Electrical Lifepo4 Battery Replacement

[jrichker]

The concern that I have is the overvoltage condition. Aside from assuring the voltage regulator on the alternator has a limit of 14.2-14.6 volts, there is very little you can do.

External devices are limited to a shut regulator which would have to be capable of withstanding heat and moisture and be of sufficient power capacity to do the job. Simple 1 or 2 component shunt regulators do not have the power handling capacity needed. More complex shunt type regulators with multiple parts are possible. However, they would need to be designed by someone with a good understanding of electronic design and the automotive environment the regulator would operate in.

If you have a minimum of a 2 year degree in electronics and 4 or more years experience as an engineering aide or electronics repair tech, you might attempt it. From what I have seen so far, I don't think that accurately describes you.

 

[blackstangt]

I'll post my solution.

 

[blackstangt]

Solution:

To back up the voltage regulator on a standard alternator, an in-line regulator at 14 volts can be used. These are a little expensive ($150) and will cause a drop out of about a volt. If the car charges at 20v, it will drop to 14v, if the car charges at 15v, it will meet the desired 14v charge. However, this would also mean a car charging at the ideal 14.4 volts drops to 13.4 volts. That's perfect for a LiFePO4 battery, because that is where they last the longest. It isn't ideal for a lead acid, which should be charged at 13.8-14.2 v (14.4v Max). 13.4v is still going to charge the battery and keep systems in the car functioning properly, but won't recharge a drained lead acid battery up to 12.8v very quickly.

If a car manufacturer or enthusiast wants to have a perfect system, they should use a LiFePo4 battery with a good voltage regulator at 14.6 volts, with an in-line regulator at 14v output, to ensure a voltage no higher than 14v and a much more stable charge. For a lead acid battery, an alternator with a 14.8v regulator backed up by a 14.4v in line regulator would be ideal. Standard charge would be at 13.8v and never more than 14.4v.

I'll keep looking for a cheaper solution, but that seems like the best option, expensive as it may be.

It looks like manufacturers are stating a safe overcharge of up to 4.2 Volts per cell without damage to the battery, so the LiFePO4 can handle 16.8 volts. A lead acid would boil over or explode by then.
http://www.powerstream.com/LLLF.htm

I'm going to run the LiFePO4 battery with only a fuse since that's higher than a lead acid battery could handle.

I'll post updates on the battery's performance throughout the winter and in the spring when I put my Mustang back on the road.

 

[jrichker]

@blackstangt

Where is the information on the voltage regulator? You didn't include a link for it in your post.

I will be interested in seeing how this works. You bought a battery that is more expensive than the regular battery and then spent an additional $150 to get an unknown voltage regulator. That's a lot of money to invest in something that doesn't have any track record here in the Fox Mustang world.

 

[blackstangt]

"I'm going to run the LiFePO4 battery with only a fuse since that's higher than a lead acid battery could handle."

 

[blackstangt]

They have the best track record of any battery chemistry in motorcycles, electric cars, electric motorcycles, solar power, wind power, RC cars, etc. Mustangs are not different from other cars when it comes to electrical needs, and only slightly different from modern motorcycles. I have been aware of its potential for about a decade, but the cost has always been too high to get adequate cranking amps until more recently.

People spend a lot of money on a fiberglass hood or aluminum heads to save weight, 100 dollars more than a lead battery seems minimal by comparison.

 

[blackstangt]

I don't have the link from the specific one, but google something like this.
http://www.chargingchargers.com/converters/sdc60.html

 

[jrichker]

@blackstangt
That will not succeed in doing what you need it to do. It takes a much higher voltage and reduces it to a lower voltage using switch mode technology. The difference between what the alternator puts out at max voltage of 14.8 and the 14 volts you need is only .8 of a volt. That will be difficult to find in a regulator that can handle 65-75 amps or more. You may find such a device, but it won't be cheap and may not be suitable for the harsh automotive environment of 170°+ underhood temperatures plus high moisture when it rains.

I am an old guy, 68 with 50 years experience fixing cars, some of that time as a professional mechanic when I was much younger. Just in case you have any doubts about my ability to evaluate electronic problems and answers, I have a 2 year degree in electronics and 35 years experience fixing computers and electronic equipment. I don't miss very often when it comes to electronic problems in computer or automotive applications.

I do know that while you can bolt on cylinder heads, intake manifolds and such, and get away with it. Simple bolt on mechanical stuff doesn't take a lot of high level skill. However that approach doesn't work with electronics. It take a lot more smarts about how things work to come up with reliable and efficient solutions to electronic problems.

Automotive electrical parts like alternators and batteries are designed to work as an integrated system. The voltages and charging rates are designed to work together from the beginning. What is needed is an alternator designed to work with a Lithium LiFePO4 battery. The closest thing to that is a adjustable replacement for the stock alternator regulator from http://store.alternatorparts.com/v1300-regulator-12-volt-b-circuit-14-2-vset.aspx or http://www.aeroelectric.com/Mfgr_Data/Regulators/Transpo/V1200_Transpo.pdf

 

[stykthyn]

I'm with jrichker, while the idea was intriguing it seems that the battery just isnt designed to mesh correctly with the rest of the mustangs electrical components. perhaps relocating the battery to the trunk, while not exactly saving weight, would in fact transfer the weight to a more desireable location.

 

[blackstangt]

The stock regulator should put out 13.8 to 14.2 volts and a maximum of 14.4 volts. This, as well as the 14.8 volts my worn out regulator peaked at should work just fine. In fact, my lead acid battery was probably at more risk of over-voltage than the new lithium one.

It will only lose 1 volt, which is 13.8, which is acceptable.
There are plenty of dc to dc converters that handle more than that.
You don't need to put it under the hood.
This is an idea for enthusiasts and potentially car manufacturers, as there are other benefits to stabilized voltage. Not for me.

Thinking a LiFePO4 Battery is less safe than lead acid is a miss. Though that's chemistry, so it isn't a lack of electronics education or experience.

The Mustang electronics system was never designed properly, a 65 Watt alternator? There's a reason people upgrade to 95W or 3G alternators. This is the same thing, an obvious upgrade to those who know batteries. I built an electric vehicle, among other things, I know batteries. I'm more surprised we see lead acid in cars still, I wonder how high gas prices have to go before they swap them.

 

[jrichker]

Since you feel that you have all the answers, I will bow out and let you deal with the problem yourself.

 

[blackstangt]

Typical internet communications. Debating irrelevant points and not comprehending the message. The battery works. I just want to make the system better and share it.

 

[blackstangt]

@stykthyn What in our conversation has led you to believe that the battery is not better suited for the task than a lead one? If you want to move your CG, you can add weight lower than 2-3 feet off the ground and farther back than the trunk/hatch area, meaning less weight to accomplish the same task. You also won't have the possibility of venting fumes in the car.

 

[stykthyn]

Seems that there is not yet a cost effective way to correctly regulate voltage from the alternator long term.

 

[blackstangt]

A lead acid battery would explode at the voltage it takes to damage a LiFePO4 battery.