# Charging lead acid using alternators?



## Sunking (Aug 10, 2009)

The big issue is going to be efficiency. The first loss is the AC motor as their efficiency ranges from 60 to 95%. Next in line alternator efficiency, then last the battery charge efficiency. By the time you get it all added up you could very well be pumping in 4 wh to get 1 wh out.


----------



## ken6881 (Oct 7, 2011)

Sunking said:


> The big issue is going to be efficiency. The first loss is the AC motor as their efficiency ranges from 60 to 95%. Next in line alternator efficiency, then last the battery charge efficiency. By the time you get it all added up you could very well be pumping in 4 wh to get 1 wh out.



thats the only down fall we seen (we were looking optimistically at 50% loss) which is not a huge deal because its only 7cents a kwhr here. 

Our other thought was looking at using solar charge controllers. but using 12v computer power-supplies(free from land fill I know a guy who works there) to power them instead of a solar panel. has anyone tried this? it would make it about 20 bucks to charge 2 batteries. 

thanks for your reply


----------



## Sunking (Aug 10, 2009)

ken6881 said:


> Our other thought was looking at using solar charge controllers. but using 12v computer power-supplies(free from land fill I know a guy who works there) to power them instead of a solar panel. has anyone tried this?


I work a lot with solar charge controllers.

Today they come in two flavors of MPPT and PWM. I think you can cross MPPT controllers off the wish list. PWM might work but I an not sure how that would interact with a ATX switch mode power supply. As long as the PWM is in 100% duty cycle I do not see a problem as at that point they are just a short circuit with a little resistance of the FET's. But once the battery approaches full charge and the PWM duty cycle is less than 100% I have no idea what would happen.


----------



## piotrsko (Dec 9, 2007)

yup it would work, BUT (caveats figure about 5hp for each alternator, Lossy as heck, and you probably will end up cooking your batteries somewhat unless you watch them carefully. a CV power supply ain't all that hard to make or all that expensive if you don't need mucho charging amps.

You will need to mod the PC power supplies as they tend to supply 12VDC and you will need at least 13.1vdc. They also get squirrelly at low currents they aren't rated for.


----------



## ken6881 (Oct 7, 2011)

Yeah we have looked at lots of options and I have some experience with CV power-supplies (electrical engineering class in college) but we are looking for around 10 amps +- to get a reasonable charge time. 

sunking 

That helps narrow down that search alot. We were hoping to use solar controllers because of size and being able to charge while at work or a friends house. the only reason we were looking at alternators was the high amp out put and price at $10. I think we will just order a solar controller and see what happens. 

here is what we were looking at and its a pwm so it looks like it will work http://www.ebay.com/itm/300616243178?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

I have used pc power-supplies to power dc to dc chargers in hobby use so i was hoping this would be an easy way to get power to the solar charge controllers. 


thanks again


----------



## Sunking (Aug 10, 2009)

ken6881 said:


> sunking
> 
> That helps narrow down that search alot. We were hoping to use solar controllers because of size and being able to charge while at work or a friends house.
> 
> thanks again


You are welcome. Like I said MPPT will not work because they are designed for variable current sources, not voltage sources like a puter power supply. To be honest I am not sure how a PWM controller will interact with an ATX puter PS.

With that said I have extensive experience with FLA and all lead acid batteries. I specialize in DC power plants used in the telecom sector. The easiest, safest, and best charging algorithm for long life for all lead acid chemistry batteries is the float constant voltage with limiting current to a range of C/12 to C/8 with C/10 being generic sweet spot. If using AGM you can go as high as C/4 charge rate...

So for bare bones reliable charging you want to find a power supply source that can supply the appropriate charge rate between C/12 to C/8. Example if charging a 100 AH battery then you would shoot for a 10 amp supply. Then use a precision voltage regulator to regulate the voltage to the ideal float voltage. For FLA 2.2 volts per cell is ideal.

Additionally if using FLA batteries you would want an EQ voltage option of 2.3 vps when required. If using gel (God I hope not gel) or any other of the various VRLA types like AGM, no EQ should ever be used. 

So my recommendation for a frugal quality charger is; 

1. Use whatever crude power source like an alternator or ATX PS with appropriate charge current rate
2. Employ a good cheap linear precision voltage regulator. They are very easy to design, build, and require minimum cheap parts.

There is only one disadvantage of float chargers with respect to lead acid batteries. They are not the fastest or most efficient algorithm. To obtain maximum speed and efficiency requires a 3-stage algorithm of Bulk, Absorb, and FLOAT.

Good luck

SK


----------



## MN Driver (Sep 29, 2009)

I was hoping that underlined text was a link explaining it, other than the application using alternators, what's wrong with using gel? I thought they weren't too bad as long as their max voltage wasn't exceeded so that gas voids developed. I'm curious because I was at an EV club when I as traveling out of state that had some people with pretty impressive lifespans using gel, meanwhile locally here we've got someone being gingerly with AGM and doing everything to not overcharge them and having pack death in 2 years and a year with their most recent pack. Granted it's a bunch of YMMV but I'm curious about your opinion since I'm not of the lead-acid persuation because of my range, size, and weight requirements for a small EV.


----------



## ken6881 (Oct 7, 2011)

Sunking said:


> Additionally if using FLA batteries you would want an EQ voltage option of 2.3 vps when required. If using gel (God I hope not gel) or any other of the various VRLA types like AGM, no EQ should ever be used.



Well I have to ask why not gel? We actually have a supplier for really cheap Alpha Cell (gel cell) batteries however we haven't pulled the trigger on the entire pack yet so it will be easy to go to FLA. I was under the impression that gel would not be an issue and would be low maintenance. 

also what does EQ voltage mean?

thanks

Kenneth


----------



## Sunking (Aug 10, 2009)

ken6881 said:


> Well I have to ask why not gel?


Gel batteries have one advantage in that they will not leak when installed other than right side up or even with a broken jar. However they have some disadvantages that should be of concern. The electrolyte has silica added to make the electrolyte turn into a solid mass very much like Jello. They must be slowly charged, C/20 or less, to prevent from gassing and drying out of the electrolyte. If over charged or charged too fast will cause cracks and voids in the electrolyte which cannot be reversed and the damage is permanent.

Secondly they must be charged at a lower voltages, about 2/10th lower than FLA or AGM, again to prevent form drying out the electrolyte. If you need the advantages of sealed batteries, then use AGM. 




ken6881 said:


> also what does EQ voltage mean?


EQ = Equalize. FLA batteries need to be periodically have a EQ charge applied to them. EQ does not apply to any of the sealed batteries like AGM.


----------



## ken6881 (Oct 7, 2011)

well looks like we will switch from our plan and go FLA. And hopefully use solar charge controllers to charge them. The plan is to get one and see what happens then go from there.


----------



## Sunking (Aug 10, 2009)

ken6881 said:


> well looks like we will switch from our plan and go FLA. And hopefully use solar charge controllers to charge them. The plan is to get one and see what happens then go from there.


What you might want to consider is buy a very small affordable PWM controller and use it as an experimental toy to see if it works or not. If it does not work, you received an inexpensive lesson. If it works them buy a large one.


----------



## ken6881 (Oct 7, 2011)

Sunking said:


> What you might want to consider is buy a very small affordable PWM controller and use it as an experimental toy to see if it works or not. If it does not work, you received an inexpensive lesson. If it works them buy a large one.


yeah at 20 bucks its worth a shot for the 10a one i found on ebay. I will report how well it works or if at all.


----------



## ken6881 (Oct 7, 2011)

What is the difference from deep cycle to regular lead acid batteries


----------



## MN Driver (Sep 29, 2009)

Regular lead-acid batteries, like the ones used in cars as starter have thin, sometimes porous/spongy positive grid plates. The thinner plates allow them to give more power in a smaller battery. Charging a lead-acid battery corrodes the positive grid plates, normally you don't really discharge a standard starting/lighting/ignition battery so this isn't as much of a problem and the typical requirement is to supply hundreds of amps for a short period of time and basically float charge or just sit there rest of the time.

Deep cycle batteries have thicker plates that can withstand the corrosion of charging and won't dissolve and crumble apart quickly after a small number of cycles. Usually 50% depth of discharge is still as far as you can go. With thicker plates there is less surface area so there will be more voltage drop but it is all a balancing act. Some of the thickest grid plates comes with batteries specifically designed for solar applications but these cells have plates thick enough to where the peukert and voltage drop is undesirable but they last a long time in a solar application but can't effectively push out the hundreds of amps that are needed in a car.

Usually golf cart deep cycle cells are a good combination of grid plate size and power capability. I'm not sure what the best lead-acid is to use today, seems no matter what you use the lifecycle will always be short unless you have very shallow and light amperage discharges to get them to last a long time.


----------



## Sunking (Aug 10, 2009)

MN Driver said:


> Usually golf cart deep cycle cells are a good combination of grid plate size and power capability. I'm not sure what the best lead-acid is to use today, seems no matter what you use the lifecycle will always be short unless you have very shallow and light amperage discharges to get them to last a long time.


Golf cart batteries are hybrid crosses between a cranking battery and deep cycle. There is also another marketing name for hybrid batteries called Marine batteries.

FLA Deep cycle on the surface seem like a good choice for EV's but in reality are not. Reason being FLA deep cycle batteries have thick heavy plates which makes the internal resistance too high for high discharge currents without excessive voltage drop and over heating. Deep cycles are best suited for long slow deep charges (no more than C/10) down to about 50% at max, then a slow C/10 to C/8 recharge. There is however one exception to the deep cycle batteries the AGM. AGM has fairly low internal resistance and can be discharged/recharged at C/4.

So for EV using FLA batteries the hybrid Golf Cart or Marine battery is the right choice.


----------



## piotrsko (Dec 9, 2007)

and based on the research I've done heavier for a given case size means more lead. marine batteries weigh about 45 lbs for group 31, my trojans SSC200 weigh 68lbs. the t1275's weigh 90 ea. guess which one has the highest 20 hr rating?


----------

