[RedDevil]

Hooking up my batteries with the IMA system did result in IMA errors. But what if I use a shunt?

First run - single filament lamp
I hooked up a 55W H7 lamp in series this time.
My pack voltage is at exactly 120 Volt now. Each battery at 40.0 Volt, apparently perfectly balanced. Just like it was after last test.

When I hooked it up without the shunt the voltage dropped to 109 Volt, and it threw a code.
With the light in series, when I flip the switch...
It burns quite bright, not full strength but still impressive. And the voltage on my pack drops to a whopping 118.5 Volt; just 1.5 less!

I guess it burns away at over 3 Ampere so the total internal resistance of my pack must be less than 0.5 Ohm!
Way less than my 0.8 Ohm estimate. So the current was much higher than I expected.
No wonder it threw codes!

Light still shining, no codes whatever, I start the engine. The lamp shines really bright now; it is taking on charge at speed. But it recedes quickly once on the move.

It is quite easy to provoke and sustain EV mode, which makes the IMA voltage drop and the lamp shine white bright. Once it re-enters gas mode the light dies and it even says on the dash that it is recharging the IMA battery.
Meanwhile, for the first time in all my testing, the trip fuel consumption is getting lower than would be possible without the pack. It is doing something. And it is getting better all the time.

Out on the open road, I accelerate gently to 60 km/h. Upon stabilizing the speed it goes into EV mode, which otherwise rarely happens on the level. The light shines bright - too bright. It blows.
The IMA battery, that was taken somewhat above its usual SOC, keeps the FE good for a while. Then it all gets back to normal again.

Second run - double parallel filament lamp
Back home I figure one lamp may reduce the current too much. I also have a twin beam 55/60 Watt lamp. I hook it up in parallel so it could accept double the current.
Hopefully the higher current will reduce the voltage difference so these won't blow.

I flip the switch again with contact on, engine off. PING Check IMA system.
Okay, so this was too much.
But it should work with the engine running.
Reset the code, start the engine, flip the switch.
It runs fine, lamp shines bright. Again I can provoke EV mode with ease.
Fuel economy starts to rise again, leaving common read values behind.

Then PING Check oil system.
Ah, we know that; Honda's way of teasing you one mile after a IMA code reset. Key off and on while on the move, that should clear it. On key on the lamp in the back flashes bright and fails. And the system throws a Check IMA system message to boot. Oh joy!
I limp back home, reset the code and remove the lamp and batteries.

Conclusion
It is a success, at least it showed that one lamp is all it takes to prevent IMA errors. But I need to put 2 in series as it would go bust if the IMA system gets exercised. And I have been burning though my stack of wrongly typed halogens at speed.

And I need a new control box. Because the old lamp box is starting to fall apart, it is not sturdy enough after all.

I want that lamp but I also want to be able to switch it out of the system when I'm on the motorway doing a steady speed. I bet it won't be needed anyway once the pack voltage drops on discharge to below 117 Volt or so.

So I need to route a 3 way switch to my drivers position, and probably a volt and possibly ampere meter too. I'll solder in some high ohm resistors on the high voltage lines to the meter so a short would just cause a tiny current. The meters should not take much current anyway (the ampere meter shunt stays in the back of course).

I'm confident I can make this work now.