HV Battery Headway 38120HP LiFePo4 70S pack

The "E" fluids were developed especially for battery and motor cooling in the F1, Formula E and other race type vehicles where the battery gets a real hard time. These fluids are non conductive and corrosion/oxidisation preventative with different boiling points designed to rapidly transfer heat without over cooling.

There are some very good adhesive/sealants on the market these days to make this sort of build project within the reach of the competent DIY person .... messing with 240vdc is not something the unskilled or adequately safety aware person should even consider tackling, so anyone actually attempting such a project would already be a skilled worker ....

T1 Terry

 

Is "E" fluids a new way to dissipate heat? I'm sorry I don't know anything about this kind of thing. Is this kind of substance inside the heat pipe in the computer radiator? I searched for news about it. It has advanced technology and is getting more and more applications. Please forgive my ignorance, but I would like to know more about it. Maybe I am more conservative. I always consider the relationship and efficiency of various aspects, how to get the most benefits with the least engineering, and it is meaningful to explore the improvement of prius battery.

 

This is just one of the "E" fluid cooling ideas out there, a lot of player in this new market
https://www.3m.com/3M/en_US/oem-tier-us/applications/propulsion/ev-battery/novec-for-ev-battery/

I did also consider pumping a KOH/distilled water mix through the original NiMh cells as both a coolant method and cleaning the rubbish out of the cells allowing them to be pushed harder without the capacity loss they normally suffer due to the loss of electrolyte.
That leads to the possibility of adding two more NiMh traction battery packs in that space under the floor above the spare tyre, reconfigure the batteries to 2 x 3P9S modules and 1 x 3P10S to make up the 28 modules required.

As far as the motorgenset 1 & 2 in the transmission being strong enough, they are being used as recycled DIY electric vehicle drive units now, seems somone has figured out how to reprogram the computer/inverter to use both motors to produce the torque required and still produce reverse direction drive .... so they are plenty strong enough and certainly last the distance, my ex-taxi Gen 2 now has 736,000km on the clock, still original engine and transaxle ....

T1 Terry

 

3.3v is somewhere between 90% SOC and 50% SOC ..... if the cells hold 3.4v or better over a number of days, then you have achieved full charging and balancing ....

T1 Terry

 

I thought I posted a reply to this, but it must have gone off to the ether or some where. I'll try again.

That is handy info, thank you, roughly 8.29v per module with the original NiMh battery.
That means 6 LTO cells equals one module pair, x 14 prs = 84 LTO cells. 8.29v x 2 = 16.98v / 6 = 2.76v per cell .... so not quite fully charged. 2.85v per cell x 6 cells = 17.1v x 14 module prs = 239.4v ...... either I need to find somewhere to drain that bit of over voltage or not fully charge the cells ..... I wonder how much capacity would be lost under charging the cells by 0.1v per cell?
A Google search seems to suggest the 100% SOC voltage depends on temperature, above 35*C it seems 2.76v would be very close to 100% SOC, but 0% SOC voltage seems to remain around the 1.8v mark, yet 1.9v =0% SOC @ 45*C so I need them hotter to charge than discharge ..... more learning required it seems :lol:

T1 Terry

 

Also take into account that the BMS on the Prius will produce higher and lower voltages than the "full" and "empty" voltages of the NiMH battery. That's because under load the voltage will sag or increase over that point. But once you let off the accelerator or brake pedal it will go back to stand still voltage.

This is a problem that might happen with something that assorbs and discharges the current very well, like ultra capacitors or maybe even LTO cells. The BMS will see the battery is still providing or absorbing a lot of current and could remain at higher or lower than normal voltages thiking the battery is not near full or empty.

 

Are you just trying to make me feel better :lol: When the traction battery was on its last legs in the '06 Prius, I did see 280v as battery voltage on the scan gauge a few time while heavy braking, so there must be a quite a bit of flexibility in the module voltages that carries over into the pack voltage.
The LTO cells will handle 3v per cell short term, so up to 252v without serious damage and as low as 1.5v per cell or 126v ...... I guess I'll find out if the system voltages exceed these to limits. I think I've sorted an active balancing system that can move up to 10 amp if the out of balance reaches the extremes of 1v differential, 1 amp per 0.1v balance differential ........

T1 Terry

 

Famous Toyota Prius Plug-In Conversion Catches Fire, Then Explodes

 

I have several hours of data from my Prius and it does exceed 252v. See here for example Vehiviz

if you go down to the bottom and click on the "VL-Voltage Before Boosted(Volt)" checkbox you will see that its peaking well over 252 for a second or two, repeatedly. Highest was 266 lowest was 202.

Lots more data is here: https://treecricket.com/vehiviz

On this day I got down to 176 volts for a brief moment:

Vehiviz

heres a graph from another day. volt spike above 260 during regen. note Amps are regularly at 60 , i have seen the much higher. this is not crazy driving, this is just toodling around the city at about 35 mph.

 

Dr Prius' "Project Lithium" worked to find a specialty lithium battery supplier, NexPower. if you poke around their website and their posts on here, you can see how they did it.

Each of their modules is basically the size of two original NIMH prismatic battery modules and they are somewhat reminiscent of the shape of the old prismatic. they have lithium inside the plastic housing. I think its pouch batteries.

In their FAQ they have
Max discharge power (< 30sec): 35C or 227.5 Amp
Max discharge power (< 3sec): 40C or 260 Amp

 

That's interesting, even the same colour as mine I at least got the fire out before and actual vehicle damage occurred and well before it got to the point where the house could have gone up in flames.

I know the cause, if that's any help, NiMh module over voltage resulting in one or more cells shorting and igniting the hydrogen/oxygen mix produced by the rapid electrolyser action that occurs when a cell goes over 1.4v ...... in the case of my battery fire, it was only 2 amps and an absolute max of 270vdc, the solar current output is almost zero any higher than that, 7 x 250w solar panels x 38.5v open circuit = 269.5v .... open circuit from a solar panel is at zero current, short circuit current is at zero volts ... just the nature of the beast.

That makes @ Donbright's report of regular 266v peaks a bit scary, even perfectly balanced across all 168 cells is 1.58v per cell, well into the rapid gassing voltage.
The peak on the graph of around 260v coincides with a *regen of 60 amps, the ramp from 220v approx to 260v is rapid showing the cells just couldn't absorb that sort of current rapidly .... maybe tired cells? I assume this is a result of slower than optimal computer sensing and reacting to the voltage spike ....
At least the LTO cells won't suffer that rapid voltage spike, they can handle 10CA or 550 amps per 55Ah cell without rapid voltage change, this will give the computer plenty of time to trim the regen current once the cells are fully charged. These cells have almost ultra capacitor charge and discharge rates, but with a lot more capacity.

T1 Terry

* Actually, very hard to tell which green line indicates the air flow sensor and which indicates the regen amps, so that might be a poor assumption of what is actually happening

 

Sorry, I didn't that you for posting that info, much appreciated.

T1 Terry

 

on the website i linked you can play around with the lines, zoom in, hide the ones you dont want, etc. but yes the spike in voltage is roughly the same moment as the spike in regen. here is a zoom in of a spike. i dont remember if i was on a hill or what but the speed goes from 40 to 0 in about 10 seconds. these batteries are not old, they are NewPriusBatteries cylindricals i installed in 2019.



if you get your own obd dongle (i use a BAFX) and a cellphone with Torque you can gather this type of data yourself and plot graphs in Excel or whatever. i think Dr Prius or one of the other apps lets you make your own graphs too. (these graphs are custom code)

 

Takes a bit to get the head around the graph recording negative HV Bat current on regen, but interesting to see it changing the current in an attempt to control the pack voltage.
After further research using SOC % to cell voltage graphs, I think I'll be doing back to the 90 cell configuration, 95% SOC at 2.5v per cell at a very wide temp range, that leaves a lot more head room for cell over voltage spikes and the low voltage of 176v is still 1.95v per cell, also well within the safe range and leaves the last 5% SOC in the cells .... that still gives me a roughly 50Ah capacity working range and roughly 10kWh of usable capacity, plenty for acceleration assist and room for regen storage, much better than the roughly 1kWh storage in the original Prius traction pack.

T1 Terry

 

The recommended voltage range of lithium iron phosphate batteries is 2.5-3.65v, prius28 series battery packs, according to the calculation of 19.5v each group, the total voltage is 19.5*14, divided by 3.65v requires about 75 lithium iron batteries, also That is, 19.5*14/3.65=74.79, and this number of batteries can meet the needs of a fully charged state.
Let’s take a look at the voltage comparison of the Ni-MH battery when the 75 batteries are dead. 2.5*75/14=.13.39v. I have tested that the lowest voltage of the Ni-MH battery in the car is 12.9v. At this time, the engine starts to charge. The time to start the engine must be higher than this voltage value.
It's just that 75 is not a multiple of 14, and it may be necessary to build a 14-way voltage divider resistor to simulate the detection signal to deceive the ecu. But if you choose a multiple, then only 14*6=84 is the closest, which seems to cause the lithium-iron battery to be dissatisfied, the battery voltage is only 19.5*14/84=3.25v, this voltage seems to be only 30% of the capacity, and it will cause discharge The voltage termination value is lower than 2.5v. Choosing the quantity is very difficult.
If you have to do this work, you can choose the number 75. The advantage is that the charging and discharging interval is similar to the recommended value. The disadvantage is that the voltage divider circuit must be specially made to deceive the ecu, and this will lose the monitoring of the battery balance, and it may need to be balanced regularly. The work of each module voltage.
https://diysolarforum.com/threads/lifepo4-voltage-chart.3156/