Battery discharge question

[taylorp035]

If you take a lead acid battery and discharge all the way to say 95-100% and then start to recharge with in a few minutes, will it hurt the battery significantly?  More or less, could you take it to ~11.0v and then recharge it immediately with minimal effects?  Our supermileage car would use a 9ah battery to start the engine ~25 times, but sometimes we would do two runs, so a total of 50 starts, which would completely drain the battery.  After that, we would charge the battery immediately.  I was wondering how much damage we did to the battery.

I did do a test on that particular battery, which had been used for 3 years, and it had at least 5.5ah's in it.  I'm not sure how many more amp hours I could squeeze out of it, but probably not many.

I am curious for the answer to this question because I don't get to work with lead acid batteries very often.
I end up replacing the battery in my 4-wheeler every 1-2 years due to it's extreme environment.  I take it out during the winter and charge it every month, same with my lawnmower too.
For my supermileage car, we are thinking of purchasing a 80-100ah battery for off grid battery charging of our lipo and life starter batteries.  I have my 400/750 watt inverter and we have our battery charger that runs off of 5-30v dc, so it would be nice to have portable power.  My concern is that purchasing a Pb battery that gets used only once a year may not be a great idea.  We could charge it every 3 months, assuming people remember to.  During competition, it would be drained down by 20-40 ah and then recharged at the end of the day.  Loads would be upwards of 30 amps for the charger and possibly up to 40 for the inverter.

Recently I have been looking at the new 65/130 C lipo thunder power batteries.  They claim an impressive 12c charge rate, which means only 5 minutes!  I have charged at 4c and 5c with my current Life and Lipo batteries, but they do tend to get warm (the life batteries).  The lipos stay cool all the way to the end, which impressed me majorly at 5c.  The interesting part is that the new 65/130c batteries are the same price as my 30/60c cells.  Things like this excite me, especially when you think you can start our engine off of a 800 mah battery or less... (our starter pulls only ~30 amps continuous).

Sorry for going so far off my question, but there was a lot of things to say 


TaylorP035

[SparWeb]

If I understand what you're saying, you estimate that your 9A-hr battery would be completely drained if used to provide 50 engine starts.  Under some conditions, it will only be expected to start about 25 times in a day, at the end of which it would be recharged.  The light-duty day drains it 1/2 way but those long days will run it totally flat.  I take it that you are using a compact sealed lead-acid battery to do this, and that space is limited, otherwise you could get a larger one or a second battery, and that there's no means to recharge it while on the road.
Do you have to be concerned about not being able to start at all?  When the charge is low, the voltage drop gets so low when the load is applied that the starter may not work at all.  Starting a warm engine is easier than starting a cold one, so the energy consumed per start will be variable.  I guess there's no easy answer so I can't anticipate how much battery you need in your car.

IMHO, the long-term life of your battery, nor your car for that matter, is of great concern if it's only supposed to survive the supermileage competition.  So what if it's drained flat several times?  It will recharge almost all the way back, if not fully.  The things that will harm it the most during these deep discharges are the things you must avoid for safety's sake anyway: don't get it too hot, don't recharge it too fast (also a temperature problem).   Your gut-feeling is correct that deep discharges are harmful, but pushing an item to 100% capacity can be justified in competitive terms, because once it serves its (brief) purpose, you don't have to worry about its longevity under those conditions.  Competition rules and your team's budget can limit how far you can go with that attitude, though.

[Flux]

Lead acid batteries are far from perfect and the last 100 years of evolution hasn't changed them a lot.

What you do to them does have a significant effect on their life but when you get outside the normal operating range the various types and makes of battery may behave differently. Normally there are only a relatively small number of discharge cycles in a lead acid battery and this depends a lot on the construction. I suspect that for something like a car battery it is not much over 100 cycles in normal use. That would give you 1000 cycles at 10% discharge and normal car starting doesn't drain that much.

If you take them to 11v and recharge immediately with correct charging procedure you probably won't reduce the number of cycles drastically, but it will certainly fall. This is assuming a rapid discharge to 11v. if this discharge is over a prolonged period then I suspect sulphating will take its toll if you do this many times.

Taking it to dead flat is much worse and you may not get many cycles at all and at the end of a complete discharge you will have trouble provoking it to start the charge cycle at all as it will be fairly well sulphated .

There is additional problems with shedding active material from the plates, I am sure this will happen badly if you go much below the 11v from a rapid discharge.

I suppose what I am trying to say is that a rapid discharge to 11v doesn't take it to 100% discharge, its probably near 80% and although bad it will probably still manage a reasonable number of cycles. Going much lower will shorten life very drastically.

There is not a lot of useful charge left beyond 80% discharge and normal loads won't benefit much from it so your lower limit will be much as sparweb has indicated and decided by practical issues.

Batteries die if you use them , they die if you don't, so if you can get the result you want by abusing them then it may be fair game. I am pretty sure that some units will stand it very much better than others and sadly the cheap ones that you could afford to risk it on will be the least capable of handling it.

I have used car batteries in applications where I should have used leisure batteries ( leisure batteries are a recent thing anyway) and as far as I can tell the best car batteries well out perform the poorer leisure ones even when taken down to about 70% over a period of 2 days.

The best way to compare two batteries that claim identical specs is to weigh them, the heavy one will do the work, the light one will give up almost invariably, you get what you pay for in the end.

Flux

[joestue]

If you take a lead acid battery and discharge all the way to say 95-100% and then start to recharge with in a few minutes, will it hurt the battery significantly?  More or less, could you take it to ~11.0v and then recharge it immediately with minimal effects?  Our supermileage car would use a 9ah battery to start the engine ~25 times, but sometimes we would do two runs, so a total of 50 starts, which would completely drain the battery.  After that, we would charge the battery immediately.  I was wondering how much damage we did to the battery.

I would buy a 17 or 20 AH SLA if you can afford the weight.
or you can cheap out and buy a 25$ lawnmower battery at wally world
i'd speculate that 9 ah battery will last  for about 250 engine starts, max

[ghurd]

Considering the cost of the project, might stick with a ~7AH... and get 2?
Switch them out at the 25 start mark.
G-

[taylorp035]

Ok, as I suspected, using a lead battery for the competition isn't necessary a bad idea since the life span only needs to be about 2 days.  Recharge time can become an issue, as last year we did 6 runs in a day, totaling 150-200 starts.  To make matters worse, we don't necessarily have access to power.

Now, this was the solution for the previous year's supermileage cars, which was very bad.  This year's car will feature ~ 4.4 ah LiFe battery.  By swapping out the starter motor and battery for smaller and lighter batteries, we shaved off over 10lbs, which means another 30-40 mpg.  Since our budget is almost limitless, we could spend $130 on some of those extreme 65c batteries and get a 5 minute charge time.

The nice thing though is that just about everyone can charge a Pb battery, but most people will screw up charging a Lipo battery.

[Rover]

Maybe someone has posted this already, but can you bring a  spare battery to the competition charging it externally  and  swap out  as needed? or does it have to be self contained on the vehicle?

[taylorp035]

It's not that I don't have good solution for the car.  My original question was if I was ruining my Pb batteries, which has been answered as a "maybe so", but "it doesn't really matter".

For the competition, our plan is to use small LiFe batteries with Anderson Power Pole connectors that can be swapped out quickly between runs.  Currently we have (4) 4s A123 packs, so we can run them either as (4) 4s packs or (2) 4s2p packs.  We may also have a separate battery for our cooled seat, which may require a good 200 watts while running.

The a separate 4s LiPO4 battery will run the electronics fuel injection system (the computer, the coil, and the pump), which uses all of 3 amps for 3 seconds per engine fire.  Since we have 1.4 ah to accomplish this, we could also use the power for something else.  I initially wanted an electric supercharger with a 1000 -2000W electric ducted fan, but that would require some modification and it is questionable if that would help at all.  Option number two says we go with an hybrid turbo, where an electric motor would get it up to speed before the engine turns on.

[tanner0441]

Hi

I don't know what the course is but could you afford the weight of a small alternator and put some charge back in on braking and down hill?

Brian

[taylorp035]

We don't use our brakes... but your idea is a good one.

Also, we will have plenty of juice in the batteries to make it around the track.

[Bruce S]

The only worry I would have would be the high instant current needed for the starts, and the batteries abilities to recover quick enough.
The LiFe and LiPo batteries you're looking into using, do they have the C/drain abilities? can they even give up that much instantaneous drain?
By removing the starter motor what are you using to replace it ? or was the starter/SLA batteries versus starter/LiFe batteries make up the weight difference?

Keep going with the posts when you have time, this is truely awesome to watch unfold.

Cheers
Bruce S
 

[zap]

The only worry I would have would be the high instant current needed for the starts, and the batteries abilities to recover quick enough.
The LiFe and LiPo batteries you're looking into using, do they have the C/drain abilities? can they even give up that much instantaneous drain?

Some video using A123 for starting a vehicle.
http://www.youtube.com/watch?v=qcvmvrmTMMk  and a better picture of the pack here:
http://hackedgadgets.com/2009/01/19/jumpstart-your-car-using-some-a123-batteries/

[Bruce S]

The only worry I would have would be the high instant current needed for the starts, and the batteries abilities to recover quick enough.
The LiFe and LiPo batteries you're looking into using, do they have the C/drain abilities? can they even give up that much instantaneous drain?

Some video using A123 for starting a vehicle.
http://www.youtube.com/watch?v=qcvmvrmTMMk  and a better picture of the pack here:
http://hackedgadgets.com/2009/01/19/jumpstart-your-car-using-some-a123-batteries/

Zap;
 Thanks for the links, pretty cool!

[zap]

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You've just spent 20 minutes climbing to the 500 foot level of a transmission tower.  You find a midpoint microwave antenna bracket has cracked and needs repaired.  The welding rig is on another job over 200 miles away...

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[taylorp035]

The only worry I would have would be the high instant current needed for the starts, and the batteries abilities to recover quick enough.
The LiFe and LiPo batteries you're looking into using, do they have the C/drain abilities? can they even give up that much instantaneous drain?
By removing the starter motor what are you using to replace it ? or was the starter/SLA batteries versus starter/LiFe batteries make up the weight difference?

The C rate for the A123 LiFe batteries is 30C / 60C, which 30 is continuous and 60 is for 10 seconds.  They are 2.3ah and 3.3v nominal.  For 1 second, it is about 100C, which drops the voltage down to ~2-2.2v.

The LiPO4 batteries we have currently are also 30C/60C.  There are new ones out there that do 65C/130C and have a 12C charge rate (5 mins  ).

You can start a car with a 4s2p pack of these easily.  I attempted to do so with a 3s3p pack, but the voltage was too low and I had a bad connection.

I started my lawnmower and 4-wheeler with a 4s1p pack.


As for the weight difference, the old motor and battery each weighed 6 lbs.  The new motor weighs 0.5lbs and the battery weighs ~ 70grams * 4 cells ~ 0.5 lbs.

[Bruce S]

Zap & Taylorp036;
 Thanks for the info on the A123's I may have to finally invest (i.e. purchase some batteries) This would be very interesting to work with.
I am still gathering knowledge to build my next 3-wheeler possibly hybrid.
I truly enjoy riding my 150cc scooter and the fuel savings i get, but arriving at work soaked because the rain gods needed a good laugh is only funny once.

Here's a picture of the 36Vac trike that is my current source of inspiration.



It's power plant's are 7 speed shimano and yes a 36Vac 600w motor. The batteries are rebuilt NiCd packs arranged in 14.4Vdc 20Ahr packs  6 sets total for 40Ahr range.
Comes complete with folding windows a wiper and full set of lights. since the NiCds weighting in at 115lbs which replaced 200lbs of SLAs that only gave us 36Ahr and would die under the deep discharges you can see where saving weight and help.

[ghurd]

How far is "14.4V... for 40Ahr range" for us regular people?
It does not sound very far with a 600W motor.
G-

[zap]

It looks like it has "AERO" on the nose.  Is it a "one off"?  2005 picture date... still made?

That belongs to the company you work for?

[Bruce S]

How far is "14.4V... for 40Ahr range" for us regular people?
It does not sound very far with a 600W motor.
G-

G-
Sorry should've made that more clear. The packs are arranged in a 36Vdc times 2 for the 40Ahr set total.

It is even with the batteries the trike still lift-able by 3 people.
On a full charge it can go ~18 miles IF the rider/peddler uses the bike side to take off from a dead start, this is on streets that are not flat.

We also found out the hard way that the 12Vdc sags under a real heavy load, even when setup as 36Vdc it still sagged, going to the 14.4 kept us with in the voltage range the motor and controller could handle. According to the German manufacture, the motor can handle 48V, but I didn't want to push it.
 

There's a 12V setup not attached to them for the lights & wiper motor.
Bruce S

[Bruce S]

It looks like it has "AERO" on the nose.  Is it a "one off"?  2005 picture date... still made?

That belongs to the company you work for?

Good eyes,
Yep, it is still built, not a one off either. They are still building
 Here's the website http://www.aerorider.com/ don't go into sticker shock when you see the price tags though.
If you google the aerorider you should get lots of hits for them here in the US too. Ours was on bentrider for a while back when it first came in.

Yes, it belongs to the company (biomedical systems www.biomedsys.com)
We used to do the sanctioned chili cook-offs when they were still doing them here in St.Louis, and this was the draw to our tent .
During the heatwave I had inside the canopy every SLA I could grab from old UPSs and had them attached to different inverters and DC powered fans.
The batts were toast anyway so using the last little bit for people cooling was worthwhile, like the Joulethiefs being built now.

Bruce S
PS> I'm going to put more info over in Transportation so We don't hyjack Taylorp035's thread.

 

 

[taylorp035]

Well, if you have any questions on the batteries, please ask me.  If I were you, I would go with a brushless out-runner motor for model airplanes, maybe the 1500w-2200w himax motors.  An 800w motor would work, but I wouldn't want it over heating on you with the minimal amount of cooling.  Add a castle creations brushless controller (mamba monster possibly), and you would have a nice and very efficient set up.

If you do end up buying some A123 batteries, they will run you about $7-8 cell on ebay.  You do need to be careful charging them if you don't have the right charger.  The voltage likes to shoot off like a rocket when they get to the end.  The nice part is that you can charge them quickly and discharge them all the way down to 2v, so you get 2000+ mah out of them.  As far as I am concerned, the capacity never goes down, and I was using them in my combat robots under some pretty extreme situations. 

They are pricy, but I once saw a guy who ripped apart a prius plug in hybrid pack that was made of a123 batteries.  He was selling them in 2s11p packs for $88, which is a steal at $4 a cell.

Just don't waste $179 for one of those new 36v dewalt packs.  I have bought my 3 packs for $85-100, each containing 10 cells.


Another option for your drive system would be the new 5th scale monster truck brushless combo by CC.  It's a little pricey - $600, but you get something that is good for 10 hp continuous.  it also has easy to use data logging, which could be helpful on a project like this.
http://www.castlecreations.com/products/mamba_xl.html

[dlenox]

Taylor,

Have  you considered putting on some type of solar panel to help recharge the battery between starts?

Dan Lenox

[taylorp035]

You could, but I bet any solar panel would be heavier than a lipo battery.  Also, you would probably only get 50% of the rated power out of the panel, since you are changing directions and some of the track is shaded.

[Bruce S]

Well, if you have any questions on the batteries, please ask me.  If I were you, I would go with a brushless out-runner motor for model airplanes, maybe the 1500w-2200w himax motors.  An 800w motor would work, but I wouldn't want it over heating on you with the minimal amount of cooling.  Add a castle creations brushless controller (mamba monster possibly), and you would have a nice and very efficient set up.

If you do end up buying some A123 batteries, they will run you about $7-8 cell on ebay.  You do need to be careful charging them if you don't have the right charger.  The voltage likes to shoot off like a rocket when they get to the end.  The nice part is that you can charge them quickly and discharge them all the way down to 2v, so you get 2000+ mah out of them.  As far as I am concerned, the capacity never goes down, and I was using them in my combat robots under some pretty extreme situations. 

They are pricy, but I once saw a guy who ripped apart a prius plug in hybrid pack that was made of a123 batteries.  He was selling them in 2s11p packs for $88, which is a steal at $4 a cell.

I will certainly keep you in mind.
The pic maybe a bit misleading due to the helio-wing on top .
This is a full sized person inside riding out of the rain sized buggy.
The wing was up there for Halloween :-) There's more pics showing it lit up and a rat ( fake being cooked on a fire spit ( also fake) but we won 1st place with it.
Most of the pics may not be PC tho  .

I have a neighbor whose Hybird Camry is due to give up it's getting old battery pack.
He's hooked on his solar panels setup , so we may have to do a small horse trading. I think those are still NiMh types.

Thanks
Bruce S

[MagicValleyHPV]

Just don't waste $179 for one of those new 36v dewalt packs.  I have bought my 3 packs for $85-100, each containing 10 cells.

I bought 5 Dewalt DC9280 (28v) on sale last year from Tool King for $50 ea + free sh. These are 8 x 26650 A123 cells. Currently they are $80 ea. No idea if they will discount them in the future, but you might wanna check their site occasionally.   

http://www.toolking.com/dewalt-dc9280-28-volt-lithium-ion-nano-battery