DIY High Voltage Battery Reconditioner - Grid Charger

Thank you for the amazing write up! The only bit I'm not sure of (no real electrical background outside of home wiring) is the resistor close to the power supply. This is to soak up current from the battery after the power supply is turned off right? Is it wired across the positive and negative leads of the power supply making a circuit? I will have the diodes after this so hopefully that protects the battery pack from feeding back into the power supply (I think) but if that is the case I'm not sure the role of the resistor and with the wiring something between positive and negative leads I'm worried about a short if I'm understanding the schematic wrong.

 

Excellent post great job designing this. I have a 2011 CT200h which is a Gen 3 prius that just started getting the P0A80 Replace hybrid battery pack and techstream shows 4 cells with lower voltage.
But... I priced out the materials on your BOM, in today's price (2024) and they come out to almost $300 + tax using your same sources and identical items.
Instead I bought the premade maxx volts charger for $369 with no tax. For discharging I am going to still use the lightbulb method.

 

Here's some info on new tools I suspect may be VERY handy for grid charging/discharging... and individual module analysis as well:

1) TestController is a wonderful tool for managing a wide variety of smart instruments: meters, scopes, loads, power supplies, etc. See Program that can log from many multimeters. - Page 1
2) There's some pretty amazing digital load devices out there these days. I just picked up a DL24MP load at aliexpress. Claims to handle 150W, practically speaking 100W should be no problem. One cool thing: up to four of these can be connected to handle up to 600W (reality: 400). A 450W unit would be under $70. This is a smart device, computer controllable via blue tooth. Each unit has four high power MOSFETs for handling the load.
3) Do you need to cool high power resistors? Pick up some pure mineral oil... cheap at Walmart, Sally Beauty, or any Ranch hardware store. Nonconductive and cools just fine

 

I really liked this idea at first. Slowing the discharge as the pack voltage nears minimum (6x28=168 volts in a Gen2) is very good since it falls faster late in the cycle. But I think there are a couple issues.

I read at the bottom of the aliexpress page how the power rating must be reduced proportionally as you slide the tap down from full resistance. Because the heat dissipates over a shorter portion of the tube. They also suggest if you want to run it longer than 10 minutes you reduce the power rating by 2-3. I think that's what they're saying, language barrier is high. Also I feel as if a hot glowing light bulb is safer than a hot not-glowing resistor. If only because my lizard brain is trained to be cautious with lit lightbulbs.

I wonder how much the power could be increased with a fan blowing across it?

 

There are reasons why we use a light bulbs instead of resistors in DIY grid chargers/dischargers. It's dirt cheap. Sockets are also cheap, readily available, and easy to hook up without specialized equipment. It's available with many wattages, depending on your needs. It's self regulating since the resistance increases as it heats up. It fails open, so it automatically disconnects. It's designed to dissipate heat without burning up. It provides a visual indication of state of the discharge. Main disadvantage is that you need to monitor your discharge voltage carefully so you don't over discharge.

Resistors need to be hooked up in parallel to provide the necessary wattage. You need to provide cooling (heat sinks, fans, etc) to get the rated wattage. That said, commercial units like Prolong uses a bank of them, since it's simple to control the discharge curve with a microcontroller and relays.

Best would be to use MOSFET based electronic loads. It already has the heat sinks and fans for its rated load, and the programmability to stop the discharge at your set voltage. Disadvantage is the cost, but the price keeps dropping, and you can get them pretty reasonably from Aliexpress nowadays. This was what I used for my build, documented in another thread:
Prius Grid Charger/Discharger with Electronic Load | PriusChat
What type of connector does a Prolong Charger/Discharger use? | PriusChat

 

A couple of days ago my 2012 Prius triggered the P0A80 code. I think it is time for me to build a grid charger by utilizing tetech's design as much as possible. However, since my knowledge on EE is limited to my high school physics, there are a few questions I hope tetech or someone here can help me:

1. LPC-100-350 output voltage (286V) is higher than the Gen 3 traction battery's saturation voltage, is there any precaution I should know?
2. The LED driver's constant current region is 143 - 286 V. What amperage does it supply when the battery voltage is lower than 143V? Will that be a problem?
3. Looking at tetech's circuit it is clear the voltmeter/current-meter will measure the charging voltage and current, but does it also measure the discharging current? I am not asking the discharging voltage because it is clear the voltage is measured.
4. How crucial is it to have the bleed resistor?
5. It looks to me that only J7 is grounded with J8 plug. All other wires/connections are un-grounded. How come all the connectors and sockets in the parts section are 3-prong type? Will 2-prong work?

Thank you in advance for your help.

 

Just to make sure you know, a grid charger will NOT fix a hybrid battery that already has the P0A80 trouble code.

 

Very well done schematic and presentation especially the safety information. I might build one of these, though I don't know if it's worth it or not on my 2010 with 175K miles. I haven't gotten any codes yet, but I know I have very little battery capacity left. Will it gain me a year on the batttery potentially? or is it a guaranteed waste of time with the age of my battery?

 

Thanks. Then what could be the cause of the P0A80?

After clearing the code yesterday, the car passed Dr. Prius' "Full Battery Test". But the "Life Expentancy Test" only yielded 56%. I drove the car for 130+ miles at 75 MPH in 100F weather. The car showed no issue, and the MPG was 55+.

 

The P0A80 code is triggered when the voltage difference between the battery blocks is too high. Usually, this is because one or more of the battery modules is going bad, or the battery pack is out of balance.

Let's discuss this in one of the treads you created for your battery problem.

 

1. The LPC-100-350 supplies a constant current of 350mA, and the voltage will be whatever the battery is. The 286V rating is just the maximum output voltage it can generate. The current will will drop once the load hits it's maximum of 286V.
2. If the output voltage drops below 143V, the power supply will think the load is shorted, and will shutdown for a few seconds, before trying to power the load again. This is called the 'hiccup' mode in the specs. If you hook up a voltmeter, you'd see the voltage go up and down and up and down. See my experience at What type of connector does a Prolong Charger/Discharger use? | PriusChat
3. No, it does not measure the discharging current. To measure the current, it needs to flow through the ammeter. This is rather difficult to route via switches, and your best bet is to hook up a separate ammeter.
4. The bleeder resister is to quickly discharge the capacitors of the power supply when it is turned off. This is for safety, as it can take 60 seconds or more, where there is still hundreds of Volts at the output. The resistor itself is only a couple of bucks, so no reason to skimp on this.
5. The circuit itself does not need ground, but ground should be connected to anything that could be live when there is a short (like the metal chassis, even though it's not shown in the schematics). I think the OP used a 3 prong discharger socket because 2 prong connectors are more expensive, harder to find, and generally lower quality. Ground is not connected on the discharger socket because it doesn't do anything, as the Prius battery is not grounded. Feel free to substitute a 2 prong socket there. But be very careful constructing the lamp discharger as it could be up to 250V, so make sure there is no exposed metal parts.

Hope this helps @PriusII&C, feel free to ask if you still have any more questions.

 

Thank you @CatNinja. The thread you referenced has a lot of great information.

I did order some resistors a couple of days ago, but I picked up 500k resistors instead because I want to minimize heat produced by the resistor during normal charge process. I don't know the voltage decay rate during the bleeding process. Assume it is exponential, this will probably increase the time constant by a factor of 3 - 4, compared with the 150k Ohm in @tgtech. Hope this is fast enough. If you have some idea, please share.

Originally I planned to recondition the battery in the car in my garage. This way I will avoid to lift and remove the heavy battery pack from the car. But looking at your experience, the Mean Well Driver and the battery pack will be 10s degree or more hotter than the ambient temperature. These days inside my garage in the afternoon the temperature routely reaches 90+ easily. It probably is a good idea to remove the battery and take it inside to do the reconditioning, even that means more hard work

 

@PriusII&C Taking the battery out is a LOT of work. The whole point of the grid charger/conditioner is that after you install the harness, it’s just a couple of wires sticking out that you can plug into every few months to rebalance the cells.

If you have the battery out already, you might as well test each cell and replace the weak ones. That was what I ended up doing anyway because reconditioning only worked for a few months. It’s been error free for 3 years and counting after I replaced 5 modules.

Why can’t you just pause the process during the hottest part of the day?

 

Definitely I'd like to leave the battery in the car for the reconditioning.

I have the impression that pausing in NiMH battery reconditioning is not good, but forget where I got that idea. Maybe I mix it up with something.

 

There are 2 parts to reconditioning.

First is to set all modules to the same state of charge. P0A80 code is thrown when the delta between the modules is more than 0.3V for more than a few minutes. This can happen easily if some modules are more charged than others. The easiest way to do this is to ‘overcharge’ the battery so all modules are at 100%. Normally, this is not recommended because any excess charge is dumped as heat. And heat is what kills batteries. But this can be managed by doing it at the trickle charge rate of C/20 (325mA), which is what the grid charger does.

The 2nd part is to fully charge and discharge the modules multiple times. This may help cells that have reduced capacity recover some of it.

Certain chemistries like LiIon do not like being fully discharged for long periods, so you should avoid pausing during that step. But this is not an issue for NiMH.

If you understand what we are trying to do above, you’d see that pausing would not cause an issue.

BTW, if you haven’t bought all the parts for this build yet, you may want to consider my build instead. More expensive, but much easier. Just 3 wires. Schematic here Prius Grid Charger/Discharger with Electronic Load | PriusChat