Dump Load Diversion

faroun · Feb 27, 2014

Hello every one.

I am trying to build a simple circuit to divert energy from/away from battery bank when voltage exceed the battery voltage capacity.

It is a 48vdc battery bank, I like the diversion circuit to send a voltage reading no higher than 12vdc to engage a relay that will light up a 1500watt heater.

The diversion circuit should be in the off position until it reaches 59vdc, then it sends the 12vdc signal to the relay. also the circuit should go back in the off position ones it dropes below 59vdc.

Looking forward for your help...thank
Faroun

dr pepper · Feb 27, 2014

A voltage comparator will do the trick.
Note that some histeresys would be required, ie maybe switch on the heater at 59v and switch off at 58, if switch on and on are the same the circuit will oscillate.
If you can follow it heres a page on comparators and a circuit that will drive a relay, if your relay is on the large size use a smaller relay to power the larger one.

**broken link removed**

faroun · Feb 28, 2014

Thank you for your help full response. i will check it out. any specific circuit you recommend? and yes 59on and 58off is doable

sam

Reloadron · Feb 28, 2014

Per drpepper's suggestion you want to use a comparator circuit. The attached drawing is close to what you want. For a single comparator an LM311 would do. The drawing shows a LM339 which as drawn is 1/4 of the 4 comparators in a LM339. The circuit as drawn runs on 12 volts regulated. Since you are using a relatively high voltage R3 & R4 comprise a 10:1 voltage divider. R1 & R2 set the level (reference) and could be replaced with a potentiometer, as drawn the level would be 6 volts or 60 volts at the input to R3. V1 is just the 12 volt power to power things and V2 simulates the actual input voltage. The drawing is a rough of what you want. R6 simulates a small slave relay coil. You will need to drive a large DC contactor to switch your actual load rated for the load. For example 60 volts into a 1500 watt load full current would be about 25 amps so your switching contactor should be rated at a minimum of 30 amps. Capable of switching the load.

How much electrical / electronic experience do you have?

Ron

faroun · Feb 28, 2014

good info. from scale 1 to 10 i am only 4 when it comes to electronic experience.
but you guys seam to know what i am requesting, and i should be ok if i follow your instructions.
i am going to read the components specs in the diagram, for step one, and step by step i should be able to do it.
others said to me to buy an already made controller, but where is the fun in that, i do like the challenge and
the learning part.
thanks

Reloadron · Feb 28, 2014

Buying a turn key controller was my next suggestion if you were uncomfortable with all the electronics.

You will note my rough drawing does include some hysteresis like shown in the link.

Ron

faroun · Feb 28, 2014

Ron, this project will keep me busy for a while, it is worth it. you can call me "Project Dumpo" lets see when i succeed.
this post may die for a while, but i will post any significant conclusions.
for any other member, please post any recommendation you see fit for this project.
thanks

NorthGuy · Feb 28, 2014

Reloadron said:
For example 60 volts into a 1500 watt load full current would be about 25 amps so your switching contactor should be rated at a minimum of 30 amps. Capable of switching the load.

I wanted to add that if the load is DC then the relay must be rated 30A DC. AC rating for the relay is usually much higher than its DC rating.

faroun · Mar 9, 2014

the simulation for this circuit did not end with good result. I must be missing something. the values in the image are the results when simulation is running.
any suggestions.

thanks

faroun · Mar 9, 2014

here another setup. is this any good or it can be cleaned up?
i am not the creator of this. it was provided to me by another helper.
thanks

alec_t · Mar 9, 2014

There is something weird with your simulation. R1 and R2 should result in 6V (not 11.1V) at the inverting input of the opamp.

faroun · Mar 11, 2014

here is yet another dump load circuit. i am showing the inverting and none-inverting status.
can this work can it be cleaned up a bit?
thanks

faroun · Mar 11, 2014

here is another circuit layout. i am getting stupid with this.
i think all i am asking is, what is the best circuit and can it be improved on?
i hope you can help.
thanks

alec_t · Mar 11, 2014

Where is the dump load? The FET will pass only the opamp supply current.
Why are you driving pin 2 (inverting input) at a voltage greater than the opamp supply voltage?
What are D3 and D4 for?

faroun · Mar 11, 2014

is this a bit better? thanks for your input, i do appreciate all the help.
thanks

faroun · Mar 11, 2014

I am working on the dump load fet assembly. i am going to use the rf540.

faroun · Mar 11, 2014

this is the FET assembly i put together. all i need is an advice if what i am doing can result in a successful story.

thanks

NorthGuy · Mar 11, 2014

It may not be a good idea to parallel so many mosfets. If they're different, then all the current may go through one "best" FET instead of sharing. It's better to have one big FET able to switch 30A with a big heatsink of course.

You also can attach a separate load to each FET. It'll be hard to come up with 30A 5oV load anyway.

faroun · Mar 11, 2014

ok, all FET will be the same, the reason i placed so many, so just in case some fail, others can carry on.
i will take your recommendation into consideration, to separate them.
my biggest worry is that my step down/control circuit is missing something,
it is so simple, but it seams to function in simulation, maybe in the real world it will fail.
will see. more suggestions are welcome.
thanks

NorthGuy · Mar 11, 2014

You must have a huge wind turbine if you want to divert 1.5kW. It would be a good investment to buy a controller, which will do a lot of additional stuff, such as maintaining the most efficient speed, emergency stopping etc.

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