Replacing Lead Acid Battery with a Lithium - LiFePo4

[toddbailey]

I'm in need of a replacement battery, iirc it's a group 78 for the 1983 944.

So I'd like to install a LiFePo4 battery. I'll need about 700 -1000 cca. According to a cross reference chart that is about 120 amp /hr. To over engineer the replacement I'll put in a 150 amp/hr

With the capacity issue taken care of I have a few concerns

The biggest concern is just how how compatible 944 electronics are with lithium batteries.
Such as the car's charging system. I've heard that in some cases the alternator and other components don't like to be run with out a lead acid battery type loads which leads to over heating and possible fire.

For those who have actually done the upgrade, what road blocks did you run into?
Did you have to install additional components to create a happy marriage between the battery and charging system?

any thoughts or info greatly appreciated

thanks

[Cajundaddy]

We have used LFP batteries in motorsport for 15 years (Boxster/Cayman). The greatest advantage is weight... 5 lbs instead of 50 lbs. They do require some special care and feeding. You really need a charger with an LFP charge profile to top it off periodically and balance the cells. Also they cannot be charged below 32F. We killed a few because we did not understand this at first. The early ones did not have an advanced BMS with low temp charge protection so running them in freezing temps at WSIR in January killed them dead. If I regularly drove in sub freezing temps I would choose small AGM instead of LFP.

Ours are typically powersport batteries and have plenty of cranking amps of 550-700 but a low reserve of only 20-30Ah. As a result we keep them on a smart charger/maintainer when garaged. I would also run a voltage test to make sure your alternator is not charging at 14.6vdc or higher as this will also kill an LFP battery. We found the ideal charge voltage to be 14.0-14.4vdc.

Choosing LFP for your car really depends on your goals and objectives. For highest energy density and low weight, LFP is great. If you just want highly reliable in all conditions and don't care as much about weight, AGM is probably a better choice.

[Monkey Wrench]

I can't speak for the lithium ones except they work great in things like power tools and I was not aware of the problems of freezing temps.

the last lead acid I got was a deep cycle battery and I though that best for me as I tend to park them intermittently and for longer periods than a daily driver.

lithium ones probably wont leak, and they are smaller and the weight difference is nice..

I soak a pad in baking soda and water, let dry and put that under any lead acid battery to kill the acid if it does leak any. - to save the battery box from rusting.

im wondering if some are able to use solar chargers just to keep batteries topped up because that seemed practical,, If I run a charger I have to run an extension cord out, ill do it occasionally but with 5 cars its kind of an ongoing job just to keep them all from dying due to sitting uncharged and unused. I seem to have better luck if I pull one post off when they sit..

once or twice it happened that I neglected to unhook my charger and it cooked the battery, I know they should stop charging. it starts making a stink and the battery can get hot , might be dangerous..

what I do is put on an outdoor light while its charging as a reminer not to leavie it for over 4 hours or so..

I have a big shop charger and some smaller ones, Id like to know how to check the cutout circuit maybe they get stuck and keep charging..

from what I'M hearing charging lithium batteries is one of, if not THE leading cause of house fires. A lot seems due to cheap quality or mismatched chargers. I am not hearing stories of people charging name brand power tools and of those starting fires.

sorry if I'm a little OT but the ones with actual experiences with the conversion can still provide info. - interesting topic for us all.

[djnolan]

CajunDaddy said: run a voltage test to make sure your alternator is not charging at 14.6vdc or higher as this will also kill an LFP battery. We found the ideal charge voltage to be 14.0-14.4vdc.

Question, is alternator charging voltage adjustable?

[Cajundaddy]

Originally Posted by djnolan

CajunDaddy said: run a voltage test to make sure your alternator is not charging at 14.6vdc or higher as this will also kill an LFP battery. We found the ideal charge voltage to be 14.0-14.4vdc.

Question, is alternator charging voltage adjustable?

Depends on the alternator. A modern "smart alternator" can be set up with a specific charging profile to match your battery chemistry and current needs but for this thread we are talking about 944s which are 1980s tech. I have never put a meter on one but would if I planned to run an LFP battery.

The other way to manage this is with a DC>DC charge controller between alternator and battery to set up a precise charging profile to keep your batteries healthy. I use one with a MB Sprinter-based RV with AGM chassis battery and LFP "house" battery which runs all of the living area and inverter.

[Monkey Wrench]

heres' pelican's directions to change the thing, normally I do this in my volvo and its only two screws, then it pops out. but the instructions ask you to remove the whole alternator maybe its an access issue.

this is for a turbo model maybe older ones are different?

https://www.pelicanparts.com/techarticles/Porsche_944_Turbo/55-ELEC-Voltage_Regulator_Replacement/55-ELEC-Voltage_Regulator_Replacement.htm


No it is not adjustable, you can replace it easily though. You can view the slip rings (copper bands) with it removed. if they are rough I've turned them smooth, otherwise the slip rings can be replaced. Id see an alternator shop if that is a bit much.

when you remove them look how long the brushes are, if one is worn more it is an indication of slip ring wear or roughness. you can just peer inside and have a look at them. the most common failure is the brushes get too short and loose contact. replacing the unit will normally restore operation if the slip rings are rough then the brushes will wear out faster. - but it may get you home.

while the belt is off jive it a spin and feel the bearings, if they are rough or noisy at all,
replace the bearings.

no the voltage isn't; adjustable , i believe it was with generators and maybe with early alternators it was a separate unit on some cars early on.

often the problem is just that the brushes are worn out, you can replace only the brush Ill usually solder the wires about midway . If I do that. its a few minutes faster just to replace it as a unit. If you are broke, do that. the bri=ushes are really easy to file if you ever need to use others because you are stuck , filing a carbon brush is like filing a pencil, very easy. so you can adapt others , if necessary to get home.

you can compare to the one used in a Volvo 240 or 740 I believe its the exact same part. Porsch bought them from Bosche anyway, or so I believe. other than the bracketry it is very easy to switch alternators between vehicles , i put a very common GM one on my old volvo , easy to get or replace .. they all charge the same voltage of battery and other than the idiot light which is just one wire that's about it for wiring differences.
It is good to actually take the time check the ground from alternator to battery negative it may use the engine as a ground point. check that , it can cause issues if dirty. if the alternator looses its ground. it will appear as a bad alternator. I bought one once to find it was only that.

maybe some have a smaller pulley , the pulley ratio influences its speed but it is somewhat unimportant
here is a schematic for a voltage regulator , it is possible to mount one separately but I think this is getting to be a bit much for the average shade tree mechanic.



https://www.electroschematics.com/current-limited-alternator-battery-charger-control/

in essence the windings are regulated when they are switched out because it is at full voltage then it stops charging. one might look into available voltage regulators it is possible that an adjustable one could be available.
here is a schematic , likely a bit daunting but with that you could likely build one if so inclined.

generators work under some different principles and they usually had a regulator that could be adjusted with a screwdriver. I doubt the 944s ever had a generator, the alternator is generally a more modern -er,,,, alternative ;-)

a lot of older bikes may be adapted because wet cells can leak whereas the solid state sealed batteries are unlikely to leak acid. also Harleys are so poorly balanced
by inherent design, they shake everything.. and are likely to have extravagant paint jobs to protect.

I generally replace them with the largest I can fit and stick with a wet cell but these do have some advantages. one thing I like to do is extend the connecting wires so that my battery can be turned either way. I like keeping that adaptable and its' only a bit more wire.

the top posts in a 944 are a bit close to the hood so if you clip a charger on and close the hood it may short to the hood and make a burn mark. maybe a bit of plastic stuck to the hood could work as an insulator to prevent that. Just pay attention to the clearance if you have to close the hood with your charger connected.

I don't know if its the same in all areas but if I have a bad alternator or a starter I go to a local shop that does that and that's their specialty. they will do an exchange quite reasonably and take your old core.

I've seen lots of parts suppliers that would have a motor and a shunt on the counter so to test it they would just wrap the belt around it and run it while holding it tight enough for the belt to drive it. the shunt provides a load to prove it can overcome some resistance and actually output power. its a quick and simple test an alternator shop can perform for you while you wait, if you doubt yours.

those guys would be who I'd ask about fitting an adjustable voltage regulator if the problem is overvoltage.

I think the modern regulators use a solod state relay ( SSR) really old ones used mechanical contacts. the regulator is a small bit you can carry with you if you suspect issues or feel yours is old or perhaps nearing its end of life, Its good to change it just to have one less thing to fail on you

extracting and replacing the bearings, the bearings are standardized so I;d just buy bearings using the bearing number if yours fails, probably an alternator shop will have them under the counter too, and know which you need.

you may wanto change the regulator out on the road , pulling bearings is a bit more work. you may need access to a bearing puller. you can pack them with you and find a shop locally to help , should you have an issue on the road ..

i believe most cars will run a while without charging, if you have an issue you may be able to charge yours just to hobble on home.

my dad once had an issue with his in a Volvo 240 overcharging, his wipers started to go fast, headlights too bright, he tried turning everything he could on thinking it would help and he somehow got home anyway bit it fried some wiring up. pulling off he belt was likely the easy solution there. you can do that if it is a separate belt at least if you don't need headlights. the engine can run for a while on the battery alone, otherwise.

If I was stuck somewhere and bought a new battery, to continue I'd use the battery for something else so I wouldn't consider that a dead loss, a second alternator that you won't ever need, is.

Id be really careful if you start working on newer cars like BMW's and such they may have some more electronic complexity. If anyone ever asks me for a jump I make sure they know Im taking the cables off if it wont start and also that Im not taking any responsibility if they blow their ECU..

I did once pop an ECU in a Volvo 240 , a moment of stupidity got the charger or jumper cable bass-ackwards and I heard my ECU pop straight away so pay close attention that they are correct. Its an easy and fast way to make yourself feel really stupid ;-) luckily I had a spare but I sure wouldn't want to do that with some other persons expensive car. lesson learned.

[Monkey Wrench]

The other way to manage this is with a DC>DC charge controller between alternator and battery to set up a precise charging profile to keep your batteries healthy. I use one with a MB Sprinter-based RV with AGM chassis battery and LFP "house" battery which runs all of the living area and inverter.[/QUOTE]

I have an 88 ford van with a wheelchair lift which I don't actually use as I am not disabled.. I would however like to run a second battery and that could be arranged in such a way that the second battery is always maintained but I couldn't run it down by using the lift or for things like using it for camping.

If I loose my main battery it also provides a way out, I guess I could jumper myself or maybe there is feature to to that without disconnecting? the modern 110 invertors are also handy to run computers etc.
nice feature to fit a 110 V wall outlet even if output capacity is limited.

another thing I'd like is a battery quick disconnect to remove power drain from clocks etc. I often will park a car 2 months and its dead, this is not great for the battery life. Ill usually just pull the terminal off.

[Monkey Wrench]

normally an alternator puts out "dirty" power it is rectified so it is DC but the output is not filtered (no capacitors to smooth out the AC component)
i believe the alternator contains a diode or bridge rectifier that creates DC but not clean DC.

the wet cell normally acts as a filter , removing the ripple, which is then used by the ECU etc. the ECU probably wants more steady DC. Most power supplies will use capacitors to smooth out the ripple. In a car I don't think they are necessary.

a radio noise suppressor may be used to protect the radio from it, that's just a capacitor.

sometimes I see people put LED bulbs in and they can have an annoying flicker , it seems as thought they are sensitive to the ripple more than incandescent are because with incandescent bulbs there is a warmup and cool down period to the filament but LED's can act like strobe light. - faster response rate.


I don't know if the new style batteries are as tolerant of being charged with "dirty" power like the wet cell was. I think its likely they can still remove the AC component.. but there could be some related differences.

I think if I was converting Id want to know more about how this ripple current affects the new style batteries. its likely documented. maybe there is a tolerance of how clean the power may need to be? Does being charged with dirty power affect the new battery's lifespan?

the alternator's output could be filtered, using capacitors basically, but it may or may not be an issue.. If it is not an issue, then no point complicating it.

I believe that if you measure the output with a meter on DC it''ll show voltage if you switch to AC now you are measuring ripple current, on a scope you can look at the trace and see a bit more.. because that's a graphical representation.

power from a battery is DC wet cell is very clean, no ripple.. I believe the capacity of the battery is normally acting as a capacitor would and smoothing out that ripple..

it is also likely that inside the ECU, there may be some filter capacitors on the line in and on the circuit board ,, to protect it from the ripple current.

the ECU itself doesnt; use a lot or power so probably doesn't need big capacitors..

I did take apart the ECU of my ford van, looking close at the circuit board I could see the capacitors had outlived their useful life. I could see the electrolytic oil had slightly discolored the PCB board only in the area of the capacitors. th sis a sure sighn they have leaked.. Likely the other parts of the ECU have a longer life expectancy than the capacitors do..

this may make an ECU not work properly, and it is possible to replace them, they are worth about a dollar each or so . I suspect they are replaced if the ECU is "rebuilt" also a rebuilder may have a test bed to check its functions.

I think the other stuff in your car, wiring lights relays , motors is quite tolerant of a little bit of AC.. but the newer LED lights may not be.

a battery and a an electrolytic capacitor are electrically similar, they have a polarity , shoud not be hooked up backwards, they store and give off power, the capacitor just has a lot less storage capacity. the "amp hours" of a capacitor are very small normally thats measured in microfarads. the maximum voltage tolerance was about 16 volts.. youll see both if you look close at the markings. if the tolerance is higher that is normally not an issue.. the band marks the negative lead.. If you ever clip one out to replace it , note its polarity first

the one in my van did work and I accidentally clipped a transistor and just ordered a new one but I believe this could have prolonged its life otherwise. I found I could make my connections in the side of the capacitors so I didnt need to remove it and repalce the heat putty, I just clip them leaving a stub of lead, wrap the new leads around a pin so they look like spring, solder that to the stubs,.. if you preferred you could work on the solder side of the PCB and do the same. no difference electrically.

I think someone here is offering a service to rebuild an ECU and perhaps he takes it a bit further.. the only test most of us have is to put it in the car.. an electronics technician would understand the details in greater depth and also possess a proper soldering station and be better at soldering small things.

ive read some things about the microchips failing with age, I'm unsure about that, they are sensitive to a shock , or electrostatic discharge,, you can ground yourself while you touch them to prevent a static shock from you, from ruining them. wearing a wrist strap is common.

[Elynch924]

Not on the topic of the actual battery type but one post noted a pad with dried baking soda. I had purchased a battery pad years ago and used it in my 924. It was reported to prevent any leakage from the battery from attacking the battery tray. That noted... what I think instead happened is the actual pad soaked up water and then would be holding it between the battery and the battery tray. So I got rust anyway. So pads or no pads?

[wwdwgs]

Elynch924 - better to keep the area dry. It's a little hard to fit a plastic tray in that area, given the clamp-down method Porsche used. i think that the plastic tray will be better.

[Monkey Wrench]

ive seen lots of cars with rusty battery boxes, although batteries are generally sealed somehow acid gets out.

i just soak a cloth in baking soda and water let it dry, and place it under my battery that way any acid gets neutralized immediately.

ive never had the issue of the pad becoming water soaked and retaining water.

in a former life I had to maintain electric forklifts , they have huge lead acid batteries that can be swapped out. part of regular maintenance was to give the outside case a wash with a paintbrush and baking soda and water. also wed check the specific gravity and add distilled water when needed..
that way you aren't wrecking your clothes or walking away wondering why your arm is burning , or replacing your pants due to holes.. most of us here have probably wrecked some clothes that way at some point.

also I lake to keep a box onhand. its cheap and can neutralize an accidental spill.
gel cells or similar that aren't vented and are well sealed may not need the pad I guess.. If I spilled acid I'd run for the box..

I think most lead acid batteries, although they may not have easily removable caps like older ones, still need some sort of vent, so they can't explode by pressure building inside when charging or by expansion and contraction with temperature changes.. and things like that. the acid may leave slowly that way.. maybe just by air within moving to outside the case. I guess some have a vent for that.

Do what YOU prefer of course, but thats my way .. I don't need any special pad, just a face cloth will do.

if you think the battery compartment gets wet because its near the vent cowling etc, maybe that is a different concern.. my suggestion was not to add a wet pad, let it dry out first. I've been keeping my 944 in a tent so its not wet and that was not a concern but I do think I remember it had a drain hole around the compartment somewhere.. maybe its susceptible.. my compartment looked decent , not rusty when I got mine and it sat outside a lot before then so it didn't look like a wet area to me. Here
In vancouver there is no shortage of rain lol..

[BadToTheBown]

I was an early adapter which didn't go so well. Started with Shorai where the early units didn't have built in BMS (Battery Mgt System). Later ones did, which was huge to their longevity. They are way lighter BUT plan on putting them on a charge specific, or configurable, for this specific battery tech. Occasionally (maybe once a month) put that charger on no matter how good the battery is working. IF you don't, you risk developing a cell with lower charge memory and then one day it's won't work, that quick. I use AGMs now because it's simpler and charges best in older car charging systems but if you really want it, charge using the battery's BMS system as it charges all the cells individually to prevent a low cell memory...just what I've done and think...

[Monkey Wrench]

what Id do is go to a battery shop , I have one local and all they do is sell batteries which makes them basically experts.
I think its feasible to regulate the maximum voltage and to apply additional filtering so maybe they can just basically sell you a little box designed to do that, to charge the sealed batteries but first to condition the power on its way to the battery from the alternator.

its a bit unrelated but I have a 88 ford van with a serpentine belt that seems really susceptible to setting itself off and squealing loudly and have replaced most related parts more than once.. its worse in cold because , well its likely sat a while and needs a good charging upon startup.

I think the regulator works by tripping in and out using a solid state relay and in turn maybe connecting or disconnecting the field windings. this all happens internally to the alternator.

Ive been brainstorming and thinking gee if I could just turn off charging until it reaches its warm up , thermostat open, and then triggers charging maybe that would help ,as then the belt could warm up and demands on it would be a lot lower. I think it is quite loaded when battery voltage is low..

its a bit of a convoluted way of fixing what should be a simple issue. I figured that maybe once it is warm , maybe there is an output from the ECU that turns on and maybe that could trigger the coil of a relay to turn charging on.. maybe with an override switch.

that way the charging would start after warmup and maybe not set the squealing off so much.. there is an upgrade to a wider serpentine but its 2000 dollars, That's too much for this guy. It my suit hot rodders , some use it to drag race with etc.
lots of trucks use the ford 300 L6 and most do not report this belt slippage issue. Ive been going through tensioners belts, new alternator water punp, nothign seems bad or misaligned or loose or wrong. - anyway thats all off topic.

the porsche will have a v belt and it needs to be tight enough its surprising what a load the belt is under with a low battery.

it suddenly occurred to me that if the car or truck can actually warm up without trying to also charge the battery at the same time . that this could be beneficial , what it is actually doing is demanding power from an engine that's not warm yet. I figure that during driving there is normally plenty of time to catch up..

I think when the car starts what you do have is a little situation where the charging system is demanding, even during cranking but I guess its was never enough of a problem for any automaker to try to wire around it. its a bit of added complexity and perhaps an unrealistic idea, but I don't see why it would not work in theory. ..

the alternator puts out DC power, yes it may also have a lot of ripple current. it is possible to convert that to AC 110 with an invertor, you could then run a charger off an invertor but that's just way too complicated.

I think what you want is sort of an in line power conditioner to provide a more stable voltage, to protect the delicate charging needs.

I thik if someone wiht an electronics backgrounbd looked at the issue they could design a little board with some filtering and also limit the maximum output but no point reinventing the wheel I don't doubt you can buy this off the shelf..

I remember trying to understand how a zener diode works as I know they can be used to limit current above certain voltages but Im completely unsure if one would be helpful here, an electronics technician would be able to solve that with a deeper understanding. for all I know maybe its part of a new style solid state battery, since the battery needs protection , perhaps it is included by design?

Bad to the Bown lamented that the figures the AGM batteries were more tolerant than the Shorai.. maybe AGM documents the power required so you have a target to work towards.

I'm thinking maybe you can get alternators with a built in power conditioner but maybe it can just be a separate item, that might be cheaper than buying a whole new alternator? the one you have makes enough power so the issue seems to just be in making the power more "carefully" regulated.


some of these battery companies may have good customer support techs involved.. so I'd maybe try calling them, read any specs you can first, then call and ask what sort of power conditioning would be suitable. see what the particular manufacturer says to do? Im sure they are in a financial position to want to see projects like this succeed. Success by one leads to future sales for the next. They won't want a bunch or reports about early failures. or worse, fires !

some older cars had the regulator separate, earlier volvos were like that but I thik with modern electronics this can be done with IC's not old fashioned mechanical
contacts like were used back when generators were used. It sounds like you want to filter the ripple and limit maximum voltage. I dont think thats an insurmountable problem.
personally I wouldn't go replacing the alternator until I knew a bit more about what is needed to do that.

for me the issue seems to be non use time so maybe the deep cycle ones are ojk for that as they are designed to tolerate being drawn down and refilled more than a regular car battery.

the other thing I've done personally is don't buy a battery for every car, 6 is too many. that's why I add a bit longer leads to make that easier, then I don't care watch side is positive. if the battery will drop in , it will work ok . The porsche is special needing a shorter battery. in my van the compartment size is also restricted, volvos can seem to take almost any older style battery, with "normal" posts. if I put them in the house then I need to carry them out to start them , it is nice to be able to not need to do that just to get the fuel going and not sit too long. plugging them all into conditioners is too many cords, too many conditioners too.. So Ill move my big charger and put it on 4 hrs every couple months. pull the posts off in the meantime.