Coolant booster pump control

How about the LM339?

Any comparator will do as proof of concept. Substitute a standard LTS-supplied model .

The 339 has a wider single supply range.

The OP already has a LM311, but I didn't have a model of that.
If you're desperate for the 339 model, here it is:

alec_t said:

Based on the figures in post #18, here's a suggested circuit. I've attached a zip file for simulating the circuit.
The comparator receives a reference voltage which, like the voltage at the temp sender terminal, tracks the battery voltage. The trip point is thus not significantly affected by battery voltage and no regulator is necessary.
The trip point is adjustable with a trimpot. R3 sets the amount of hysteresis, so may need to be tweaked.
Supply decoupling and spike suppression components are not shown but would be advisable.

Click to expand...

Thank you Alec_T, That's almost the setup i have now, but still needs some tweaking here and there. IE resistor values need to be upped a bit.

I see you have a pull up resistor on the output, but would that be needed for the LM311 since it has a built in Transistor already?

Also need to look back at how to do the Decoupling and spike suppression part.

Just wish i had the software to simulate it. oh'well.

Thanks again

KeepItSimpleStupid said:

Nope, there is something there, not necessarily a regulator. because it's not 12 V and as predicted: 7.5/8.63*2.37 = 2.06 which is really close to 2.06 (Identical).

Click to expand...

Would resistors count then? I haven't determined how they are connected to the coil winding of the gauge yet thou.

The resistance between the 3 terminals on the gauge itself are P to S = 186.5 ohms, P to N = 280 ohms, S to N = 246.4 ohms (P = Power, N = Ground, S = Sender)

I see you have a pull up resistor on the output, but would that be needed for the LM311 since it has a built in Transistor already?

Click to expand...

There is only a very feeble internal pull-up via a transistor emitter-base junction, so I think an external pull-up is necessary.

Just wish i had the software to simulate it

Click to expand...

Can't you run LTspice? It's a free download from Linear Technology.

in your first post, you mentioned turning on a pump or something: Automotive relays such as this **broken link removed** are used all of the time. You can usually but a plug and the relay. It takes 133 mA to drive the relay. The sink current is feeble, maybe 10 mA or so. If you want to drive a FET, you;ll need a pull-up.

Even the LM339 output is feeble, so you can't drive a relay coil directly. You could easily use a FET or say an LM395T which is a very strange beast. It's called an ultra reliable power transistor. You can short it's output and it doesn't care. Vce (sat) is higher.

Anyone doing automotive stuff, should read this: https://www.google.com/url?sa=t&rct...=o4rV1eYkLLwFztqJVds1hw&bvm=bv.80642063,d.eXY

In the spike protection, you have to use 400 PIV or greater diodes. So, at a minimum 18 V Transorbs or TVS diodes and a iN400x (200 PIV) reverse biased diode to clamp stuff at -0.6 V or less. Bypass caps are USUALLY ceramic and around 0.1 uF. It;s important to install them close to the IC power pins.

Don't forget the diode across the relay coil. Radio Shack may have the LM339 in stock: **broken link removed**

alec_t said:

There is only a very feeble internal pull-up via a transistor emitter-base junction, so I think an external pull-up is necessary.
Can't you run LTspice? It's a free download from Linear Technology.

Click to expand...

LTspice! DOH!. yah got that, kinda fun for me to try and get around it and make things how i need it, and to know whats what. But yah i got your schematic to work on it.

Got another question since KISS says the LM311 can't drive a relay, Once again like my other project i shelf, i need to trigger the relay on the low side (ground) just reversing the "inputs" (Sense and reference) will do that right?

I'll experiment with it tonight, it's easily enough to swap the two pins over with the jumper wires If that works then i can use a NPN transistor to drive the relay. But then i also would need a pull down resistor instead of a pull up.

KeepItSimpleStupid said:

in your first post, you mentioned turning on a pump or something: Automotive relays such as this are used all of the time. You can usually but a plug and the relay. It takes 133 mA to drive the relay. The sink current is feeble, maybe 10 mA or so. If you want to drive a FET, you;ll need a pull-up.

Click to expand...

Yep, wanting to turn on a pump which means i needed a relay, since even i know that the LM311 won't power a Electric water pump by itself, So one would think that a relay would of been attached to the output

Will be using a Hella p/n: 933332011 which is a 40amp relay with a coil resistance of 85 ohms, which at 14V is around 160 mA

To reverse the output, reverse the inputs - YES!

Let's ask another question:
a) Are you OK with grounding the relay to turn it on or
b) Do you have tis dire want for one side of the relay to be grounded?

We are dealing with a harness that's already wired up with the relay being switched to ground to turn it on, but it is not impossible to rewire it so it's switched to positive (high).

So having the circuit trigger the relay by grounding it will make things simpler.

Good. That means you can do it with a FET, the LM395T and/or a low side driver IC. The latter two offer protections.

I briefly found a SMT FET, which you probably don't want: **broken link removed**

It has to be N channel
Vgs max has to be greater then the electrical system. >18 V min
Vds has to be greater than the electrical system
Rds(ON) has to be small
Vgs (thresh) is where the FET starts to conduct. (Look at the graph).

One of the first things you have to do is pull down, the gate such that more than the leakage current is consumed and it guaranteed to be off.
You should always place some resistance in the gate. 100 ohms is fine. it will work without it, but get in the habit,

12 V at the gate is definately enough to turn the FET fully on. That voltage will be supplied from the pull-up resistor. You will hardly need any current, but it has to be bigger than what your pulling the gate down at. The LM311 can supply at least 10 mA, so 100 uA to 1 mA should be fine. The comparator transistor should be in saturation when the relay is OFF.

So, this gismo will turn on your relay when the comparator is OFF. The FET will be turned on by the pull-up.

The relay coil needs a reverse biased diode across the coil (50-400 PRV). This is best done near the relay, but doesn't have to be.

The LM395T is a wierd beast, but it's protected. That transistor would work too, but it's not a FET.

The TDE1737DP **broken link removed** is an example of a low side driver which would work. You might need a like a 2.5 or 5V reference as well.

If you haven't bought electronic parts www.digikey.com should work. There is a Canadian website: https://www.digikey.ca/