DIY electric water pump - on the cheap

[Daox]

Another idea I'm currently thinking about implementing on the Tercel is an electric water pump. The Tercel is blessed to be a base model, so it doesn't have power steering or A/C. That leaves the alternator and the water pump left on the accessory belt. I'd ideally like to eliminate both of those accessories and not have any accessory loads on the engine, and no belt losses. The alternator delete is easy. I've done that already on the Paseo I had. The water pump is slightly more difficult. I've seen only a couple people do them here and they seem to be ridiculously expensive (hundreds of dollars). While not super inexpensive, my proposed setup is quite a bit cheaper than that. If you want to scrounge for parts, it'll definitely drop the price.






My idea is first off not to replace the OEM pump, but instead just drive it with an external electric motor. There are tons of small motors out there that will work. I was thinking of using one of those little permanent magnet scooter motors. They're rated for way more than enough power to spin a water pump around. You can pick these up for nearly free if you can score a dead scooter, or off ebay for ~$30. Here is a picture of one I've had kicking around for a couple years just waiting to be put to good use.






Of course, you'll likely have to derate them for 12V (vs 24-48V). I'd recommend ~100W derated for anything up to 3.0L. This fits inline with OEM electric water pumps. Oversized motors are fine as we'll be programming this with an arduino and we can slow it down to sip as much power as we choose. Mine happens to handle 16.5A. That gives me (16.5A * 12.5V = ) 206W of power. Its WAY oversized for this application where I think I'll probably only need about 50W max.






As mentioned, an arduino will be used to control the motor speed. We don't just want it running full blast as that would be quite wasteful. So, my current idea is to monitor coolant temperature and the MAP sensor and vary speeds accordingly. The warmer the engine is, the faster the pump runs. The higher the engine load, the faster the pump runs (with a few second delay after loads have decreased to take out any heat retained in the cylinder walls and head). This keeps the programming and wiring quite simple.






Now, the arduino can't handle providing anywhere close to 100W of power to the pump, so you need some other board with some transistors so we can PWM control the pump accordingly. I was thinking of making my own (and you could to save money), but then I found this 10a motor controller shield that makes life a lot easier. Just plug in the motor wires and you're ready to go. It even handles reversing the motor direction programatically if you want.

The connection between the motor and pump isn't figure out yet. Chain or belt will be the way to go. There isn't enough room to direct drive it as the frame member will get in the way.

All in all, this setup, if purchasing all components new would cost ~$70 plus shipping of the components. If you scrounge parts you could put this together for $20.

I like this idea because it'll work great in combination with the alternator delete, block heater, and using engine coolant to heat the transmission. The engine and drivetrain could be preheated before even starting the car just by plugging in to recharge overnight. It also allows you to get heat in winter when your engine is off.

So, that is the general idea. Its far from being implemented as the car isn't even running yet. But, I figured it would be fun to share, talk about, and refine the idea with you guys.

[oil pan 4]

I have the electric water pump mod and I don't recommend it, especially if you want to do an alt delete.

Just don't give up reliability with too much electronics.

That motor is only slightly bigger than what my electric water pump uses. Mine uses 5 or 6 amps and cools my 395 cubic inch diesel and 2 water cooled turbochargers pretty well.

Since this is a permanent magnet motor you will likely find that on 12v it might not draw any where near 16 amps.
On a lot of devices when you cut the DCV in half that usually cuts the amps roughly in half, reducing your wattage to around 1/4 of the original rated power.
So you might not even need a controller.

[Daox]

So you wouldn't do it for reliability reasons? Why not with an alternator delete?

[oil pan 4]

The reason why I would chose a belt driven coolant pump over an electric coolant pump is I figure less electrical draw makes for a better alt delete. You can have both, if you know you will never drive the vehicle for more than a few hours before being able to recharge. Once you rule out time and distance between rechargings as a problem then go for it, I bet it will work great.

An actual purpose built electric coolant pump isn't recommended for street use but I have ran mine up 12 hours at a time driving from New Mexico to Virginia. So electric motors and pumps aren't the problem.
I see potential problem with that motor controller. I work with bigger various motor controllers and they all have one thing in common, they like to quit and they seem to do it at the worst possible time.

If your travel situation allows an alt delete and electric water pump to coexist then first try running the motor straight off 12v and if you believe the motor uses too much power then add a big resistor to the circuit and reduce power to the motor that way.
Its not as efficient as a motor controller but its not going to fail.

[Daox]

Are these failures due to cheap components and bad design, or heat and pushing them to their limits? What should I be looking out for? Obviously bad design is a risk we take with anything we buy these days. Using a component below its rating should improve reliability and life though.

[Daox]

I actually would like to remove any engine load and move it to battery operation as its less work the engine has to do. If is too much for the battery, I need a bigger battery. If I keep the controller, I can also optimize the electrical load of the pump. The trade off is obviously more complexity and reduced reliability. Is it worth it? I dunno, we'll get to testing at some point I hope!

[jeff88]

I love when Daox gets the mod bug!

[jeff88]

If you're going to drive the pump off of a belt off of the motor, doesn't that defeat the purpose of the electric pump? Wouldn't you be doubling the losses, the belt and now adding the electric drive (the electricity has to come from somewhere)?

[Daox]

The belt or chain would only connect the electric motor to the water pump. So, the belt losses would be removed from the engine. The electric motor would have to deal with the belt losses instead. Suggestions on how to better couple the motor to the pump are quite welcome.

[Ecky]

Subscribed.

Sounds like you're building a hybrid of sorts.

Made me consider though, that Honda seemed to let the engineers go wild with the original Insight, and ended up with both an alternator delete and electric power steering, but they kept the belt driven water pump.