Question about 12 Volt "starter" Battery (Please move if incorrect)

[muehlpower]

So on an over current event, it will "cut the power" like a resettable fuse.

I am aware of this, which is why I want to measure the current running into the 12V battery and reduce the DCDC converter accordingly. The DCDC then produces a maximum of as much current as the battery can handle plus the current consumption of the switched-on devices. Sounds complicated, but it's actually quite simple. Measure the current to the battery, reduce the voltage at the DCDC until the current to the battery is below the desired value. The upper limit for the DCDC is the maximum voltage of the battery. For my battery 42A and 14.6V. However, I will set 30A and 14V. To be safe when discharging, I install an 80A fuse.
I will use a IBS 200 X sensor from Hella to measure the current.

[DVD3500]

*snip*
Regarding heating, there is some good work being done on HV coolant heaters. That way you can keep the spitfire heater core.

Out of interest what battery, motor and charger set up do you have? You say you kept the flywheel and clutch as you are using the getriebe still. Most people still remove these, so if you are looking at cutting down the weight I would start there. Those old iron flywheels and old style clutches on the spitfire are really heavy. You would also notice an improvement in acceleration too.

Thanks for the clarification on the battery!

That would mean though trying to find space under the hood/bonnet for the coolant heat. The conversion I have already seen really fills up that space and unless it is the size of a packet of cigarettes I don|t think I can get it to fit.
There there is routing the hoses etc. I am not saying it is impossible but I am thinking for the amount of time and level of heat I need PTC elements and some wiring might be easier. The coolant heater needs to get everything up to temperature (oh how I hated that in my diesel cars...) too and for the short jaunts this car would likely do maybe not an ideal solution.

Leaving the transmission/gearbox in means one less thing for the TÜV to check. Also the differentials in these cars are not used to a lot of torque so feeding that through the standard transmission should help that. I also was told the car has to have a working speedometer that is physically attached to the car which in the Spitfire's case is the in the transmission.
Finally, I personally like the idea of being able to shift once in a while if I want to.

The new flywheel is on used in racing. It is billet aluminum and only weighs about 5 KG.
I am replacing the bell housing, differential housing, rear drums and front suspension hubs with race-proven aluminum equivalents, which should save a few KGs....
The clutch on a Spitfire is smaller than most dinner plates and maybe weighs 2-3 KGs...

The car has been completely taken apart. Every nut and bolt. Dipped, powder coated and primed. Anything that is not needed will not be re-installed which should save a few KGs as well...

The electrical system to be installed was explained a little bit here: viewtopic.php?f=17&t=4422

[johu]

Rigged up a first cut of my hopefully next 12V battery.

Those a 60 Ah NMC cells weighing about 1 kg each. I put some plastic in between them because you shouldn't trust that thin protection foil for electrical isolation.

Currently charging it with a cheesy "2A" buck converter that works also at 7A, at least for now When it overheats it turns off for a moment and resumes after a few seconds. Also found it delivers voltage via a diode in reverse direction, so could hook it up just like that. Of course in reality I will use a beefier buck converter.

Will also run an old 4-channel BMS and simply have it switch off a FET when voltage gets too low or high. So this should only deliver standby load, power the 12V systems for a brief moment and then the DC/DC should take over as quickly as possible.

[X19e]

I do have a similar challenge with the weight as DVD3000 and had nearly the same idea as muehlpower to use a battery from the supplier in his link. But I do like the smaller 24Ah batterie much more. https://www.autobatterienbilliger.de/Ac ... gsbatterie You think that's not enough? It looks like we all got the 12V DC/DC converter with 1000W. Plenty of power for any driving situation, or not? The 12V battery would be never used as long as the converter is powering and that's always when the HV battery is active.
Yes, we still need some power when the HV battery is off:
- BMS: checks the state and waits for control signals from 12V key_in or Charger
- Battery: Water cooling pump/fan
- Hazards and position lights: the requirements for an emergency situation and from the TÜV. The duration is not defined.
What's your estimate? 50W for all above? 70W to be safe (charge the phone, listen to the news)? The datasheet lists an operation time of 240 minutes with this load. Is that enough? Does it fullfill the requirements? OK, you can always got for the larger one.
Let me hear your opinion, please.

But both batteries have the same problem that the available maximum charge current with the DC/DC converter is much higher than specified. Let me provocate a bit, please:
Idea 1: Switch it off during DC/DC converter operation.
My 3.3kW charger (Elcon/TCCharger) has a separate 12V/5A output, plenty enough to charge the 12V battery when the 26.5 kWh HV battery is charged from 20% to 80%, let's say for about 5 hours.
If it's just 12V, it's not sufficient to charge a LFP that needs 14.6V for a full charge!
Idea 2: Separate the 12V Battery from the 12V electrical system
A simple Diode could do the job and same as in Idea 1, the charger will recharge the battery because it will be connected behind the Diode.
Idea 3: Use a separate DC/DC Charger
The Orion-Tr Smart DC-DC Charger Isolated https://www.victronenergy.com/dc-dc-con ... n-tr-smart has plenty of options to deal with 1 or 2 batteries. But it puts another load of 1.8 kg into your car.
Update: Another DC/DC charger, much lighter and cheaper: https://daygreen.com/en-en/products/12v ... s=e&_v=1.0

More ideas? Let's discuss them! For reference: The 12V LiFePo4 battery of an actual Tesla Model 3/Y has 6.9Ah.

Best regards
Frank