light weight battery kills the alternator?

[Yetti]

I realize this is an electronics question although it seems much more people who run autocross / track days would run into this.


With my want to make the car faster and run better times in AutoX I installed a light weight lithium iron battery last week, this is the exact one:


https://www.summitracing.com/parts/dtn-btl24a480cw



Then fast forward to this weekend on Friday went to a test and tune and the car ran great. Then when leaving the site every so often a bunch of the lights on the dash would come on, the speedometer would go to zero and the car would jerk for a split second then go back to normal and this happened once every 10 - 15 seconds. It did this a bunch of times in a row and then would be good for a while and come back from time to time.


Drove to the auto parts store and the battery tested good but the alternator showed bad for a diode. So I bought another alternator and installed it. Ran the event Saturday and Sunday with no problems and then when leaving the site after everything was over it did the same thing a couple more times on the way to the gas station (with the new alternator). After filling up with gas it was all good for the 200 mile drive home. It just seems weird that the alternator would be failing again when the new one has been in the car for ~ 2 days and a couple hundred miles.



My car is a 2013 FRS, manual trans to be specific.


1. Has anyone had a similar experience after installed a lightweight battery into their car?



2. I have run almost exactly the same battery in a couple other AutoX cars with zero problems, does the FRS need some capacity or grounding change on the charging side when running a much smaller battery?

[Ultramaroon]

There might be something weird with the battery.

There might be an intermittent connection somewhere, and there was nothing wrong with the alternator.

There might be the same thing wrong with your new alternator as what was failing in the old one.

There are many possibilities. Time to bust out the multimeter and start testing. Maybe start with reinstalling the original battery and run with it for a while. If the problem reappears, while it doesn't mean there's nothing wrong with the aftermarket battery, you're safe to continue troubleshooting with a known-good battery.

[Eric1855]

Probably the battery, not the alternator. My car acted all kinds of weird, random lights on dash, weird stutter, right before the anti-gravity battery swelled way up and smoked and may have exploded if not caught early. Other ones before I had the car just die, run fine, shut off, go to turn on and nothing. All dead.

I know they work fine for some but Ive had nothing but trouble with lithium batteries, of several brands, and just went with a Deka AGM, its still significantly lighter than stock and is rock solid even if the car sits for a week or two or if I leave the racecapture on, no issue.

[geraldjust]

Controversial take but I wouldn't recommend lithium ion batteries for these cars. These cars were actually meant for AGM type. So the charging curve for the current sensor/temperature sensor. They have a very specific type on how it charges the battery. thats why these cars need the current sensor on the neg side of the battery.

The way the electrical charging system works is for any given current the car wants to then bring up the charge voltage on the alternator up. To counteract it and when averaging out current going in and out of the battery constantly, its basically net slightly positive tp be able to charge it.

Lithium ion battery on the other hand will charge with as much current you can throw at them. (as long as you dont exceed its max charging current). If you do, thats what the BMS is for. But how BMS works normally is by shutting off the "in" on the post on the battery. this will keep the battery safe but can cause huge voltage spikes from the alternator. So every 10-15 second sounds like the BMS interfering somehow.

Unfortunately, if those huge spiked did occur, they is always a chance you can damage internal charing components in the alternator. Or the BMS inside the lithium battery. Or both.

Honestly maybe try and get a smaller quality AMG type of battery.

[Breadman]

is your battery getting low voltage? When i was running a lithium battery i had to leave the headlights on or id get low voltage. It was weird

[ZDan]

Originally Posted by Breadman

is your battery getting low voltage? When i was running a lithium battery i had to leave the headlights on or id get low voltage. It was weird

Normal on '17+ for voltage to drop at times. It's strategically minimizing alternator drag during cruise and accel and then giving full 14.2v during decel. Mine did the same from day 1 with the factory lead-acid battery as it does now with Shorai Li battery.

[Yetti]

I did put a volt meter on the battery while running and it was around 14.1 - 14.2 volts with the first alternator. I will check on the 2nd one. I remember checking the battery voltage car off at the same time and it wasn't low, don't remember exactly the number.

[Ultramaroon]

Originally Posted by geraldjust

Lithium ion battery on the other hand will charge with as much current you can throw at them. (as long as you dont exceed its max charging current). If you do, thats what the BMS is for. But how BMS works normally is by shutting off the "in" on the post on the battery. this will keep the battery safe but can cause huge voltage spikes from the alternator. So every 10-15 second sounds like the BMS interfering somehow.

My very first thought. Only controversial when not understood.

[Matt93SE]

Been running a Shorai LFX battery for years in my race car. only time I had a problem was when I installed a Yuasa 'battery tender' on it and walked away for 2 months during off season. when I came back, the battery wouldn't hold a charge. I took a look and it was swollen with the cap cracked.

My guess is the tender tried to do a desulfate operation sometime during storage and caused the battery to assplode.

Since then, I replaced with another same Shorai (because custom battery bracket and lack of time to do anything else..), but I also bought the $$$ Shorai charger/storage guy and keep it on that when I'm not driving the car.

For a DD, you wouldn't need the charger/storage guy.

[CSG Mike]

I've not seen a battery kill the alternator.

[jflogerzi]

Glad I ordered the Tomioka Racing 6 lbs AMG Light weight battery. Also will keep it on a charging Tender as its no longer my DD.

[Matt93SE]

Originally Posted by jflogerzi

Glad I ordered the Tomioka Racing 6 lbs AMG Light weight battery. Also will keep it on a charging Tender as its no longer my DD.

Just be sure whatever tender you use on it is compatible with the battery type. LiIon batteries can be charged by a standard charger, but you don't want to leave them on a standard tender long term. IIRC, AGM batteries don't like to be de-sulfated either, to be sure to look into the charger's compatibility with that battery type.. do it thru both battery mfr and charger mfr information, cause the charger people will say "it's compatible with everything".

[Ultramaroon]

Originally Posted by CSG Mike

I've not seen a battery kill the alternator.

My Eclipse snacked on alternators every time I accidentally drained the battery. I eventually replaced the internal regulator with a beefy external one from an F-150. Problem solved.

[Yetti]

Ok just checked with the current alternator and the battery is 13.3 volts with the car off (which seems kinda high). The car is not daily driven so it has been sitting since it got home from the AutoX yesterday and with the car running it is at 14.3 volts.