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Old 06-24-2012, 05:56 PM   #3 (permalink)
Ryland
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Quote:
Originally Posted by yugomodder View Post
Do flooded lead acid batteries need vents/fans or can they be kept in an airtight box? I've heard that they produce hydrogen and that this needs to be vented out, which makes sense. On the other hand there are sealed, gel, and AGM batteries that don't seem to need to be vented.
Yes, flooded lead acid batteries need to be vented, if you have them inside of the vehicle then using a brushless motor (no sparks) fan is a good idea, you don't need a lot of air to be pulled out but creating a weak draft is a good idea to prevent a build up of hydrogen and to keep the vapors from the acid from collecting where you don't want them.
for sealed gel or AGM batteries they still have vents but they tend to be sealed vents or valves that are there as a safety to keep the battery case from exploding, over charge a sealed or AGM battery and you will blow the vent caps and end up with some lead to take to the scrap yard.

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Would lead acid batteries benefit from a BMS? I know that it is necessary to have one for lithium batteries. If a BMS would extend the life/increase the performance of a lead acid battery pack, then it might be worth adding.
Yes, one of the developments that has increased the life of lead acid batteries is battery management systems for lead acid, this can be as complex as an automated system that puts the car in to limp home mode when the batteries get low or it can be as simple as what I have, a PakTrakr gauge (no longer made) that gives you a read out for every battery in the pack and looks for batteries that are lagging behind or are acting like they need water or maybe have a bad connection, I've also seen a friends lead acid BMS that was made by Quick Charge that shunts power past a battery once it is full these were designed for sealed lead acid batteries but in theory should keep the vents from popping, with my battery gauge I can extend my battery life by see that one cell is falling behind and I can check that battery over and maybe put a 6v charger on just that one battery in the pack to bring it back up to where the rest of the pack is.
Either way, a battery management system that keeps the batteries happy will add time and cycles on to their life!

The other important thing that you did not bring up is smart chargers! my old charger was a big transformer that as the pack reached it's full state the charger would level off but keep charging, my new charger is a solid state switching power supply charger that is programed to do a bulk charge where it's just dumping energy in, then it brings the pack up to a set voltage and hold it there for absorption, then drops back and does a float charge and after a bit shuts off, kicking back on if the voltage drops to low! a smart charger like that should extend the battery life while giving you the most miles per charge because the pack is not 99% full, it's 100% full without having been boiled to much.

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These next questions will deal with Lead Acid battery life/how to extend it.

Typically lead acid batteries last for around 500 charge/discharge cycles. How can we extend this, and how far? To my knowledge lead acid batteries are completely, or almost completely recyclable. If this is the case, what causes the batteries go bad? Is there any way to reverse, or partially reverse this without completely disassembling the batteries, and taking them back to their base components.

What are factors that contribute to the degradation of lead acid batteries? Lets try to look at this both chemically, and practically. Sulfation of the electrodes seems to be one of the main, if not the main factor contributing to lead acid degradation. Sulfation of the electrodes happens from the acid reacting to the lead plates. Sulfation happens most quickly at low states of charge.
If you can figure that one out, then you might make it rich, because at that point you would have lead acid batteries that last forever! battery makers say there is nothing you can really do other then keep them watered and keep them charged, people I know who install off grid systems say the battery desulphaters do help, they give a high frequency pulse to help prevent and reverse build up of lead sulphate, I have a device like this on my electric car and have a 3 year old pack that still has 35 miles of the 40 mile range left, I also have one on my electric forklift at work and it's not gaining life but that forklifts 10 year old pack is not showing further signs of aging.
I don't know of anyone who has done a blind test of a device like this, but I also haven't been able to find anyone who can say that a device like this causes harm or shortens the battery life.

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On the other hand, even a small charging voltage applied to the batteries is supposed to completely stop, or vastly slow down sulfation. What rate (preferably in C) is needed to do this?
Again, I'm not sure on the charge rate that is needed, but would be the one advantage of putting PV panels on an electric car, even tho the solar panels wouldn't add more then a mile or two per day to the range, it would be adding a trickle charge to a battery that might otherwise be sitting half charged at work (day time) but as I understand it, any activity in the battery is good and that is where the desulphator is also supposed to help, it does the pulsing by charging and discharging a small capacitor, so it's chemically keeping the battery active.

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A clever solution proposed by many, is to use a small capacitor to help level out the load on the batteries.
Apparently if you hook up an osiloscope to the battery and watch the voltage, the PWM speed controllers cause a ripple in the voltage, of course there are some capacitors in there already to smooth out those ripples but as I understand it (correct me if I'm wrong) most of those capacitors are on the output side to give the motor a smoother, ripple free flow of electrons, but that drawing power off the batteries in pulses drains them down faster then if it was a smooth resistance load, so even adding a modest sized capacitor should help extend your range, I'm not sure how Fared compares to Amp Hours, but one guy I was talking to said he was planing to use a 2,000F capacitor to smooth out those ripples, this would be a soup can size.

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I've heard that flooded lead acid batteries have to be "watered". How is this done, and how often? Would it be possible to make an automated system to maintain the batteries constantly at the proper level?
To water batteries you open the caps up on the top of the battery and add distilled water, there are battery watering systems out there, one draw back to most of them is that they can freeze, so they need to be drained after each watering, they also have floats that can bounce as you go down the road so you need to disconnect the water supply after each watering, but the big advantage to them is that you can have your battery packs in locations that are harder to get to, I for example have to get out a turkey baster and mirror when I water my batteries so I can see how full they are and squeeze more water in to them, the battery watering system I just bought will allow me to hook up a plunger pump to a jug of water once a month and fill them, the floats then stop the flow as each cell fills to it's correct level.

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One of the main ways that I see to extend the life of a battery pack, is to simply make it larger. A battery pack twice the size, should last far more than twice as long. This is because all loads placed on the pack are halved.
That is a nice idea... but can you do it? my electric car weighs 1,400 pounds and 530 is lead acid batteries, I notice a change in performance when I have a passenger in the car, if I added another 530 pounds of batteries it sure would help with range but as you pointed out, I'd need a large motor and a larger car and suddenly I'm not driving a 1,400+530=1,930 pound car but I'm driving closer to a 3,000 pound car because I need tires with a higher load range, springs that can handle more weight, a frame that can handle more weight, a larger motor, more battery cables, larger battery box, a larger speed controller to handle the increased power.
The one area that you can add more batteries is in an off grid house, my parents expect to get 20+ years out of their off grid battery bank because they sized it so they only have to use the top 20% of the pack, the pack never moves so it doesn't matter how heavy it is.

My goal for my electric car is to replace the lead acid batteries with Lithium in a few years when my range is down to 20 miles or less per charge, I might even go with lithium batteries on my motorcycle as I need to figure out a good battery for it, the advantage of lithium is that you get 2,000+ cycles out of them instead of 500, you can drain them deeper and faster without damaging them and because they can quickly discharge more of their energy without the same losses you can get more watt hours per mile out of lithium batteries, then they are lighter so you have better performance while drawing fewer amps so once again you win! and big reason for lithium for me? I can buy a used set for $800, while a new set of lead acid would cost me $720 for the same usable watt hours worth of battery.
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