What is this device in my engine room?

[hd002e]

In my new to me boat, the solar charge controller has a “DIVERT” connector and that goes theough a 10A fuse and into this device sitting in my engine room. I am guessing when the batteries are fully charged it diverts excess power to this device but what is it?

[captain465]

Wirewound resistor. A dummy load to disperse excess current.

[redneckrob]

Strange because solar doesn't need a divert load, it only makes power when it's attached to a load. Perhaps it is left over from a wind installation and the person doing the swap didn't really understand solar?

[hpeer]

A poor picture of mine.

I have an AeroGen wind generator. The D499 may use rhe same controller and divert resistor.

[hd002e]

INTERESTING! The charge controller is currently only connected to solar panels but I understand that there is an option to hook it up to a hydro generator as well, maybe that can generate excess current if the batteries are fully charged?

[hpeer]

It would be really helpful if you were to sketch out your set up.

It may well be the best thing is to get a different controller. Often that kind of controller is pretty inefficient for solar panels.

[hjohnson]

Originally Posted by redneckrob

Strange because solar doesn't need a divert load, it only makes power when it's attached to a load. Perhaps it is left over from a wind installation and the person doing the swap didn't really understand solar?

Depending on the time of year and location, it might make sense even with just solar. If you're in the PNW or further north, keeping your engine compartment warm makes it a lot easier to start the engine in winter, and also keeps things dryer. While I don't have something like this on my boat, we do make use of waste heat from a couple of things to try and keep the mildew down.

[hd002e]

Would this device create heat?

Originally Posted by hjohnson

Depending on the time of year and location, it might make sense even with just solar. If you're in the PNW or further north, keeping your engine compartment warm makes it a lot easier to start the engine in winter, and also keeps things dryer. While I don't have something like this on my boat, we do make use of waste heat from a couple of things to try and keep the mildew down.

[hjohnson]

Originally Posted by hd002e

Would this device create heat?

If it was connected and being used as a dump load by the controller, absolutely. The controller would direct excess energy into it, and that would be converted to heat by that resistor.

Unrelated to ny own boat, i work with a small power utility. Our old mechanical governors on our hydroelectric power plant are well past the end of their lives. One of the options we’re looking to replace at is a load bank governor. Rather than controlling the water to the turbine, it will blow excess energy into heat (in our case, up to 300 kilowatts). It’s faster, cheaper, and more stable than controlling the water flow.

[GoodShipLolipop]

Originally Posted by hd002e

Would this device create heat?

Everything that consumes power dissipates energy (typically heat, also some sound, maybe radio waves, etc.) equal to the power consumed. First law of thermodynamics.

[hpeer]

It is very similar to an old fashioned electric cook top coil. It obviously does not get THAT hot, but same principal. Run excess current through it and turn that energy into heat which dissipates. You could do it with a water heater but I seriously doubt it would be worthwhile.

I only infrequently get enough heat to be noticeable to the touch.

[goboatingnow]

I’d say it was installed in error no-one uses this to space heat.

[skipgundlach]

Originally Posted by hpeer

It is very similar to an old fashioned electric cook top coil. It obviously does not get THAT hot, but same principal. Run excess current through it and turn that energy into heat which dissipates. You could do it with a water heater but I seriously doubt it would be worthwhile.

I only infrequently get enough heat to be noticeable to the touch.

To your comment about water heaters, there are dual-element water heaters which use just that: Excess 12VDC power goes to making hot water.

Downside to that is that in periods of full batteries and no control on the diversion, you COULD (not likely, but far from impossible) boil the hot water in the tank, generating the overheat/pressure valve releasing.

OTOH, if you're in a really cold area and have, for some reason, lots of extra amps, heating the space may be a good thing. But for solar, an MPPT controller is far better use of the power generated...

[Boatwright]

It's a big resistor from an older charge control setup. I suggest you look into a modern MPPT solid state controller. It will more efficiently charge your batteries and will also have a nice finned heat sink to dissipate heat. They are not too expensive and have other useful features.

[GordMay]

How hot a resistor gets, is determined [primarily] by how much power [watts] you run through it.
The passage of current through a resistance produces heat. The heat produces a rise in temperature of the resistor, above the ambient temperature. Resistors are rated to dissipate a given wattage without exceeding a specified standard “hot spot” temperature, and the
physical size is made large enough to accomplish this.

The wattage rating of resistors, as established under specified standard conditions, is defined as the “Free Air Rating” (“Full Rating” or “Maximum Power Rating”). Several standard methods of rating are in use, based on different service conditions. The method of both
the “National Electrical Manufacturers Association” (NEMA) and the “Underwriters’ Laboratories, Inc.” (UL) can be described as follows:
The relation of the “Free Air Watt Rating” of tubular type, vitreous enameled resistors to the physical size, is to be set at such a figure that when operated at their rated watts, the temperature rise of the hottest spot shall not exceed 300°C (540°F) as measured by a thermocouple when the temperature of the surrounding air does not exceed 40°C (104°F). The temperature is to be measured at the hottest point of a two-terminal resistor suspended in free still air space with at least one foot of clearance to the nearest object, and with unrestricted circulation of air.

Power generated by resistor is: Power, P (Watts) = I x I x R

Heat, H (Joules) = (I^2) x R x t (time in seconds)