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Old 04-15-2012, 08:47 PM
sentraelectric sentraelectric is offline
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Question Chargin practices for lead acid batteries.

Hello.

I built an electric car with lead acid batteries (waiting for LIFEPO4 batteries to become more affordable for me) and I'd like to ask a few question to the community about how to make them last longer.

The battery pack is a nominal 120V system and I am using 20 6V Deka GC25 batteries which are 235ah. I charge them with an Elcon PFC 3000 (5 stages S1=127V, S2=142V, S3=144V, S4=148V and S5=133.5V) at 240V (about 13 amps). It can also charge at 110V (about 18 amps).

I get a range of about 50 miles per charge on ideal conditions at about 50mph, and about 40 miles in traffic, some highway, etc.

Questions (I need answers to make the batteries last longer) :
1. Is it better for the batteries to charge at 110V or 220V (slower or faster charge)?
2. I get up to 1,000 amps from the controller when I accelerate for brief periods. Does this seem excesive for these batteries (cruise at 50mph uses about 250 amps)?
2. I work close to home, so I can charge for a short while I come home for lunch. Is this good, or I should avoid partial charges and only plug in when I can do a full charge.?
3. When fully charged, my voltage is 135V. I marked my discharge level at 110V, but I have actually discharged them max to 115V. Does this seem OK or I am exceeding the safe lower limit? I understand that overdischarging them is what kills them faster.
5. After the pack is fully charged, should I unplugg the power, or just leave the charger connected? When it is fully charged, I can still hear a little of the "boiling watter" sound comming from the batteries, so, I know the charger still applying some power to them, but I don't know if this is good or bad for the batteries.

Thank you. I appreciate the help.

Jose.
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  #2  
Old 04-15-2012, 11:18 PM
gottdi
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Default Re: Chargin practices for lead acid batteries.

Full Static Open Resting Voltage should be right around 127.4 volts or 6.37 volts per cell at 100% charged. At 115 volts or 5.75 volts per cell you would be sitting at around 10% ideal conditions. Charging at 240 or 110 does not matter but 240 will do it faster. Once you charge and let it sit for 12 hours you should be normally at 6.37 volts per cell static resting voltage. Right off the charger you might be seeing 135 but much of that is what is termed as surface charge and it blow off instantly once you apply power. It really does not give you much in the way of usable AH's from your batteries. Take care of them and check your specific gravity once and awhile and keep the water at the proper level and only use distilled water. Keep the tops clean and try not to discharge them to 10% very often. If you are really getting 50 miles at 50 mph you must have some very special lead batteries. Best I ever got was 25 miles and that was between 45 and 55 mph to the point that the car was just creeping along and the batteries were new and all held a charge just fine and never ever pulled more than 550 amps from the batteries. If your pulling 1K amps from your batteries you are asking a lot and I would not expect them to last much more than a couple to three years. That is pretty normal and the power and performance just get worse and worse as time moves forward.

You will love lithium cells. Guaranteed.

Pete
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Old 04-18-2012, 12:29 PM
sentraelectric sentraelectric is offline
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Default Re: Chargin practices for lead acid batteries.

Hello Pete.

Thank you very much for the information. All that you write makes perfect sense. I had no idea about the gravity test. I should look into that.

Yes, I actually get 40-50 miles per charge from these 20 6V - 235 ah.

I will try to take it easy on the acceleration to reduce the 1K amps and to try to make them last longer. I will be happy if they last 2 years or 15,000 miles at least. I am looking forward to upgrade to lithium, but I have to amortize the cost of the conversion for now, so when these lead acid go bad, I will be abel to upgrade.

Thank you for the voltages table and for all the tips. It is very useful.

The only thing I didn't see in your response is if I should leave the power cable connected after the charge is complete or I should disconnect the charger. The charger maintains a steady voltage after it has completed the charging cycle and I am wondering if that is good or bad. The charger manual does not say anything about it. My guess is that it is good or otherwise, the charger would shut down itself, but I want to be sure.

Thank you again Pete.

Jose.
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Old 04-18-2012, 02:05 PM
gottdi
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Default Re: Chargin practices for lead acid batteries.

Leaving it connected is fine. It will remain in what is called a float charge. You don't want a float charge for lithium. Lead acid are fine to leave on float as the voltage is lower than the ending charge voltages and any power that is taken into the batteries is next to nothing. It just keeps the batteries from draining if you leave them and don't use them for a long time. It maintains the voltage level as lead acid batteries WILL discharge on their own unlike the LiFePO4 lithium cells which will hold a charge for a very very very very long time if not used unless you have parasitic loads on your vehicle that need power then they will drain down.

Pete
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Old 04-19-2012, 06:52 AM
sentraelectric sentraelectric is offline
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Default Re: Chargin practices for lead acid batteries.

Hello Pete.

Thank you for your reply. You know a lot about batteries! I appreciate the help. I think I have now what I need to know to take better care of my batteries.

Thank you again for sharing the knowledge.

Jose
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Old 04-19-2012, 10:15 PM
coulombKid coulombKid is offline
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Default Re: Chargin practices for lead acid batteries.

I've got a Harbor Freight float charger for the truck I only drive occasionally. At 75 degrees F I'm reading 12.56 volts at the float charger outputs. Is this really enough to save the starting battery from auto discharge? Are their any float chargers (affordable) with a temperature sensor, a look-up table in a microprocessor and an A/D converter to check the controlled output voltage? Here in Phoenix cheap lead acid batteries get killed quicker because of summer heat. With Delco Golds I've made 95% of prorated warranty life and with the older Optima red tops I've exceeded that mark by a fair margin.
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Old 04-19-2012, 10:43 PM
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Default Re: Chargin practices for lead acid batteries.

Are you reading that while connected to a battery or not? It should float a fully charged battery much higher than that. I have 3 HF chargers (2 models) and all of them float just fine.
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Old 04-20-2012, 10:15 AM
coulombKid coulombKid is offline
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Default Re: Chargin practices for lead acid batteries.

Quote:
Originally Posted by Ziggythewiz View Post
Are you reading that while connected to a battery or not? It should float a fully charged battery much higher than that. I have 3 HF chargers (2 models) and all of them float just fine.
I suspected this one is too low. I had heard that they should float at 13.2 volts. I read it with the clips off the battery because it would take a while after use for the voltage to drop to that.
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Old 04-20-2012, 10:59 AM
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Default Re: Chargin practices for lead acid batteries.

If the clips are off the battery you won't see the real charge ability. If I put a charger on a dead battery it might read 10V, does that mean that is the charger's limit? No, it means the battery is under 10 and the charger will raise the voltage as necessary to keep charging the battery until full.

Same as an alternator, if you want to check if your charger works, test a less than full battery before and after hooking up the charger. The voltage read should go up when the charger is connected.
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