The Completely Dubious Lithuim Ion Cash Box Car Battery

[iamdarkyoshi]

So my dad owns a generation 1 Honda Insight. It is a hybrid car, and the 12v battery (the lead acid battery under the hood) is not charged by an alternator, but rather through a voltage converter from the HV hybrid pack. The hybrid battery pack is charged either in the background from the engine running or during braking. Anyway, my dad has been fed up with replacing the lead acid battery in the car every 6 months, especially considering that the 12v battery is not (normally) used to start the car, the hybrid pack starts it through the integrated electric motor, unless the car deems it unsafe to start with, such as being too far drained.

 

My dad does mail runs, and he often has to leave his lights on, which after a while, it would only take a couple minutes before the lights could kill the lead acid battery.

 

The reason the 12v battery keeps dying is because the car never fully charges it due to a very poor design in the charging circuitry, so a mod can be done in the back of the car that locks the charge voltage at a higher voltage, which can keep the battery happy. But lead acids are spendy...

 

So considering that this battery is only really used for lights, radio, computer, etc. we decided to do something silly: Replace the 12v battery with a large quadrotor battery, which was actually CHEAPER than a NeverStart battery from walmart.

 

The battery we chose has 4 cells, a 10C discharge rating and a capacity of 16Ah. So theoretically it could supply 160A, which is probably more than enough to start the car in an emergency, something the lead acid batteries rarely could do after only a couple months. This being a 4 cell battery, it has a much higher nominal voltage than a lead acid, but with the mod to the charge circuitry, it stays right in the middle of the lithium's charge range.

 

Anyway, if/when the battery decides to forcefully detonate, we decided it would be best that it be in a metal box. So thats what we did.

If you noticed that there is no charge protection here, that is because there is none. Why? We lost the board responsible for handling that. However, after a month or so of use, the cells are within 0.01v of each other, despite never being balanced. Amazing!

 

The posts on the outside are connected to the battery through two wires each to carry more current. The cash box had a nice plastic tray, which I re-used to make the battery holder. The lid has about an inch of foam between it and the battery when closed, and there is 3/4in of foam under the tray as well, so the battery is well protected. The positive post is insulated with thick sheets of plastic and a large hole was drilled in the metal underneath to insulate it from the post's bolt. 

 

 

Anyway, I plan to add the resistive balancing BMS in the middle tray, and it should ensure the battery stays happy.

 

What do you guys think? This battery, BMS (which is lost) and the cash box with posts, wires, etc. is STILL cheaper than a regular battery. Sure, its not rated to start the car, but in this car, it very rarely needs to. So far, it can run the lights and stuff for longer than his 6 month old lead acid battery, so I call it a success!

[iamdarkyoshi]

I typed all of this on my phone. Please kill me.

[Hackentosher]

Well, I never thought I'd see a cheap Turnigy lipo starting a car... You mentioned that the battery is almost never used to start the car, does that mean it's just sitting there idle until the car needs the LiPO? If so, I know that's not good for the battery as LiPOs aren't really supposed to be charged and not doing anything for more than like 10 days. LiPOs are like needy chihuahuas.

[iamdarkyoshi]

4 minutes ago, Hackentosher said:

Well, I never thought I'd see a cheap Turnigy lipo starting a car... You mentioned that the battery is almost never used to start the car, does that mean it's just sitting there idle until the car needs the LiPO? If so, I know that's not good for the battery as LiPOs aren't really supposed to be charged and not doing anything for more than like 10 days. LiPOs are like needy chihuahuas.

Although it never starts the car (unless the hybrid pack is dead) it still needs to run the lights daily, as well as all the other crap we have added (hyrid override system, more audio amps, 120v inverter, etc)

 

The car also seems to hold it around 3.7-3.8v per cell, which is not too bad for storing them anyway

 

It gets the attention it needs. And ya, never thought I would see one of these in a car either. Speaking of turnigy, where is MY DAMN TURNIGY REAKTOR????? Ever since we moved, I cant find it. 20A charge/discharge was amazing.

[ZetZet]

Li-ion batteries are falling in price fast enough that they could indeed replace car batteries soon.

 

Motorcycles should all be using Li-ion already imo.

[Hackentosher]

7 minutes ago, iamdarkyoshi said:

Although it never starts the car (unless the hybrid pack is dead) it still needs to run the lights daily, as well as all the other crap we have added (hyrid override system, more audio amps, 120v inverter, etc)

 

The car also seems to hold it around 3.7-3.8v per cell, which is not too bad for storing them anyway

 

It gets the attention it needs. And ya, never thought I would see one of these in a car either. Speaking of turnigy, where is MY DAMN TURNIGY REAKTOR????? Ever since we moved, I cant find it. 20A charge/discharge was amazing.

My cheap ass imax 6s charger is  good enough. Get's the job done.

[iamdarkyoshi]

4 minutes ago, Hackentosher said:

My cheap ass imax 6s charger is  good enough. Get's the job done.

20A charge/discharge is great for waking up older non-lithium batteries

 

Mine has a USB port for data logging too

[Andrew Storlie]

I have a 4s4p lipo battery that i made myself with full protection circuit that i use for my motorcycle instead of a normal battery. Cost me ALOT more that a normal battery but i have a show bike with lots of lights and of crap that i leave on when im not riding. 3 years so far and still no issues at all. Never had to charge it or float it in the winter.

[iamdarkyoshi]

So my dad has actually had to start the car off of this battery before I put it in the box, and this was when the battery was connected to the wires on the floor in the passenger side of the car (where the inverter used to be). At the time, these wires ran to the nonexistant lead acid battery through a 40A fuse.

 

This lithium battery started the car through this length of wire AND the fuse, and it cranked over faster than a brand new lead acid. So this battery has no issues starting the car, and now the wires are FAR shorter and thicker, too. Should have absolutely no issues now, even though there werent issues before. Pretty impressive.