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Inverter water pump monitoring circuit

Discussion in 'Gen 2 Prius Technical Discussion' started by _echo, Jun 13, 2009.

  1. _echo

    _echo Junior Member

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    The whole inverter water pump failure issue has been bothering me for awhile now. Although mine hasn't done anything bad (knock on wood.) I have been giving some thought as to how to monitor the flow of coolant, from simple 'water wheel' type monitors to noninvasive ultrasonic turbulence detection.

    Then the idea hit me, or rather, it hit my finger.. :p
    Most PC's that run cooling fans monitor the fan RPMs. The obvious one would be a tach signal on the inverter pumps, but I didn't see one. :(

    Looking at the Gen2 wiring diagrams, one can see only two wires going to the motor. All is not lost though. We'll just have to experiment with how to monitor whether it's spinning. My goal would be to have some sort of addon widget that dosen't modify the pump (too much). So, cutting into the pump assembly is probably out. silicone-ing something to it... maybe...

    This is based on raw assumptions and might be completely wrong so... Here are some ideas if some hardware hackers out there want to work on a circuit:
    1) I'm ASSUMING it's a brushless motor.
    2) Watching the current going into the motor might be fun, but that would either require cutting the harness, or doing a fancy hall/rogowski probe. With all of the giant magnets in the car, this might affect our SNR?
    3) If it's a brushless motor, putting a coil next to the rotor assembly might be enough to pick up something usable as a tach signal.
    4) All of the brushless motors I've seen have some sort rotor position detector. This includes the big ones in the transaxle! Whether it be a hall effect assembly, or something more exotic like back EMF (hard drives, etc.) If we could get to those pins without _too_ much depotting of the pump, it _might_ be ok? It will most certainly void your warranty.
    5) The control signals to the coils track the rotor position. Those coils generate magnetic fields. All motors do that. That's just how a motor works! So maybe a magnetic probe somewhere would be helpful?
    6) I was thinking about doing some sort of vibration analysis, but such an item might not work so well in a car.
    7) A thermocouple in the water is an obvious solution, cutting into those coolant lines is not so elegant though. I want this to be somewhat invisible, and adding our own fittings into this might be frowned upon?

    I have no idea what the failure condition is like, I'm assuming either lower RPM, or a complete stall? Unless the impellers get chewed up, a pump that spins is actually pumping, right?

    I hope to never see one fail, but part of this whole post is to come up with a circuit that might offer peace of mind to all of us!

    As for monitoring, we could do something as simple as a giant piezo buzzer. If you're adventurous, you could probably acuate something innocuous to generate a 'harmless' DTC... It'll make the mechanics mad, but if you're going to do this type of hardware, you should know better!

    Does anyone have a dead/spare inverter pump to hack apart?

    Let me know if anyone is interested in such a project.

    _echo
     
    #1 _echo, Jun 13, 2009
  2. edthefox5

    edthefox5 Senior Member

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    Already installed a Inverter Temp monitor on my 07. It was down & dirty but cheap & quick & will work.
    Here's an old post of mine describing it I will paste for you: BTW, no one seem interested at all.

    Here's the paste:



    I agree with Patrick. I think when the Inverter crow bars it probably throws every code it can.

    BTW, based on so many people complaining of this pump failure I installed an inverter temp alarm test kit on my 2007 that monitors inverter temperature. Basically used my 2007 as a test bed.

    It only alarms when slight over temp of the inverter has been reached signaling pump failure. It consists of a thermostat mounted to the Inverter case:

    STC-120


    that shorts its leads together when the case of the Inverter reaches a temp of 113F. 12 volts goes into one lead and the other lead of the thermostat is wired to a 12 volt car alarm horn which is grounded. It works real good. If Inverter temp goes over 113F the car alarm horn goes off. I installed an inline fuse holder so the horn can be disconnected quickly upon activation.

    This kit can also discover an intermittent pump too which you could possibly have.

    Total cost was around $20 delivered for everything and took me about an hour to install. I recommend this kit for older Prius's because if you burn up your inverter out of warranty your looking at alot of money $2-4K not to mention if it causes a dead boot battery and you need a jump exposing your car to rookie jump starts which can total an older car and on this site we have seen many many disasters. Remember there is no dash board alarm when the Inverter cooling pump fails. It only alarms when the Inverter severely overheats and also fails to output its running voltage to system and motors which is why when it starts to overheat it begins failing and it is described as gradual loss of locomotive power and most people not knowing how bad the problem is continue to drive which only exacerbates the issue and exposes the Inverter to complete overheat and total failure. My personal suspicion is this event low or wrong run voltage to the electric motor is not good for the MG windings either.

    Short of the Transaxle & motor the Inverter plus installation is the most expensive part of our car.

    The Thermostat can be bought at Mouser for $5 with no minimum order and I got the horn new off ebay $15 delivered.

    Please PM me if you need additional info. Good Luck.
    Last edited by edthefox5; 03-24-2009 at 07:46 AM.
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    #2 edthefox5, Jun 14, 2009
  3. edthefox5

    edthefox5 Senior Member

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    Only issue I have had with it I was stuck in stop & go traffic the other day and it was 97 out. When I finally parked the car it heat soaked and 5 minutes later after parking it tripped the horn so need to move up to the next temp level of STC which I think is 130 degree's F. Which is why I call it a test bed.
    I checked the Inverter temp alot last year with a IR thermo and never saw more than 120 F so its an efficient Inverter cooler when its working.
    But If I can catch a pump failure at 130 F it would really help not destroying the Inverter. At the very least I would know exactly what the car was complaining about and deal with it accordingly.
     
    #3 edthefox5, Jun 14, 2009
  4. EZW1

    EZW1 Active Member

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    I think the easiest, and possibly the best, solution would be to install a flow rate indicator. These should be easy to come by. They're used a bunch in the aviation community. A flow rate monitor will tell you if the pump is moving fluid and you wouldn't need to be concerned with pump rpm, current flow, etc. Because proper operation of the coolant is crucial to vehicle operation and failure could lead to very expensive repairs, I'm surprised that Toyota didn't put some kind of monitoring system in place.
     
    #4 EZW1, Jun 14, 2009
  5. _echo

    _echo Junior Member

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    edthefox:
    130degF sounds a bit low, I guess my goal is a set and forget device with enough diagnostics to offer peace of mind. Your solution actually sounds way more effective than mine. Your solution is very reliable and, I actually have parts around here to do something like that. I'm not sure what is inside one of the normally 'open' thermostat devices, it might be better to use a normally closed device, that way a broken loop won't give you a false sense of security. Break open any laptop battery, and you'll find a suitable device.

    Hmm. I might go hobbit style with a vampire probe on one of the ECUs. There's gotta be a thermistor SOMEWHERE in there. (Or just use my can view :p)

    EZW1:
    A flow meter is probably the best choice, unfortunately it's most certainly not stock. My main reason I haven't pursued that since there is the small issue of breaking into the cooling loop and adding 'stuff' to the chain. My plumbing skills depend mostly on silicone and teflon tape. (!!!)
     
    #5 _echo, Jun 14, 2009
  6. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Since the inverter coolant pump is connected via rubber hoses to the inverter and transaxle, you can use a single-edge razor blade to cut one of the hoses in two for purposes of attaching your flow meter. Then when you are ready to remove your mod, just buy a new hose from your Toyota dealer's parts dept.

    I currently have 80K miles on my 2004 and am thinking about replacing the inverter coolant pump sometime this summer as a preventive maintenance move.
     
    #6 Patrick Wong, Jun 14, 2009
  7. northwichita

    northwichita .

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    I've mentioned before using a digital oven temperature gauge for my prius, I turn it on for these warm days when my ac is on. The inverter runs around 110 F, up to 130 after turning off the car for a while. Then end probe is epoxy'ed with this plumbers epoxy on top of the inverter case, I believe this gives a close temperature reading to the inside of the case. The cord runs around the outside of the door jam between the engine and the interior of the car, (directly underneath the area of the small triangle side window is a small opening ) the small cord doesn't seem to be a problem with the door seal.

    I did a web search and found with alarm digital temp gauge with adjustable preset alarm parameters, which definitely looks better that the one I have , and has a temp range of -4 to 158 F . For 20 bucks and no extra electronics to deal with, I'd suggest this option.

    Alarm Thermometer | Sper Scientific

    Note I have not used this particular temp gauge, or bought from this site.

    I've mounted with tape my temperature gauge on the top left of the dash, near the driver's small triangle window.
     
    #7 northwichita, Jun 15, 2009
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