Prius Grid Charger/Discharger with Electronic Load

Thanks to all the other members in the DIY Grid Charger threads, I just finished building mine. I thought I should share my version, since it uses an Electronic Load, which I haven't seen in any other build.

Build log is in this thread. Schematic attached below.
What type of connector does a Prolong Charger/Discharger use? | PriusChat

Why an Electronic Load?
1. These devices are designed to test batteries, so it allows you to precisely program the discharge curve, including current, voltage, power, time, displays all these values while discharging, as well as a voltage curve at the end of the cycle.
2. Built like a tank. It discharges via a bank of power MOSFETs, bolted on to a tunnel heat sink that runs the length of the device, all cooled by a temperature controlled fan. I checked the temperature periodically while discharging, and it never exceeded 95F. It also has extensive protection settings for over current, power, voltage, etc.
3. Since it has a built in volt/amp meter, it simplifies the build considerable. These 3 cables are all I had to build.

4. It will work for more than a Prius. Just program the desired termination voltage and current to suit your vehicle.
5. They are programmable, so you can connect your computer to automate the whole process, text you on each step, graph out the voltage curve, or anything else you can think of.
6. You can use it for a lot more than reconditioning your battery every few months, especially if you do any sort of electronics repair.

So why not?
Well, these are > $1500 brand new. But... you can get used lab equipment for cheap on fleabay if you are patient. I got mine from the Lecroy Outlet Store for $375. It was brand new, just an older model. I've seen other Electronic Loads pop up for < $400 periodically. Not quite a $100 DIY Grid Charger, but for < $500 total, it's a lot cheaper than some of the commercial offerings.

And best of all, no more swapping light bulbs and monitoring the discharge voltage like a hawk!

 

1. Only 115k. I live in Hawaii now. I can only drive around the island that many times
2. Got the P0A80 code. Dealer quoted $6k+ to replace the battery (again, in Hawaii, there is only one dealership/service center that has a monopoly). Priuschat led me to Prolong chargers, and @PriusCamper led me to the DIY grid charger threads.
3. 11% increase is not bad, I just needed to temper my expectation given that I have a 13 year old battery and I waited till I got a P0A80 code before reconditioning. It works best if your battery is still in decent condition. My out-of-pocket expense for this build is < $100, since I already had the Electronic Load and Bench Supply. So it’s definitely worth it for me if I get another year out of this car, given how expensive and unavailable cars are right now. For you, it will depend on what condition your car is, and how much longer you plan to keep it. The first step I would do is run a battery test with Dr Prius or Torque, as that’s really cheap, and teaches you a lot about your HV battery. Then the normal $100 Grid Charger project (instead of this $500 one) is a very small investment if you do decide to recondition your battery.

 

@Tombukt2 The charging part is still a Meanwell 350mA CC supply, that can output 143-286VDC.

The Electronic Load itself does not output anything. It just lets you program very precisely how you want to discharge the battery. Specs on the particular model I have (a rebadged PEL-3032E) can handle max of 300W, 0-500VDC, 0-1.5ADC. I'm discharging at constant resistance of 400Ohm. At max of 240V, it's just 0.6A, or 144W, well within it's specs.

 

It seems that there are a bunch of cheaper electronic loads available since I last looked, so you do not have to go the fleabay route. I did a quick search and found 2 that have decent reviews, with tear downs.

Array 3711A 0-360V 300W, by Kerry Wong
Beich CH9720CU 0-360V 300W, by Chris Grossman

A quick search in aliexpress show that they are about $375 + $75 shipping, about the same price range as my build.
There is also the Array 3710A (150W) and Beich CH9720B (150W and no USB recording) for about $275 + $75, so we could possibly shave another $100 off the build.

I think electronic loads solve a lot of the problems with the finicky discharge termination in DIY grid chargers/dischargers, so it's definitely worth moving towards, if we can get the price down.

 

Just a quick follow up.

I finally bit the bullet and replaced 3 bad modules and Dr Prius now says that the battery is in good condition , 79.53% (up from poor, 40%). It’s been working fine now for several months, so yet another data point for anyone who tried a grid charger but still had battery issues.

I was really hoping to make my Prius last a couple more years until cars were readily available to purchase again, but guess what? I just got a call this weekend from the Toyota dealership, so I’ll be picking up a 2023 Prius Prime tomorrow. I believe I’ll be the the first in my state of Hawaii to get one.

So I’m currently ripping out the harness as I don’t want the next owner to get hurt messing with a strange cable under the trunk.

A big thank you to all the fellow members who helped me. A little sad leaving this forum. I was all ready to do an EGR cleaning and catch can next. Maybe I can start a new thread on preventive battery maintenance in the gen 5 forum, but I think that’ll need to wait until enough people in Priuschat get their hands on one.

 

Fortunately, I’m on a Ohau (different island, so no chance of the fire spreading across the ocean). That said, a clinic from my company burned down, some friends lost their homes, but fortunately they are safe.

 

The ETS5411A+ should work. The key spec is the 500V rating, as the HV battery could be 250V+ when fully charged. The current rating of 15A is also fine.

There are a few reviews on the web you can read on it. From what I can tell, it’s probably the cheapest electronic load you can get that works. Downsides are the build quality, unintuitive UI, and some reports that certain modes do not work properly.

That said, I think that it’s much better than jury rigging light bulbs together and swapping them to get the correct load.

If you can wait for shipping from China, the ones I listed in the 1st post are much better quality for about the same price. There is really no substitute for mass (of the heat sinks), and those are much bigger and heavier units.