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Old 04-04-2013, 10:31 AM   #1 (permalink)
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Choosing a charger for 72V Lead Acid

Hi,
I'm trying to choose the right charger for my lead acid battery pack. I'm using flooded lead acid batteries. What I know so far is that the charger needs float charge capability to prevent overcharging, and I can use a 72v charger or multiple smaller chargers. I would like to use an on board charger so that I can plug in anywhere. Will these chargers charge to the correct cell voltage? What is the correct 100% and 0% cell voltage for flooded lead acid batteries? I've tried looking it up but have found answers anywhere from 2.1-2.5 for full.

My battery pack is 12 6v flooded lead acid golf cart batteries.

One option I was thinking of is using two of these chargers in parallel Alloy Shell 900W LiFePo4/Li-Ion/Lead Acid Battery EV Charger - BMSBATTERY
A standard 120V 15A outlet should handle both chargers. If one of them fails while I'm out someplace I can still use the other as a backup. I could mount a power strip inside my car, mount both chargers to a heat sink with room for airflow, and run the cable to the gas cap. This should let me plug in with an extension cord and use both chargers with a standard outlet.

This is another option I was thinking of. Schumacher SE-1072 Multi-Battery Charger

Is it best to leave my battery pack plugged in when not in use? Should I add a desulfator to help keep sulfation at bay?

If you have any suggestions about what charging set ups would work best for me please let me know.

Thank you,

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Old 04-04-2013, 03:18 PM   #2 (permalink)
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Individual chargers is a better option. It takes care of any balancing issues your pack might have (on the charging side at least).

You do not want to use battery chargers in parallel. No matter what, one will always put out a slighly higher voltage than the other and that just causes problems.

If you are buying a charger, get one designed (or programmed) for flooded lead acid, not lithium, and not even AGM or gel. The charge profiles are similar but voltages are different and it will cause issues.

Desulfators are not necessary unless you leave your batteries discharged for extended periods of time.

If you go for a single high voltage charger, the elcons are the cheapest I've found that I'd actually want to put in a car. The schumacher chargers work decent, but are horribly inefficient in my experience. If I had your setup I'd check ebay for some cheap ~10A chargers made for lead acid batteries.
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Old 04-04-2013, 11:53 PM   #3 (permalink)
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I have an Elcon charger in my car and it's great! when I bought it they called me up and wanted to know everything down to the brand of battery that I had so they could program it.
It's one of the few solid state chargers that I found that I could afford, because it's solid state it produces less heat, it's also less reliant on line voltage so it can handle 85v up to 265v AC input voltage and with the higher voltage it charges faster.
It's also weather tight with it's own heat sink, my old charger was not weather tight and burned up after driving in a heavy rain.

I would rather have a battery gauge that tells me a cell is out of balance then a charger for each battery in the pack.
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Old 04-05-2013, 01:40 AM   #4 (permalink)
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Thanks for the great suggestions. Individual chargers may be a problem because I am using 6v batteries. Most chargers I've found are 12v. I could use 6 12v chargers though. The Elcon chargers look good, but they also look expensive. I'm trying to keep this conversion low cost because the vehicle is not the best. I was thinking I could use one of these power supplies New 360W DC 12V 30A Regulated Switching Power Supply Universal Restaurant | eBay
Hot 240W 12V 20A Regulated Switching Power Supply Universal Minch for 5050 LED | eBay along with a charge controller like this 30A Solar Charge Controller Regulator 12V 24V Battery Charging PWM Solar Panel | eBay in order to make some low cost battery chargers. An Elcon charger would be about $0.45 per watt, if I could get these chargers to work they would be about $0.11/W. What are your thoughts on doing that?

Thanks for the great idea Ryland. I have a voltmeter for my full pack, but could easily run some wires to these little meters to monitor each battery individually. If one gets too low or high then I can attend to it specifically. 4 5 30V Mini LED DC Digital Voltmeter Display Wattmeter for Auto Car TRUCKLS4G | eBay
I do like the idea of being able to plug into 120 or 240AC. Some of these power supplies, like this one 12V 20A DC Universal Regulated Switching Power Supply | eBay , say that they can take 100-240V AC at 50-60Hz. I don't think that this is a necessary feature for me though as I will mostly just have access to standard 120V outlets.

An idea that I had that may be possible is to hook up one of these solar panels http://www.sunelec.com/x-specs/SUN/SunSP.jpg to my charge controllers. The problem is that the panel puts out 36.5V open circuit and 29V with a load in direct sun. This could possibly charge 1/3 of my battery pack, but I don't have room for three panels. I could definitely fit one, but I would have to be able to convert the voltage. If I make my own chargers with power supplies and charge controllers, I might be able to use the same charge controllers to charge the battery pack from the solar panel. If anybody has any more thoughts on how to make that work they would be greatly appreciated. These panels are Unframed grade B panels selling for $92.40, $0.42/W. Using these panels and a charge controller could be similar in price to a traditional charger if the voltage conversion is not too expensive. The Yugo does not have much roof space though so I could get a maximum of one 220W panel. According to PV watts http://rredc.nrel.gov/solar/calculat.../pvwattsv1.cgi a flat panel at my latitude will get an average of 4.6 sun hours a day, which would be just over 1kwh. Depending on the efficiency of my vehicle that could be 3-5 miles a day which would supplement between 20%-100% of my driving depending upon how much I drive. Even if that works I would still want to be able to charge from a wall socket, but perhaps I wouldn't need as large of a charger.

Please let me know if you have any more ideas or suggestions. Your thoughts are greatly appreciated.
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Old 04-05-2013, 10:24 AM   #5 (permalink)
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Midnight Solar is the only 72v charge controller that I found, they are also over $600... Xantex makes some nice 36v and 48v charge controllers that can handle high open voltages (over 100v open voltage) but splitting the power to two different charge controllers is sketchy with a good chance of equipment being destroyed.

How many sun hours would your panels get if you put them on the roof of your house? as much as I like the idea of charging your car off solar, you do need a way to fully charge the batteries right away or you will drastically shorten your battery life and with $1,500 worth of lead acid batteries I'm sure that replacing them is not high on your list.

There are not many options on Ebay for 72v chargers either without spending nearly as much as you would on a brand new one, the upside to that is that buying a quality charger isn't going to be much of a loss if you decide that you need to sell it, I tried to cobble together different chargers for a while, but I must say, I charger that just works and functions how the batteries want is great!
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Old 04-05-2013, 03:16 PM   #6 (permalink)
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Thanks for the reply. I agree, splitting the power could potentially be problematic. The cheapest I've found a 72v charge controller is $270, which would be about triple the cost of the panel itself. If the panels were mounted at the optimal angle due south on my house they would receive 5.05 sun hours, a little less than 10% more. The problem with mounting them on my house is that they're frameless non UL certified panels. I'd have to buy a frame to mount them along with fasteners and racking to attach them to my roof. I couldn't use them in a grid tie system because they're not UL certified, only an off grid system. To use them for my house I'd have to at a minimum buy an inverter, which will cost another $0.20/W and lose 5-10% of the energy. If I wanted to power my car off of this energy I'd have to invert it again through a charger, which would lose another 10% or so. All in all, mounting it on my roof would cost at least double what mounting on my car would cost and with system losses it would produce about 80%-95% of the energy that mounting them flat on the car without an inverter would. For most instances I think placing them on your house is the best route to go, but sometimes it might be better to put them where you want to use the power. Like you said, splitting the power to different charge controllers could be very problematic, so unless I can solve that I don't think I'll be able to implement a system like this. One possible solution might be to use a single 24V charge controller and charge three groups of 4 batteries each in parallel. Implementing the wiring could get very complex and possibly problematic though. I'm not sure if charging three 24v strings in parallel would interfere with my 72v wiring or not.

I might just bite the bullet and get a new charger. I'd have to spend more on the charger than my motor and controller combined though, but I don't want to ruin my batteries with a charger that is substandard.
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Old 04-05-2013, 10:07 PM   #7 (permalink)
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For a quick and dirty manual charger that can last until you get through the testing phase you could get a varrac with a volt meter and watch the amps with an amp meter.
You could also use it as a backup incase your main automatic charger quits.
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Old 04-06-2013, 12:23 AM   #8 (permalink)
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You could do six 12V chargers - two 6V batteries per charger.
I use six BMSBattery.com chargers - the 240W allow shell ones. I am very impressed by them - they pump out 10A right till cutoff at 14.8V, where they hold for about 15 minutes before switching to a 13.8V float.
Here are the details in my build thread when I first got them:
http://ecomodder.com/forum/showthrea...tml#post350615

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