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LTO/BCAP Lead Acid Replacement

Mr. Pink

New Member
Joined
Jan 26, 2020
Messages
5
Location
Germany
Hi together,

after watching Will’s second video on LTO batteries I thought I share my LTO/BCAP replacement built for my car.

Since my car used to eat up lead batteries roughly every two years, my initial idea was to build a replacement with BCAPs only as I was not convinced by LiFePO4 car batteries due to their limited high current capabilities. Since the LTO cells became reasonable priced lately I added the LTO cells to the setup.

The setup consists of the following components:
  • 6x Yinlong LTO66160H 40Ah
  • 6x Maxwell BCAP3000
  • 6s 5A LTO active balancer

The capacitors and the batteries are connected in a serial/parallel configuration to allow for a single balancer setup and having the capacitor leackage current directly compensated by the battery cells.

1386A0A2-205E-44B9-A6CA-65B24B8240E1.jpeg
The active balancer keeps the voltage difference within 10mV and is rated at a maximum balancing current of 5A. Additionally I connected an IDST BG-8S to monitor the cell voltages though it has no direct LTO support currently.

The capacitors are interconnected with 25x5mm copper bars while the rest of the cells are connected with 35mm2 equivalent copper bars.

So far I measured a maximum current of 410A at the battery while cranking the cold engine with the voltage dropping to 12.5V at the battery terminals (initially charged to 13.6V).

After now 3 weeks of driving with the battery I am very happy with the replacement.

The major draw backs I see with using LTOs (in combination with BCAPs) are:
  • using 6 cells in series for a voltage of 13.8V keeps the cells well below the maximum possible capacity/charge - I assume that in this setup, the battery has only 20Ah when fully charged rather than 40Ah possible
  • high current load on the alternator when discharged potentially damaging the alternator at low RPM - since the alternator is water cooled in this car I am currently neglecting this aspect
  • more expensive than LiFePO4
On the other hand the advantages are:
  • 20,000+ cycles for LTO cells and 1,000,000 cycles for the capacitors
  • high current capability
  • save chemistry
If I had to build it again, I would probably split the battery into separate modules, i.e. LTO and capacitors, potentially using only the LTOs as the first step.

Philipp
 
This is awesome. Really exciting post.
If you had more cells like 3p 5s, do you think the capacitors would be necessary ?

Wondering how would the alternator behave on that without having to convert the 14.6 to 14V.
 
This is awesome. Really exciting post.
If you had more cells like 3p 5s, do you think the capacitors would be necessary ?
I would rather say, that even with only one string of cells the capacitors are not necessary at all, at least not for the car I have.
Neither the alternator nor the starter do exceed the maximum charge/discharge rate of 10C.
Doubling the capacity by adding another string sounds reasonable though.
Wondering how would the alternator behave on that without having to convert the 14.6 to 14V.
What exactly do you mean?
 
I would rather say, that even with only one string of cells the capacitors are not necessary at all, at least not for the car I have.
Neither the alternator nor the starter do exceed the maximum charge/discharge rate of 10C.
Doubling the capacity by adding another string sounds reasonable though.

What exactly do you mean?
I was wondering on the 100% State of charge voltage vs the voltage provided by the alternator.
Somehow I thought that you're using 5 cells in series +capacitors and 100% SOC was 2.8 (14V)

However by reading more on the chemistry looks like native voltage is 2.4 with peak at 2.6V so 2.4 x 6 you have 14.4 or up to 15.6 volts.

Your alternator should give more than 13.8 , do you think the alternator regulator could be tweaked to give 14.2 ?
 
Your alternator should give more than 13.8 , do you think the alternator regulator could be tweaked to give 14.2 ?
Unfortunately, the alternator being water cooled is a sealed unit. Thus, the regulator itself is not accessible. Maybe I can tweak it by changing the voltage on the control terminal though - have not tried that, yet.
 
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