2nd gen Honda Insight parallel portable plugin hybrid battery pack build thread

[TimV]

Maybe I missed it, but is it not possible to make a batterie that is permanent in parallel with the IMA batterie? To increase its capacitie and hook up a big charger to charge the total pack?

[RedDevil]

Originally Posted by TimV

Maybe I missed it, but is it not possible to make a batterie that is permanent in parallel with the IMA batterie? To increase its capacitie and hook up a big charger to charge the total pack?

It is possible to do so - I did try, and still can when I remove my lamp shunt and hook up the battery directly.
However, then it will draw a large current when it uses support or EV mode; the IMA system detects that and throws an error.
The voltage fluctuations on the IMA system are quite large, so when matched with a more or less steady voltage pack using LiFePO4 cells large currents will flow.

In practice I can only use a direct connection when I'm on a steady pace on the highway. At lower speeds or when I'm decelerating and pulling away again it will throw an IMA code. When it goes in AutoStop it will throw a code.
I simply do need a current limiter...

Instead of a current limiter I have another idea.
I can use a DC-DC step down converter to feed the 12V system at about 13.8 Volt from one of my 39 Volt boxes so it would relieve the Insights DC-DC converter; as that power does not have to pass through the IMA terminals it enhances the maximal power I can put into my car.

The two remaining boxes each get a DC-DC step up converter to produce 58 Volt, for 116 Volt combined. The current will be limited by the converters capacity to about 10 Ampere (I'm aiming for 600 Watt converters) which should be good.

But before I do so I want to have my meters up and running.
Insight in the voltage and current flowing from my buddy pack to the IMA system is essential.
I've got the stuff and next Tuesday my Insight will go for its annual inspection so I'll remove the harness for the occasion, which makes it easier to work on.

[RedDevil]

The car has had its 80.000 km service two weeks so I had removed the harness as to not cause concern with the mechanics.
And I wanted to tidy up the harness anyway and build and install my volt- and ampere meters for the hybrid battery, plus the diodes.

As luck would have it conditions have been fair, more than compensating for the lack of PHEV support. Which was mild anyway, but I do see a lot more of recharge on the go now.
Thanks to the relay in the lamp shunt (switching between a 6P and a 2S3P setup for the 12V lamps when the current gets too strong) the forced recharge on the go is all but gone, except for the occasional recalibration, cold start or after a long stint of EV use. Even so, it uses about 300 Watt on average, judging by the recharge time of the batteries.

I have soldered in the power and sensor wires, a pesky job as the solder refuses to bond with the on-print contacts if it gets half the chance. And when it was done one of my meters had a failing segment..
But I had a spare one, the one I blew up on my first attempt when I did not realize the power feed had to be isolated from the sensor wires as they share a common 'ground' (actually the power + is connected to the sensor -, weird... but it works).
I took the blown and the faulty ones apart and swapped the LCD display, and hey presto it works! My first LCD meter hack

I will feed the meters by a 9 volt battery, switched by a micro relay fed by the 12 V keyed system. I got some parts here, after testing:



The meters will go to a box somewhere in the dash area, obviously, which means bringing 100 Volts into the passenger compartment.
But I'll put 100 kOhm resistors on the negative wire and a 10 MOhm one on the positive one; if the wires would short with the car or amongst each other, it would still dissipate no more than a milliampere or some 100 milliWatt over that resistor.
I calibrated the Volt meter to compensate for the extra resistors.

This will not bring more support yet, but at least I'll know what's happening better than I do now.

This is not the fastest of builds... but I am confident I'll get there in the end, or at least somewhere.

[RedDevil]

I'd like to add that I have had no IMA errors during my last month of PHEV usage.

Those, it seems, are mainly caused by having a load on the terminals on key-on.
Making sure the (relayed) harness is switched off when I start the engine is enough to prevent it. And of course, the relay lamp shunt allows for a 10 Ampere feed maximum.

One tiny problem is that the number 2 cell in my number 2 pack is lagging a bit.
When I charge the batteries that cell trips the BMS because it is full earlier than the rest.
The BMS will top balance it in line, but that is a very slow process.
Then, it is not a lot off. If I drain the overcharge at about 300 milliAmp a few minutes is all it takes to make it match the others (all cells at about 3.65 Volt on charger cutoff).

It could be the cell or the BMS.
Next time after balancing I'll swap the no.1 and 2 cells on that battery, and see whether the problem swaps position too. I hope it is the cell, much cheaper to replace than the BMS!