Toyota Prius 12V Charging System Functional Test

John from Ogden Educator Posted   Latest  
Demonstration
Electrification
Electrical
2017 Toyota Prius Two Eco 1.8L (2ZRFXE) (P610)
12V Battery (Auxillary Battery) Low Voltage
No Ready Lamp
Car Shuts Down While Driving

In preparation for a Hybrid and Electric vehicle class I was teaching in July, I decided to try and find the procedure for testing the output of the DC-DC converter (The equivalent of an alternator) on Toyota Hybrids. I discovered that it has been the same procedure across all four Prius generations here in the U.S.A.. Depending upon the model year, the procedure is found under Power Source / Network - Charging System section of the Toyota service information. It can also be found as the last step in some DC-DC converter DTCs. The procedure was somewhat confusing for me comprehend, but after trying it a few times it made sense. I decided I had better document the procedure before I forgot how the test is supposed to be performed. 

I believe this test procedure will work on just about any hybrid or electric vehicle if you can access the correct cables. It is my understanding that the DC-DC converter should always be able to supply enough current for the total vehicle electrical load (an unmodified vehicle) as well as charge the 12V battery at the same time. 

I will be researching other hybrid and electric vehicle auxiliary battery charging system tests during the coming semester. I will let you know if I find anything significantly different.

Is your Prius 12V battery going dead? Learn how to check the on-car 12V charging system (DC-DC Converter) with this video. youtu​.​be/_V9PiOpaxyE&nb…;

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Michael from Rochester

 

Owner/Technician
 

Great job John. I like seeing this content. I feel like my knowledge of Hybrid vehicles is not where I want it to be. I like to absorb whatever I can and appreciate you sharing your knowledge. In your video you said that the older gen Prius‘ seem to draw a lot more amperage with the headlights on. Do you think that the newer ones draw less due to them using a LED bulb system vs the high intensity discharge? That was my initial thought. 

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John from Ogden

 

Educator
 

Thank you! The second generation Prius uses HID headlights, and the third and 4th have optional LED headlights. The LED lamps draw much less current.

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Dr. from Port Angeles

 

Engineer
 

Hi John:

Very informative video and thanks for all of the time & effort to go through Toyota's process. However, I think an alternative (and overall more technically sound test) that may provide some additional findings would be to use a load tester and an oscilloscope. Although Toyota prescribes a different process, when testing power electronics (whether automotive or otherwise) loading and tracking current, voltage, and temperatures (over a wide power and temperature sweep) provides a more thorough testing and diagnostic methodology. The scan tool (in some cases) can help to augment this testing. It's tough to get thorough results with a voltmeter. The rationale for this would be the following:

1. Power electronics need to be load tested over a longer period to test the DC-DC converter output stage.

2. Load testing provides a method of checking output vs. operating temp. vs. output current fade throughout its entire output band.

3. The oscilloscope will permit the testing of DC-DC converter voltage ripple (not current ripple) and any noise that may surface at different load levels.

4. Load testing permits testing of any current or voltage drop out at various load levels. 

5. Using load testing methods, augmented with scan tool PIDs (and possibly some output controls or special functions), can help identify intermittent or more difficult failure modes. 

6. Some of the higher output DC-DC Converters (e.g., 140 - 200 Amps) may use dual channels (2 internally connected parallel circuits) to provide final current to the output - which means that one channel may be working fine at the lower current ranges but, failures can occur at the upper ranges. This means that the system needs to be loaded at different levels with a load tester to test both channels for voltage, current, and temperature.

From an educational perspective, I had always hoped that automotive programs would start teaching technicians more about power electronics to provide them a solid background about testing and diagnostic methods with sound technical grounding. Instructing the techs in using standard testing and diagnostic techniques for battery packs, power inverters, electric machines, etc., etc. would also help. Each OEM has their own "spin" on how they testing a system or component but, there are standardized (and well proven) testing and diagnostic techniques from the electronics and energy industries that should be considered for use in the automotive service sector. Load testing while monitoring voltage, current, and temperature is a proven method of testing power electronics.

Just my 2 cents.......keep up the good work on the videos!!!

Mark

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John from Ogden

 

Educator
 

Hello Mark,

Thank you for your remarks, great suggestions, and additional information. I was not aware of dual channel DC-DC converters, but it makes sense. The Toyota method in the video has the technician turn on all of the electrical circuits possible in the vehicle to load the circuit. This method of testing could be run for hours if needed while watching scan tool PIDs of temperature, current, voltage, etc.. The Chevrolet Bolt EV and the two generations of the Volt we have in our shop call for a carbon pile load tester in their Accessory Power Module (DC-DC converter) testing as the preferred method of loading the circuit. The alternate method is some scan tool function that I do not fully understand. The carbon pile testing can not be performed for a long period of time without overheating (our old VAT-40 would overheat). I will have to try the methods of testing you suggested in my classes this semester. I am looking for some additional feedback from you and everyone else:

1. What do you suggest for a external variable load tester that would not overheat over a long period of time?

2. The only quality variable carbon pile load testers I can find are from Associated Equipment out pf St. Louis, MO. Are there other quality options I should consider?

I have the Midtronics GRX-5100 with its massive air cooled resistors, but I cannot see a way to use them on a low voltage system or to make it a variable load.

I share your educational perspective. We are working towards that in our basic and advanced automotive electrical classes. For now, the best thing I think I can do for my students is to teach them to follow and perform the prescribed procedures in each manufacturers service information.

Thanks again,

John

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Dr. from Port Angeles

 

Engineer
 

Hi John:

Please see my responses to your questions:

1. What do you suggest for a external variable load tester that would not overheat over a long period of time?

Purchase a blower to increase airflow through the unit. If the correct minimum amount of airflow is utilized then, the unit will not overheat. I haven't calculated what you would need but, it can be calculated and an auxiliary blower can be purchased and used with the load tester to keep it cool enough for longer testing periods. It's just heat and it needs to be rejected (i.e., pulled out of load tester). Also, you will likely need to modify (increase the size of) the air venting on the unit. Higher CFM (or meters cubed per minute) will require larger exhaust holes. However, there needs to be some back-pressure in the unit so air can enter every square mm (inch) to carry/reject heat. So, if you do this, don't cut the exhaust holes too large. You could always make a variable sized diverter (slider or rotating vane) door or something similar to control the backpressure and airflow. 

2. The only quality variable carbon pile load testers I can find are from Associated Equipment out pf St. Louis, MO. Are there other quality options I should consider?

AutoMeter also has some units. Unfortunately, most equipment manufacturers have moved away from the carbon pile units to electronic units (which I prefer not to use, due to these units not being able to test for all failure modes......and some other things that I won't go into here). Try and purchase a unit that can test 24V systems. This may buy you some extra kW load capacity. It will be more expensive but, a better solution for longevity.

One last thought. If I thought enough schools and businesses would purchase them, I would design and manufacture a programmable load testing unit that would test all DC-DC Converters. We do all of our own hardware and software development for equipment and testing......and this would be a project that would be fairly quick to finish. Your thoughts?

I have the Midtronics GRX-5100 with its massive air cooled resistors, but I cannot see a way to use them on a low voltage system or to make it a variable load.

The Midtronics unit is very inflexible for applications external of the intended purpose and not sure how you would use it for this application.

Hope this helps.........

Mark 

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John from Ogden

 

Educator
 

Hi Mark, 

Thanks for the additional information. I will try the additional cooling fans for now. I am interested in a programmable load tester for DC-DC converters. It cannot be a magic box with a pass or fail (Kent-Moore Tool Style), it would have to produce useful data and be user adjustable with different settings. The cost would need to be lower than $1500 or the school cannot purchase it without going through a Utah state approved vendor.

Have a great day!

John

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Dr. from Port Angeles

 

Engineer
 

John:

You may want to think about using something like a flexible plastic (corrugated) hose to go between the blower and load tester. The hose will need some type of adaptor to the blower so the can be pressurized hose can be pressurized (ditto for the load tester side of the hose). Or, just make an adaptor with no hose??

I did some "back of the envelope" (nothing super scientific) CFM calculations for a 400 amp load. You'll need a minimum of 800 CFM (1000 preferred) to keep the carbon discs/resistors/power transistors cool while testing. So, any holes for the cooling hose will need to be large to eliminate restrictions. At strictly a guess, the hole size for the hose and cut-outs on the load tester enclosure would need to be somewhere between 4.00" - 6.00" (800-1000 CFM is a lot of air to pipe through the load tester).

As for the load tester, everything we would make here would be adjustable and programmable (via software) for the desired load. Not sure the cost could be kept to $1500.00. Even the AutoMeter units are $1500 and there are no programmable features on it. Before I could even attempt to begin this project, there would need to be a minimum pre-order commitment.................which is not likely to happen.

Let me know how it works out, I would be interested.

Best Regards,

Mark

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Jim from Portland

 

Manager
 

Hi John,

Thank you for the excellent study.

I have a challenge for you regarding DC-DC activation strategy on the Honda IMA platform. Here is our story. Well over 10 years ago we were presented with a (not running) Gen 1 Honda Civic Hybrid with a depleted IMA battery (that had been condemned elsewhere), a depleted 12V battery, and a used IMA battery protruding from the trunk. We charged and tested the 12V battery, installed the used IMA battery, and started the car. We observed the IMA system beginning to charge the depleted replacement IMA battery, but the 12V battery was losing its charge. The Civic ICE died when the 12V battery dropped to @ 10.6V. I don't recall the SOC of the IMA battery at that point, but there were very few bars displayed. Exhausting our on-line resources, with the Honda technical site and others, we substituted a known good DC-DC converter and again charged the 12 battery. The 12V battery still wouldn't charge with the ICE running. We decided to support the 12V battery with whatever we were using at that time for a battery stabilizer and hope for the best. At some point (we weren't smart enough at that time to graph output) the IMA SOC reached a critical juncture and the software switched on the DC-DC. Your challenge, should you accept it, is to find out at what IMA SOC does the IMA software switch on the DC-DC functionality?

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John from Ogden

 

Educator
 

Hi Jim,

I know exactly what you are talking about. I probably receive two email or YouTube comments a week from someone with the Honda IMA system, a bad IMA battery, the 12V battery not charging, and the engine stalling while driving. Of course they have already changed the 12V battery and it did not fix it ;). This is a huge problem on pre-2014 Honda IMA hybrid systems. I do not know the exact SOC before the DC-DC converter will work; I think it is a voltage level rather than a SOC. If you put a voltmeter on the battery and rev the engine, the DC-DC converter starts to work around … rpm as the induced voltages from the IMA rotor/stator brings the HV battery voltage up higher. Of course at an idle it quits charging again. The official repair from Honda is to replace the IMA battery and reprogram the battery ECU and the inverter with updated software $$. 

Best wishes,

John …

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