought since I burned one up.
Thanks for your suggestion, the outside of the heating element is getting incredibly hot but I couldn't figure out if it was the wire heating it or it heating the wire. I would like to test this tomorrow, I haven't tested OHMs before and am wondering if you could share some knowledge on what to look out for?

I would add that when I turn the heater on I can see on my battery monitor that it is drawing 25 amps when switched on, not sure if this makes a difference to the test or not?

Thanks again for your reply!
 
While current is flowing, use DMM to read voltage across each connection. With 10A for instance, 1 milliohm would register 10 millivolts.

Your wires are shown on top of a nut, which is on top of a busbar.
Connection on top of a nut (or washer) is often a source for large voltage drop and heating. Try moving ring terminal below that nut.

In this case, looks like busbar is also on top of a lower nut. But maybe that nut is an integral part of the threaded terminal??
In most applications, neither nut nor threaded stud (or bolt if used) is a good electrical path. The underlying terminal is the path, and nut/stud/bolt is just a mechanical clamp.
Hi Hedges,

I'll try and remove the nuts tomorrow and test to see if this suggestion works and will let you know.

Greatly appreciate the advice,

Mark
 
Thanks for your suggestion, the outside of the heating element is getting incredibly hot but I couldn't figure out if it was the wire heating it or it heating the wire. I would like to test this tomorrow, I haven't tested OHMs before and am wondering if you could share some knowledge on what to look out for?

I would add that when I turn the heater on I can see on my battery monitor that it is drawing 25 amps when switched on, not sure if this makes a difference to the test or not?

Thanks again for your reply!
First is your battery monitor correct? Can you check it with a DC clamp meter? Second, you can OHM the element by setting your meter to check OHMS. Disconnect your wiring going to the element, I know it is a pain to disconnect. Then disconnect the straps that tie both sides of the heating element. Touch opposing poles on the element. If you read 0, then you are touching the wrong poles at the same time. Change and test different poles. AC elements range 6 to 12 OHMS. DC elements range in the 1 to 3 OHMS. Also see if both sides of the elements read then same. Let us know what you get.
 
You might want to double up the wires feeding each element.
Get a pair where they are, then add another pair to the other element.
 
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