# My first 72V charge on my new AGMs isn't going well...



## mechman600 (Oct 16, 2010)

I was using individual 12V chargers.

I made up simple Lee Hart regulators with a 6.8V & 6.2V zener, so it starts shunting through the PR2 bulb at 13.0V. I tested all regulators and they are okay.

Today I installed my Kelly 7210 charger. It holds voltage at 88.2V. Everything stayed even until about 13.5V per battery. Now at the end of the charge two batteries are at 15.5V. Two are below 14.0V - these two were higher and then started dropping in the last while while others went too high (they are a slightly different battery than all the others).

Right now it is at 2.0 amps and not shutting off. This charger is not adjustable.

What is going on? More importantly, am I letting the smoke out of my nice new AGMs?


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## mechman600 (Oct 16, 2010)

Ok - it just shut off and went into float mode. Maybe my regulators will eventually even things out at this reduced voltage?

It doesn't make sense because I fully charged all batteries with my 12V charger before installing this setup.


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## Ziggythewiz (May 16, 2010)

Not sure what your regulators are supposed to do, or why you think you need them.

Your batteries are probably supposed to get to ~15V during the gassing cycle, at least according to my (QuickCharger) manual.

How does the manufacturer say to charge your batteries?


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## mechman600 (Oct 16, 2010)

The regulators start shunting current through a resistor above 13.0V. They are supposed to keep things balanced at the top.
Here's a link:
http://www.evdl.org/pages/hartregs.html

Max charging V for my batteries is 2.43VPC @ 25C (14.6V). No gassing cycle. It's about 10C out right now, so going a bit higher won't hurt (14.95V), but 15.5V is way too high.


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## frodus (Apr 12, 2008)

but you don't need shunt regulators if you're already individually charging the batteries.....

shunt regulators are for series charging.... i.e. a 72V charger.


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## mechman600 (Oct 16, 2010)

I WAS using individual chargers.

Today is the first time series charging with my new 72V charger.


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## frodus (Apr 12, 2008)

oops, read that wrong.... sorry.

What's the shunt current?


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## mechman600 (Oct 16, 2010)

Only a small amount. It's meant to keep slightly unbalanced batteries in check.

Taken from my link above and corrected for 6.2+6.8V zeners instead of 6.8+6.8V in the link:
1ma @ 13.25V
10ma @ 13.6V
100ma @ 13.9V
200mA @ 14.0V
500mA @ 15.0V
730mA @ 16.0V


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## DIYguy (Sep 18, 2008)

Ziggythewiz said:


> Your batteries are probably supposed to get to ~15V during the gassing cycle, at least according to my (QuickCharger) manual.
> How does the manufacturer say to charge your batteries?


You don't want AGM's (or gel's or any sealed pb battery) reaching a gassing cycle. 
Good advise about the manufacturers charge recommendations.


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## Ziggythewiz (May 16, 2010)

It's my understanding that AGMs are supposed to gas, just not as much as floodies.
I've heard from some places they do and some they don't though, so it must depend on the specific battery. 

I'm using an AGM charge profile to go easy on my floodies. It gasses, just not as vigorously.

If the manufacturer says to charge much above the full resting voltage (which 14.6V is) they have to gas.


@Mechman 
You said some batteries were a different type. Do they specify the same charge voltage as well?



Found this from Lee Hart addressing someone's similar concern:



> > Ben Apollonio wrote:
> > > Would someone please verify my understanding of AGM charging?
> > > While topping off my Deka 9A34 sample today... I thought the side
> > > of the case appeared to be bulging slightly.
> > ...


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## DIYguy (Sep 18, 2008)

Ziggythewiz said:


> It's my understanding that AGMs are supposed to gas, just not as much as floodies.
> I've heard from some places they do and some they don't though, so it must depend on the specific battery.
> 
> I'm using an AGM charge profile to go easy on my floodies. It gasses, just not as vigorously.
> ...


Well, if they gas a small amount, the electrolyte will recombine. If they gas enough to cause a pressure build up, then they vent and this is lost. The venting will destroy the battery over some cycles. So, they tend to have charge recommendations that stay away from much/any gassing. Balancing (other means) in a series string should be used for SLA's.


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## tomofreno (Mar 3, 2009)

From battery university:

"As with all gelled and sealed units, AGM batteries are sensitive to overcharging. These batteries can be charged to 2.40V/cell (and higher) without problem; however, the float charge should be reduced to between 2.25 and 2.30V/cell (summer temperatures may require lower voltages). Automotive charging systems for flooded lead acid often have a fixed float voltage setting of 14.40V (2.40V/cell), and a direct replacement with a sealed unit could spell trouble by exposing the battery to undue overcharge on a long drive."


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## mechman600 (Oct 16, 2010)

Thanks for that info. It's good stuff.

When charging, all battery voltages are quite even up to about 14.0V. That's when some start shooting up. So This charger will not work. Kelly says this charger is what it is and cannot be adjusted. I did specify flooded lead acid when I ordered the charger but I have since replaced my floodies with AGMs.

This will not work and I need to spend more money on a charger. I guess it will be easy to sell my old one because it will do lithium as well.


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## Ziggythewiz (May 16, 2010)

Assuming this charger is okay with pulling the plug, you could just set something up to cut the power to the charger when it gets where you want it.

Also, should have mentioned it was a floodie charger to begin with.


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## mechman600 (Oct 16, 2010)

I have pulled the plug a couple of times. The "power" and "charge" LEDs flash for a bit. It might be a bit angry, I don't know.
Coming up with an automatic way to unplug my charger is beyond me. I'm not great with electronics.
A D4840 relay signalled by a normally closed relay that's triggered by zener diodes off pack voltage? But that wouldn't latch to keep the charger off. Hmmm...I might have to rely on my 115VAC timer for now, but that's a pain.

(...a pause while the more electronically apt pipe up....)

I thought my mention of 88.2V cutoff was enough to imply that it was for floodies. Sorry.


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## Electric Forklift Guy (Dec 13, 2012)

What it sounds like is that you have is two batteries that have a different "internal resistance" than the others.

If this is the case then you wont have a problem charging them individually but once you try to charge them in series you'll get voltage imbalance

You can usually find the "internal resistance" on the data sheet on-line.
The problem can also occur with identical batteries of different ages.

Most AGM six cells finish at 14.4 - 14.7 Volts.

Since you're not real far off ,I'd try running the batteries down and re-charging with the 72 volt charger and see if they equalized on their own before you start tearing stuff apart.

During the recharge keep track of 

1. Voltage
2. Temperature , you're just checking to make sure none of the batteries are noticeably warmer
3. Excessive swelling.


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## mechman600 (Oct 16, 2010)

Thanks for the advise. I have discharged and charged multiple times (I commute with the eBooger every day), although no deep discharges, and charging is the same every time. What I am doing right now is using a timer that shuts off before voltages go way out of whack.

It seems that voltages are dead even until 14.2V. Only above that is where things go wonky. I have ordered another Kelly 7210 charger with a max voltage of 84.0V (14.0V/battery, 2.33VPC). My battery manufacturer recommends 2.30-2.43VPC for constant voltage charging. It will be interesting to see what happens with a charger that maintains 84.0V during absorption phase - whether everything will stay happy and even or still go wonky.
I will post results.


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## Ziggythewiz (May 16, 2010)

Guess if you're getting another charger you don't have to worry about it, but if you wanted to cut power via a relay a JLD404 or programmable voltmeter would make it really easy, or maybe your regulators could be adapted to trip the relay.


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## mechman600 (Oct 16, 2010)

Yeah, I figured that I'd better buy another charger to keep things simple and reliable. I figure I can sell my old charger for close to what I paid for it since it's basically brand new anyway.


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## mechman600 (Oct 16, 2010)

It gets worse. I got my new Kelly charger today, plugged it in, and....NOTHING.
There are two LEDs - one indicating power and the other indication charge. When the charge light changes from red to green, it's charged. My new charger's charge light is green...all the time. No matter what.
I tried driving around the block to get system voltage down a bit (to 74.2V), but nada. Nothing. Maybe I should go for a longer drive to get it down even more. I don't know.
I emailed Kelly but have not gotten a response back yet.


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## mechman600 (Oct 16, 2010)

Update. Kelly agreed to send me a new replacement. But I decided to just send it back for a refund instead. This is because I have two types of batteries in my pack with differing internal resistances. This [obviously] makes balancing them while charging nearly impossible. My Lee Hart regulators cannot even come close to this task.

My [hopefully] final solution is six chargers from BMSbattery.com - the 240W (12V/10A) ones. They shipped today, so I will hopefully see them in the next couple of weeks. Because of my mish-mash battery pack, I have concluded that individual chargers is the only real answer, at least to keep things simple.

I will update once I have the new ones installed, as well as measured efficiency numbers, etc.


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## mechman600 (Oct 16, 2010)

The new chargers are in!








Some testing revealed that they work exactly like I want them to. They bulk charge charges to 14.7-14.8V, absorption for about half an hour at this voltage, and then float at 13.6-13.7V. I measured them to be 75% efficient no matter what output current/voltage is at.

I tied pairs together as "charger stacks". One stack is behind each seat and the other stack is on my control board under the hood.
















And here is a picture of something that I have yet to do with any of my chargers so far:








Float charge.....something that every other EV owner takes for granted! I left them on float for about five hours to make sure the batteries were fully saturated and extra happy (for once).

Now it charges up in less than half the time of my Mastercraft chargers because the current does not slow down as the battery voltage and resistance rises. Finally! A charging solution that works!


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## Duxuk (Jul 11, 2009)

I started to get a bit panicky reading this and another thread about AGM charging. I have 5 Lucas LSLC22-12s which I charge with a 3 phase 48V nominal charger for 4 of the batteries and a CTEK 12V for the fifth. I was worried that 58V may be too much at the end of bulk and during absorption for the 4 batteries but was relieved to find that Lucas recommend 14.5-14.8V per battery, so I'm doing nothing wrong!
Balance of the 4 has remained good. I tried a 60V charger for the 5 when I first got them but found it had no absorbtion phase. At 72.5V it cut off. The result was dropping battery voltages and performance in use, right from the start, so I clearly wasn't fully charging. Range would have been lower too. I have put about 130 charges of, usually, about 50% DOD on them and range and performance seem much as when I began in July 2012. I have run them completely flat once with no apparent damage. 
All hail to LUCAS-The Prince of Darkness.


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## Electric Forklift Guy (Dec 13, 2012)

mechman600 said:


> Update. Kelly agreed to send me a new replacement. But I decided to just send it back for a refund instead. This is because I have two types of batteries in my pack with differing internal resistances. This [obviously] makes balancing them while charging nearly impossible. My Lee Hart regulators cannot even come close to this task.
> 
> My [hopefully] final solution is six chargers from BMSbattery.com - the 240W (12V/10A) ones. They shipped today, so I will hopefully see them in the next couple of weeks. Because of my mish-mash battery pack, I have concluded that individual chargers is the only real answer, at least to keep things simple.
> 
> ...



A lone figure races through the woods late in the night

clutching his bundle to his chest he ignores the branches that tear at his robes...he must reach the altar before the witching hour has passed

He reaches a clearing , unsure if this is the right one

Has he lost his way? a desperate panic begins to build until the clouds pass from the moon and the ancient altar of In'Ja Near Ing is revealed just a few feet ahead of him

He quickly unfurls his bundle and begins his preparations

He anoints his hands with oil of "double yew de forte" then binds them with tape of duck

Chanting the mantra "Git er dun" over and over he lights the fire

The ancient coals of burnt transistors burst into flames , he reaches around gathering up the damp leaves of the clearing and tosses them upon the fire.

"Oh great god Murphy " he cries " I offer you smoke ...take this offering of smoke given freely and do not steal the smoke from my chargers !"

Then silent minutes tick by and the man waits ,finally a groan comes from the altar.

"Your offering is accepted mortal" the man is noticeable relieved " I will spare your chargers and your batteries,but I require one more sacrifice"

"What my Lord?" the man asks.....but he already knows the answer , it is the sacrifice all followers of In'Ja Near Ing must make.

"You must never lay with a woman".

"As always" the man replies.


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