DC's DC DC-to-DC build thread

"What are the SoC voltages for LTO, btw?"

Batteries are SCiB from batteryhookup, rated 20Ah/46Wh per cell, with 2.8V charge, 2.3V nominal, and 1.8V cutoff.
I tested few configurations and choose 7S1P with limited charge at 2.58V max per cell, to use stock Viofo HK4 cable.
Even with limited charge voltage, these batteries provide 100% capacity at low, 1A constant draw (about 12.5W draw at lowest - V cutoff)
So the SoC for the pack is: 18.06V max by charger and 12.6V cut off by HK4 (at above 18.1V, HK4 treats the battery as a 24V system).
(all tests so far are done without BMS, which just arrived from AliExpress)
 
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You’re using a separate regulator to knock that back down to sub-15 V right? Now I get why you were testing only step up converters, but car electronics aren’t always tolerant of much over 15 V.

More specifically, why not do 6S1P for 12 V or jump over to 10S1P for 24 V?
 
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Pipe dream of mine is using a SBC to intercept the rear-camera USB cable to autonomously connect to the dashcam after the car has been turned off in order to download the footage from the previous drive and back it up. If this can be executed, then a directional antenna is all that’s needed to connect to a home NAS and drop it there afterwards.

Opto-isolators and linux with a CLI script should easily be able to execute this. Don’t need too powerful of an SBC. Need to see what speed the N4P connects at.

Additionally, I do have some technical/mechanical hurdles for rear camera placement so for the time being, I’m running only the front camera.
 
DigitalCorpus said:
You’re using a separate regulator to knock that back down to sub-15 V right? Now I get why you were testing only step up converters, but car electronics aren’t always tolerant of much over 15 V.

More specifically, why not do 6S1P for 12 V or jump over to 10S1P for 24 V?
Click to expand...
Why should I use separate regulator?
The universal boost converter/charger, with adjustable output works like Renogy, except, I can adjust output V and A in a very wide range for charging.
Charger takes in 12-14.5V from car battery/alternator or cigar socket and converts it to constant 18V and constant 6.4A, as I set it for 7S1P pack. (6.4A is my limit for cigar socket, 6.4A x 18V = 115.2W. If I go to alternator/car battery, I can set it up to 20A.
These boost converter/chargers can be adjusted and used from 6S all the way up to 24S.

6S1P cut of voltage is 10.8V which is below HK4 lowest setting at 11.8V.
7S1P pack with upper limit at 18V and lower cut off limit at 12.6V, provides 320Wh capacity and works well with Viofo stock HK4 hardwire kit - No need for additional output converters. It is quite compact and I don't need more capacity.

Since these chargers don't have soft start, I will use ACC activated 10 sec time delay relay (TDR) between alternator/car battery and charger, to ensure alternator car battery is not overloaded additionally stressed by charger during engine start.
When I am ready (hopefully soon), I will start new thread on LTO with all the details.

Edited in bold.
Gary P
 
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GPak said:
Why should I use separate regulator?
Click to expand...
Because the buck converter in the in line device may not support 24 V input range and 18 V is beyond the normal range for a 12 V buck regulator. Then again, I didn't note that the HK4 supported 24 V systems so the point is moot.

GPak said:
Charger takes in 12-14.5V from car battery/alternator...
6S1P cut of voltage is 10.8V which is below HK4 lowest setting at 11.8V.
...Since these chargers don't have soft start, I will use ACC activated 10 sec time delay relay (TDR) between alternator/car battery and charger
Click to expand...
These details here is where my concern lies. If you have a battery/alternator SoC ~14 V and your LTO pack is below that, you can run into some problems which can let out the magic smoke. Not all controllers/converters (a notable distinction but trivial in this particular case) handle this well. Some will have finite limits to upper limit of the duty cycle of the switch (MOSFET) and some won't.

When Input Voltage > Output Voltage you need a step down converter and step up converters can have a failure mode of short circuit. I would highly advise setting your cutoff 200 mV to 500 mV higher than the maximum voltage of your supply

Soft start is a feature designed to limit inrush current during the first second of operation. The TDR is fine, but is a distinctly different category. The lead acid starter battery will act as a limiter for you if the alternator is not running. If you see light dim by a the duration of a blink of an eye, 200-250 ms, that's when your converter turned on. This isn't something I'd expect you to need to worry about unless the inrush current is high enough to brown out your ECU, but that just means your starter battery needs replacing.

GPak said:
When I am ready (hopefully soon), I will start new thread on LTO with all the details.
Click to expand...
I look forward to your write up!
 
Been very occupied with family and personal health related issues so I did drop off the planet for a spell. I will likely resume activity in a week or two.
 
Good to see you're back!
I hope all your issues are behind you.
 
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