Lithium install connect to prius side of terminals instead of HV OEM battery side?!

The inverter will see the potential, but it won't do anything with it. It would be like having an appliance plugged in but turned off. This won't harm the inverter, but it does create a potentially dangerous situation where the lithium battery is no longer isolated if contactors have failed. For example, in a car accident, you would have live conductors.

The Enginer system connects as you show, to the red-circled posts. There, the safety is that the Enginer DC converter will not operate if the car is not in Ready.

 

Both approaches carry some risk. If you connect to the battery side of the relays (green), then the lines running from there to your contactors are always live. If you connect to the frame wire side (red), then the risk comes if you have a contactor failure (such as, you have an accident that causes them to stick). The risks in either case are small and there are tradeoffs.

 

I guess the one thing I wonder, how will your lithium packs overcharge the Prius NiMH pack? Are they over 260V?

 

If Lithium == LiFePO4, that you charge to 3,65V/cell, which later falls to 3,35V/cell after surface charge dissipation, for 241,2V in your pack. Then there will be an additional voltage drop when the Lithium packs "sees" the NiMH pack. The Enginer people normally run at 235-240V. I do not see you having a problem with overcharging the NiMH pack in the case of contactor failure.

Next, in your latest picture, by passing one of the wires through the current sensor, it will cause SoC errors, unless you replace the battery ECU. Is that what you mean by Plus?

 

Okay, I thought you were talking about BMS+

So, let's go back a little.

241,2V is the most that your LiFePO4 pack could provide, in the case of stuck contactors. This is 1,436V per NiMH cell, assuming no voltage drop. This is about 100% SoC. It is not something that you want to do all the time, but it is not a catastrophe.

With the current sensor, you have two problems. If you bypass it, then at >14A current, you will get a DTC, as you say. If you pass your wire through it, as shown in your picture, then the Coulomb counting algorithm in the battery ECU will calculate that the battery is being drained faster than is actual, and you will drop out of EV mode too soon. So you need either a custom battery ECU, or you need to spoof SoC, but I think with spoofing, you get a negative recal (forced charge of the battery by the ICE) when you shut things down. I believe BMS+ (now BMS2) solves this problem. You may wish to contact the designer, it is well worth the money if it works.

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If you connect directly to the OEM terminal side (no current sensor bypass). The OEM battery ECU will count down coulombs via the hall effect current sensor and adjust SoC accordingly and it assumes that the OEM HV battery pack full capacity is 6.5ah and as SoC nears 40% the Hybrid ECU will call for the ICE to come on aggressively to charge a HV battery which is supposedly on low charge. The OEM battery ECU does not know that you have a 20ah lifepo4 connected in parallel and never will. This is where using a BMSplus to fake the SoC is needed.

The current sensor bypass is needed to avoid a DTC for high battery current mismatch. The Hybrid ECU compares currents it measures/calculates against current reported by the battery ECU and will throw a DTC if difference in current is generally greater than 16/19 amps. This DTC is known to disable the ICE and stall the Prius and thus putting the driver at a high risk of causing an accident.

Both the SoC spoofing device and the current sensor bypass are critical for the use of any added HV battery packs in parallel on a Gen2 Prius.

 

That is a wise approach. When the vehicle is off by the driver or in an accident, the relays will open and there is no close loop for the PHEV pack going to the OEM traction battery nor the OEM inverter.

Great idea!!!

 

Kudos for Flying White Dutchman .:cheer2:
So F.W.D. deserves a brand new Enginer Kit as a reward. Hurray !!
Not to mention that I have been using the same connection approach since my first DIY PHEV conversion on December 2006 and rolling 'til today.

 

Kudos for Flying White Dutchman .:cheer2:
So F.W.D. deserves a brand new Enginer Kit as a reward. Hurray !!
Not to mention that I have been using the same connection approach since my first DIY PHEV conversion on December 2006 and rolling 'til today.

 

This is a link to how to do the Hall Effect Current sensor bypass:



Prius PHEV Schematics - EAA-PHEV

It was interesting to see that a Battery Tap Emulator - EAA-PHEV battery tap emulator was used before the BMSplus was available. This battery tap emulator could be used to fool the battery ECU so that the OEM NiMH battery could be removed. Then you could replace the OEM battery with a Lifepo4 HV battery. Most of the electronics is not needed as the BMSplus already does the spoofing so the 14 resistor//capacitor voltage divider is all that is needed to fool the battery ECU to think that there is a NiMH battery pack connected.

When you consider that the effective SoC that can be used for a NiMH pack is 40% (2.6ah) and it has a high self-discharge/heating and has a low power density it makes sense to ditch the old OEM NiMH HV battery pack and replace it with a Lifepo4 pack.

The NiMH pack has a o/c voltage of 191v at SoC of 40% which would correspond with a Lifepo4 cell voltage of 191v/72cells=2.65v.

The NiMH pack has a o/c voltage of 242v at SoC of 80% which would correspond with a Lifepo4 cell voltage of 242v/72cells=3.36v. The Lifepo4 pack has a charged resting voltage of 3.35vx72cells=241.2v which is close.

Obviously the rate of change of voltage on a NiMH battery is a lot faster than the Lifepo4 which would probably confuse the OEM battery ECU causing it to throw a DTC. Obviously that by removing the original NiMH battery pack that you no longer need a Hall Effect Current Sensor bypass or the HV battery fan assembly which takes up a lot of valuable battery space and weight.

 

Has anyone tried partially bypassing the battery curent sensor and the inverter current sensor ? So that it doesn't seem a mid match ? Won't this also bang more current into the mg1 and 2 and also regen with more current I to the battery ,?