[eq1]

^ But isn't IB using the IMA LTO to start? Still, best not to run the auxiliary starter motor through it...

 

[retepsnikrep]

Yes he is, but the first time it tries to crank using the 12V due to a problem.........

 

[jime]

I'm not sure what problem you guys are seeing. The 12V starter test on p 4-7 of the Service Manual specifies 80A maximum. Even that would occur for only a second or so. Cold weather might be a problem, since the cold weather current is unknown but likely higher. Add in the load from the fuel pump and other loads and I guess the device is right on the margin but it doesn't have to function very often???

Looks attractive for my 5 cell pack, since it would cut off at 2.3V/cell unmodified. I'd probably modify it the opposite direction

 

[eq1]

^ I've measured 130 amps, I think JulianEdgar measured around that, and I think IB measured something way higher, though maybe only for a split second... I don't see how it could ever be only 80 amps in stock form - 12V lead acid has massive voltage drop, while the motor itself is rated for 1000W, so it's something like 1000W/~8V=125 amps...

 

[jime]

I don't think the 12V droops that much. The test procedure implies 11.5V for a battery properly charged and in good condition.

I looked at the Toshiba spec for the 20Ahr and it lists the capacity as 1200w/cell. Seems like 5 or 6 cells would be 6000w or more so that seems more than adequate to handle the starting load.

I suppose there might be a issue with his minimum voltage cutoff device. It does seem marginal. Maybe we are mixing two issues??

 

[eq1]

I don't think the 12V droops that much.

hmm, maybe. Plucking that value from my head, I could have sworn it was a real-world measurement from someone around IC... I was actually thinking it was more like 7.x. But I could be wrong.

I looked at the Toshiba spec for the 20Ahr and it lists the capacity as 1200w/cell. Seems like 5 or 6 cells would be 6000w or more so that seems more than adequate to handle the starting load.

Yeah, the 20Ah Toshibas shouldn't have any problem with 12V start. I imagine they'd uphold a solid voltage, like no less than the nominal, so 5 X 2.3V=11.5V or 6 X 2.3V = 13.8V.

In which case the current would be this, right?: ~1000W/11.5V=87A, or 72A at 13.8V...

Though I don't know how Insightbuyer measured 200+ amps - with his LTO 12V battery, in another thread.

I suppose there might be an issue with his minimum voltage cutoff device. It does seem marginal. Maybe we are mixing two issues??

I was just thinking the starter current is around 130 amps and the voltage cut device is rated for only 100 amps.

 

[retepsnikrep]

It's not the batteries or the voltage that's the problem per se, or possibly the starter motor current when actually running, it's likely the instantaneous cranking current when the 12V starter first engages from standstill and is getting the engine upto speed that will be outside the capabilities of that device.

In the device data sheet it specifically warns about it not being suitable for this.

 

[insightbuyer]

I got my device hooked up today and really happy I finally have it installed. After spending the time building the 6 cell LTO replacement battery, the last thing I wanted to do was run it to 0 volts. I was actually a bit paranoid since I installed LTO battery that I left a light on in the car or something that would drain my battery.

Just to clarify a couple of things. The Insight has 2 wires that come off of the 12 volt battery. One is for the 12 volt starter and goes directly to the starter motor, the other is for all other car 12 volt systems. You do not put the cutoff on the starter motor. The starter draws no current when not cranking so it doesn't need to be on the switch.

In the picture below you can see the wire I cut into to install the cutoff, while leaving the other wire intact.

The starter motor does not draw 80 amps when cranking the engine. It draws around 300 amps at 13 volts with my LTO pack.

The 80 amps you are referencing is from the owners manual, but that is with the starter motor clamped in a vice and not installed on the car. You test the starter motor out of the car and it should test 80 amps or less. Reread the starter motor troubleshooting section and it says to clamp the starter in a vice. After googling this, it is normal for a starter motor to draw 60-150 amps with no load.

My LTO pack starts the motor very strongly, and draws 300 amps peak current.

Here is the wire I cut into. This wire leads to the fuse box in the engine compartment. You can see the other wire that goes directly to the starter.
I crimped those connectors, and then soldered them to make sure they never come loose.

Here is the cutoff switch installed. I will have to do something about mounting it better. The ring terminal connectors are exposed and I covered them with tape until I find a better solution.

It needs a connection to ground and I just soldered it to the ground connector.

Here is the maximum amp draw when starting my car at around 13 volts. I checked this multiple times and it is around 290-300. I set my amp meter to record the maximum amps, so it may only draw this for a very short time.

 

[jime]

Ah. After all the large wire is dedicated to the starter, as you say. No current at all on that line when the car is parked.

Thanks for sorting that all out. Now it all makes perfect sense. I think I will copy you yet again.

 

[insightbuyer]

There is a little paragraph about using it for combustion engines in the manual. I didn't know that the starter motor had a separate power line either.

It's definitely worth using this because its somewhat easy to run your battery dead either by the 12 volt not charging or possibly leaving a light on, like the little hatch light on.

From the manual:
Use in combustion engine vehicles The LVC12 typically has sufficient current rating to run all 12V systems in vehicles except the starter motor! In many vehicles it is possible to leave the large starter motor power wire connected to your battery directly, and wire the rest of your vehicle’s 12V system through the LVC12. This way all loads on the 12V system can be isolated (including the ignition signal which triggers the starter motor solenoid) without damaging the LVC12 when the starter motor runs.

 

[retepsnikrep]

Testing one of the new more expensive 4S Lifepo4 balancer board gave good results.

This achieved a balance of the 4 cells in my 20ah A123 test pack to within 5mv,
which is pretty good and more than enough for practical purposes.

I'll install it in the car in due course.

US $13.34 11% OFF|3 4S 6S 7S 8S 10S 13S 14S 16S 20S Active Equalizer Balancer Lifepo4 Lithium Li Ion LTO Battery Energy Transfer BMS balance Board|Battery Accessories| - AliExpress

 

[insightbuyer]

I'm not sure about that particular cell alarm logger, but some of them only draw 8 volts, and will only draw power from 2 of your 4 cells. That will cause an imbalance in those 2 cells that those cell balancers will need to deal with on a continuous basis. Not a big deal, but just saying.

5 mv is very good. I personally balance my LTO cells to within 2mv of each other but 5 mv would be fine.

The big question is if I bought one of those balancers if it would also be 5mv or if you got lucky.

 

[IamIan]

~5mV should be fine .. Myself I'd be ok with anything less than about ~50mV of balancing.

There is really very little Ah or Wh of difference between say 3.600v and 3.650v .. or between .. 2.850V and 2.800v .. I would always recommend leaving at least a little bit of buffer room on both top and bottom .. even say a 5-95 use window should still be leaving enough buffer to allow as much as a ~50mV difference to be fine.

 

[insightbuyer]

Well, partially true. It depends on the cell chemistry if we are speaking about 50 mv.

A123 cells, which I believe retepsnikrep is using is pretty huge because of the very flat discharge curve. Just image balancing a123 cells with 50 mv, it would be pretty bad.

The toshiba LTO cells, its like .02 volts is an amp hour. so 50 mv would be about 2.5 amp hour of capacity.

 

[IamIan]

Myself I'd be ok with anything less than about ~50mV of balancing.

Well, partially true.

Nope .. sorry to break it to you .. but you're wrong .. not partial at all .. it is 100% true that I'd be ok in the context here with anything less than about ~50mV of balancing .. and what I am ok with is 100% up to me to decide

It depends on the cell chemistry if we are speaking about 50 mv.

This context doesn't have multiple different chemistries .. it as one battery Peter put together of A123 AMP20M1HD-A cells .. but even if it did .. it would be more accurate to write something like .. It would depend for you .. because only I get to decide what I'd be ok with .. and if I choose to be ok with less than ~50mV , that is what I've chosen .. I don't get to chose what you would be ok with anymore than you get to decide what I'd be ok with.

A123 cells, which I believe retepsnikrep is using is pretty huge because of the very flat discharge curve. Just image balancing a123 cells with 50 mv, it would be pretty bad.

Yes he is using A123 20Ah pouch cells AMP20M1HD-A.
I disagree with your conclusion .. I don't think it would be pretty bad .. not even bad at all .. if balanced to less than about ~50mV , I'd be ok with it (in a 5-95 use window).

The toshiba LTO cells, its like .02 volts is an amp hour. so 50 mv would be about 2.5 amp hour of capacity.

I'm skeptical of this claim.

Even assuming you are referring to the modules form the Fit people are using.

None of the tests I've done or seen of the Toshiba SCiB LTO cells show the ends (where it matters in this context) of a cell charge or discharge being linear like that .. so using linear logic there is questionable .. the ends top and bottom are far more exponential than linear .. the ends matter in this context , because it is the ends where a cell gets over charged or over discharged.

Under your linear logic of 50mV ~2.5Ah .. that would mean from 1.900v to 2.600v .. which is still in the OEM usable range .. aka a 700mV difference , those Toshiba SCiB LTO Fit cells would give 35Ah in that range .. which no test I've seen of them show that .. because the ends (top and bottom) are far more exponential than linear.

I'm a little confused about what you think this graph is showing ??
Because it looks to me to be supporting what I wrote.

1st .. it's a different battery .. not the one being used in the context of my statement (AMP20M1HD-A ) .. unless you plan to use those A123 26650's to make a 12v car battery (context of this thread).

2nd .. to me .. even if you did want to use that battery .. context of this thread to make a 12v car battery .. instead of the one Peter is using (that my coment was about) .. I'd still say the same thing .. I'd be ok with anything less than about a ~50mV balance (with a use range of 5-95) .. look at the ends of that discharge graph you posted .. the point where a bad out of balance cell could hit the bottom first .. aka how much capacity is left in the last ~50mV on the bottom .. In my subjective opinion the wh/ah left in that ~50mV is a small amount of Ah / Wh .. so small that in the 5-95 window I described , I'd be ok with just being less than ~50mV , even with those 26650 LiFePO4 A123 cells in your discharge graph.

Although I myself .. I also wouldn't use just a 1p4s pack of 2.5Ah 26650 cell A123 cells like that for a 12v car battery replacement .. the ~20Ah AMP20M1HD-A cells Peter used , maybe .. 3P4S of the AMP20M1HD-A , that would be more in mine of my own personal preference .. but .. that's just me .. to each their own.

 

[insightbuyer]

I see this as being an issue, but I'm not 100% here as I have not looked at this in years. This is why I decided against using A123 or LifePo4 cells for my lithium ion insight conversion. I actually was donated on this board an lifepo4 cell to run some tests on them and quickly determined they were impossible to determine the SOC. Then I learned on the internet that they need special care when balancing and reading SOC.

A123 cells have an extremely flat discharge curve. They stay mostly at exactly the same voltage for 90% of their discharge life. This means that if you tried to balance them at this flat discharge curve, it is very difficult and I'm not even sure if its possible to keep a balancer on them all the time. They need to be balanced only at the highest and lowest voltages I believe.

You would probably need a special hobby charger balancer that only balances the cells at a certain voltage.

I personally like to keep my pack at about 50% capacity all the time. What would happen is if you tried to balance them at 50%, then you would have an extremely out of balance pack if you fully charge or discharge your pack. If you were doing this in the insight, the balancer would try and balance the cell at 50% capacity, then when you fully charged your pack you would be over charging many cells as the pack would be so out of balance.

Now to the LTO pack capacity and voltage:

In the picture I attached, you can see that each amp hour is about .02 to .03 volts for most of its complete cycle life for a 20amp hour LTO. Unless you are above 2.6 volts. 50mv is about 2 amp hours for move of the packs discharge curve.

What I'm saying is, if you are going to use A123 or LifePo4, just throw that junk in the garbage and get LTO. If you can't read the state of charge, then its just as much as junk as the NiMH. What makes the LTO so great is you know exactly the SOC, it can also be balanced at any voltage because of this.

http://imgur.com/ytwV2UR

 

[retepsnikrep]

It's horses for courses.

A123 are lighter, more power dense and higher voltage than LTO, so you get more Ah for your Kg and need less of them to build a pack.

The A123 20ah Lifepo4 do have a flat charge/discharge curve so that's why you count current in and out and top balance them.
The techniques are well understood and fairly simple. You can get multi cell BMS for A123 for just a few $.
They also have a useful feature that when full or empty the voltage rises or falls quickly and that's easy to detect.

When I first built my 20ah pack over ten years ago I had my own BMS and balanced them all at the top.
Then I discharged the pack with a known load until the first one reached empty whilst counting current all the way.
That gave me the pack capacity 100-0% capacity lets say ~19Ah.

As they are very efficient (they don't waste much energy) you simply count current in and out to work out the SOC.
Every so often you do a sort of recalibration and top or bottom balance etc to reset any SOC counting drift.

LTO are rugged and seem good cells.
They do have the useful voltage balancing capability.
i.e. Charge them all to X volts for X% SOC.

Each has their place and application. I won't throw my A123 into the garbage just yet

 

[IamIan]

What I'm saying is, if you are going to use A123 or LifePo4, just throw that junk in the garbage and get LTO.

I prefer ... Reduce .. Reuse .. Recycle ..


I'm not a big fan of throwing into the garbage those items that can still reasonably be reused or recycled .. sure if Peter found his old cells were defective , it would be time to recycle those defective cells .. but if someone has some A123 LiFePO4 cells that are still reasonably functional .. I say reuse them.

In the picture I attached, you can see that each amp hour is about .02 to .03 volts for most of its complete cycle life for a 20amp hour LTO. Unless you are above 2.6 volts. 50mv is about 2 amp hours for move of the packs discharge curve.

FYI .. In the picture you attached ..

18Ah to 19Ah is a 70mV difference for 1Ah.
19Ah to 19.5Ah is a 350mV difference for 500mAh

You would see something similar on the top with a charge curve as you see here at the bottom on this discharge curve.

 

[insightbuyer]

Having a battery low voltage cutoff switch was way worth it. It is very nice to know that you will never have a dead battery.

I added a momentary switch to my voltage cutoff switch. If the battery goes below 12.65 volts, I need to press this switch to turn it back on and I have 10 seconds to start the car if the battery voltage is below 12.65 volts. You could also short the two contacts together or to ground with a wire, but its just nice to have a switch to do it.

I also tested the cutoff switch in the car. I turned the lights and radio on when the battery was at 14.2 volts. It took 40 minutes with the lights and radio on to hit 12.65 volts and the car went dead instantly.

I then pressed the momentary switch and it came back on and stayed on as my battery voltage was at 13 volts since I turned off the car lights.

 

[insightbuyer]

Just to show you easy it is to kill your 12 volt battery. Just luck that I went in my yard yesterday to check up on something and I noticed I left one of my dome lights on. I left the light on because I was looking for something I left on the passenger floor earlier and forgot I turned it on. It was left on for only 4 hours.

This light draws .4 amps, so my battery would have been dead in about 30 hours at this rate, and I would have exceeded that time by many hours. The dome light is so dim that its hard to realize you have left it on.

If you are running a lithium ion battery you really want a low voltage cutoff switch.