HV Pack Voltages & Grid Charging

Howdy folks!

I'm an Gen 1 Insight driver myself, and put together a plug-in charger for my car a little while ago (based on instruction from Mike Dabrowski at 99MPG.com), and I'm now helping out others by putting together kits while I'm currently unemployed.

I made a new friend in the process who is interested in improving upon it, and also applying it to the Prius. So I'm wondering if someone has already done this, and if so, where can I find the information?

The first thing I need to know is the maximum voltage expected from the battery. In my case, I have 120 1.2v NiMH batteries that generally provide at max of around 170v. By that math, your 168 1.2v NiMH batteries should produce a max around 235v. However, I'm a bit confused, because phev.org states that the maximum voltage is 302v, which is much higher!

Would someone mind clearing that up for me? Maybe I'm missing a gap of knowledge in the technology differences.

Next, could you guys please confirm that the best connection points are directly to the battery? On my car, we connect to a large precharge resistor that is before the positive terminal, but I see that the Enginer kit connects directly to your HV battery terminals. Also, do you happen to have the size/type of terminals that are required to connect there?

Finally, I'd want to make sure to get power to the stock battery pack fan while charging. On my car it's a simple 12v connection that we splice in. Is that possible on the Pruis, or is there a more complicated solution?

Anyhow, for my car, the design is simple - three 48v constant voltage supplies in series with a constant current power supply to regulate the current in, and then a 12v power supply to run the pack fan (and in my case, a fan on the charger itself).

Any help on this topic is appreciated, including links to other projects, resources, etc.

If you'd like to see more about what I'm putting together, you can check out my thread by visiting my redirect at hybridgridcharger.com. Please disregard the drama...

[I can't post any direct links as this is my first post, sorry about that].

Thanks in advance for your help!

Charging the Prius battery is not recommended. It will shorten the battery life. The Prius system tries to keep the battery between 30 and 80% charge. Going lower will increase the risk of reverse charging a cell and going higher will increase the risk of overcharging a cell and causing venting. Either event will be fatal to that cell.

As for your questions:
There are 168 cells in the Prius battery. The inverter bumps the (nominal) 201V to the 350V range and outputs three phase AC to run the motors and rectifies and converts it back down during regen.
NiMH cell charging voltage is higher than 1.2V/cell, closer to 1.5V/cell. Cell voltage is nominal 1.25V charged but you need more to drive the required current into the cell.
You need temperature monitoring capability so your charge cutoff can work. There are several thermistors in the pack you could use, if your circuit can share them with the Prius system.

-I- wouldn't try this with Pearl, but do whatever you think you can get away with!

I understand the concerns with over-charging. We're essentially using the same technology in our battery packs, and stock, we also don't charge 100%. We use these small chargers to balance our battery packs and bring everything up to 100% every now and then, because over time, cells get out of balance and limit your overall usable capacity.

You're right about sensing heat, but also, you can detect the state of charge by voltage approximately. And in the case of the Prius, it outputs some nifty SOC numbers that could be used if we gave power to the right component (which we don't get on the Insight).

Thanks for the info on how the output works. I didn't realize that your voltage was upconverted to drive an AC motor. Very, very interesting! I have so much to learn!

The Prius traction battery has a nominal voltage of 201.6V but the actual voltage is more like 230V-240V. The voltage is converted to ~500VAC by the inverter. The use of this higher voltage (and corresponding lower amperage) reduces power losses.

I am an electrical engineer & Prius Gen II owner. I have been working on a charger, but at 5 amps, not 350 ma. The Prius battery is a lot larger then the Insight. It is 5.2 KWH, so at 350 ma @240 v, that is 84 WH, so it would take 62 hours to charge. Mine would take 4.3 hours.
I'm not so sure what you are trying to do is realistic for a Prius. FYI, the electric motor in the Prius is 68 HP, in the Insight, I think it is 15 HP.

The normal Prius battery is 6.5AH with 168 cells giving about 1.3KWH.

Five Amps for 4 Hours would drastically overcharge it and probably cause it to burst.

kevin

Welcome Artric!

Charging to 245V on a Gen II (2004-2009) is probably what you need. This is normally the highest set point for an Enginer kit. This way, the SoC will stay below 80%, more like somewhere in the 70-75% range. The Prius gets VERY unhappy if SoC nears 80%, and will spin the ICE to draw off the excess battery charge. There is no problems with imbalance either, so there is no good reason to charge over 80% SoC

The Enginer kit connects downstream of the contactor. The contactor is only closed when the car is in READY mode. You will need to connect upstream of the contactor since the current drain on the battery is at least 1 amp to power the car in READY mode when the ICE is off. If you want to connect the charger upstream of the contactor, then you need some way of protecting your connection against a short in case of an accident, maybe a separate contactor or relay that is only closed when your charger is connected.

The HV ECU is a CAN bus device. Having it tell you the SoC while you are charging would be way to complicated and expensive. Best bet is to have the voltage cutoff at 245V

BTW, Vertex, you can charge at 5 amps, just make sure that you have a separate circuit that is running the HV battery fan.

All caveats aside, there is a small potential market for a Prius grid charger, especially people like me who have a Gen 1 Insight as well as a Gen II Prius with a plug-in kit. Enginer makes no provision to charge the traction battery when the car is turned off, but it sure would be nice to have 7 bars when starting off in EV mode.

Hi Seilerts,

I'd suggest you start the car 10 minutes before you need to leave, and then power cycle the enginer charger. the enginer kit will bring you up to 7 bars, and the charger will happily put that power back into the enginer batteries while the car is running...

Thanks very much, this is what I thought. I really hope that he is talking about something else if he is an electrical engineer! Maybe it was a joke, or sabotage from those out to get me at the other forum?

Thanks so much for the info! It sounds like you've given me exactly what I need to know! It's funny that the car will work so hard to see that you don't charge over 80%!

Good advice about connection to the battery - I'll look right into that!

Ah, so you're a Gen 1 Insight Owner as well? Cheers! If you're interested, once we have everything together, we could potentially make the charger applicable to both cars - either manually or programmatically turning off unneeded power supplies when you charge the Insight.

Do you happen to know anything about connecting to the fan on the Prius pack? I would prefer to run it at all times when charging, just to be as safe as possible. Would just a standard 12v spliced in work OK like it does on the Insight, or do special considerations need to be made?

All the best,

Art

Sorry, late night oil. The number I gave is for 4 batteries in parallel, I forgot to divide by 4. So, it would be 15 hours vs 1.1 hours.

Ah, I see what you are saying now vertex. You probably don't need to worry about cooling. Artric, at 350 mA, you definitely don't need to worry about cooling. Also, at least for the traction battery, it would be unusual to charge more than 35% of 6.5 Ah, given that the computer won't let SOC go below 40%, and the target SOC is around 75%.

Flanina, what I usually do is leave the car+pack on for a few minutes when I get home. I just think it is a PITA. Note that the Enginer pack may be putting out 70 amps to run the converter, while the charger is only capable of 15 amps...and I don't know if running the charger and converter at the same time would cause a problem for the BMS.

I admit, a grid charger for my PHEV Prius is an extra bit shiny chrome for the nerd-mobile. My own plan is to have a traction battery charger run at the same time as the engine block heater and be on a two hour timer.

Seilerts, Seems like charging the traction battery is overkill with a Enginer System. Actually, for just the 1 traction battery, 1 to 2 amps is enough for me, since I would typically charge overnight. I have a second battery I was going to add in parallel, but my calculations show that even with 4 batteries, I could not get enough range to drive the 2.2 miles home from the train as I orignially wanted to, since it has a lot of steep hills. Once the ICE has to turn on, the point of all those batteries becomes mute.

Have you tried running segments in EV mode with your AutoEnginuity, recording SoC, voltage, and current to see what is required? It's hard to see how you couldn't make it with 4 grid charged traction batteries in parallel -- that would give you around 6 amp hours to play with (1.5 ah per). A conservative estimate for range in EV mode is 1 amp hour per mile for flat ground at 30 mph. You would have a budget of over 2.5 amp hours per mile with 4 batteries???

I hadn't really thought of that. What I did do was start in EV mode at the bottom of the hill, which is 1/2 mile, steep (7%) grade. With the SOC showing green, I get 2 blocks in EV mode, and I am down to purple with the single traction battery. I would then mostly deplete all 4 batteries going the 0.5 miles. Then I have to drive 1.5 miles which is flat to a few degree uphill grade, to another hill, which is 10% grade, but only 0.2 miles. Of course, I can leave my house to get there in EV mode, and end up with more charge then when I left.
Now, if I dig into the battery controller, and modify it, so that I can use 80% of the battery range, and use 3 or 4 batteries, then I should be able to do it. Of course the battery life will suffer.

Kietyyyy was talking about making available a SoC spoofer, I don't know where that's at though. As far as battery life goes, these things are over-engineered, and junkyards are overflowing with Gen II batteries, so it is more a question of making sure that you always have enough left to start the traction battery. Your application is interesting.

Spoofing. I understand that if you monitor the bus, and send a second SOC right after the first, the system will ignore the first, and think the second spoofed one is correct. I will have to keep that in mind.

Once you get this "battery" bug, it's an expensive and time-consuming disease!

I've built a 7.2kwh A123 Lithium-Ion pack to outright replace the Toyota pack in my '08. Now I'm working on a new Battery ECU from scratch to replace Toyota's. It will allow much better control of what's going on battery<-->Hybrid System wise. I hope to include full 52mph mode and eventually warp-EV mode at up to 70mph. (this is like warp-stealth where the Engine still spins, but with no fuel or pumping loss)

There will be no need to spoof, as I can make my ECU present whatever parameters are needed over the CAN bus, and only those.

It is variable speed using PWM technology.
http://www.autoshop101.com/forms/Hybrid03.pdf

Ken@Japan

Wow! Please post more details (in a new thread maybe) when it's up and running. Good luck!