Charging MK Gel wont leaving bulk stage.

[Qvickster]

I have some MK Gels in Quantum Edge 2.0. They were installed in October 2018. When I try to charge them the light will not leave bulk charge state meaning the light stays orange even after 10 hours. I have the 8amp generic charger it come with by the way. I defiantly want to upgrade to the pl8 eventually. I hooked a multimeter to see voltage and its at 25.8 right after the 10 hours charge. Batteries only last about 2.5 miles. Basically my question is the batteries are bad or not? I have no idea how long people get out of them. It doesn't seem like the batteries are charging the last 20 percent or so. Btw I tried two different chargers. Both acted the same. Sometimes I wake up and the charger is blinking red after about 12 hours. I am getting new batteries anyway, but just wanted to see what anybody thinks.

Thanks,
Cody

I am also getting a XLR extension and shunt so I can see what the charger is putting out. Just for learning purposes.

[Burgerman]

I suspect that they are totally shot.

If you only charge that chair once a day, then the battery gets hammeded by overly deep discharges because its not big enough for the job.
An MK gel, charged properly (and your chargers dont do that) will give you at best 500 cycles to 80% depth of discharge before the battery capacity falls to 80 percent of new. And in a chair with too small batteries that means that you will be giving them the perfect storm.

Its like this. You get a few thousand cycles down to say 50% depth of discharge. Which would be the case if you had bigger 74Ah MKs fitted.
But you are likely discharging them to almost fully depleted daily. And when you do that (your 2 miles) to these already "smaller" batteries you will get at best 100 to 200 cycles. Thats around 1/3rd to 2/3rds of a year before they should have been replaced.

Batteries also die fast when the charger is charging at the wrong CV voltage. MKs lose around 50% of their service life if charged just 0.4V too high, above the correct 13.8 to 14.1 volt point.

Batteries die also from UNDERCHARGING. They sulfate if not FULLY 101% charged. That means approx 6 hours at CC stage, and another 8 to 14 hours at CV depending on discharge level and age. Takes around 20 hours total.

[Qvickster]

That's what I was thinking too. Once I get my tax refund back I will invest in a PL6. Make sure I give this new set of batteries their best chance at life. Can you give me a recommendation for a decent budget power supply.

[Qvickster]

I am also looking at a Victron 24v 8amp charger. Have you had any experience with those chargers. Can you set custom charge setting like the pl6.

[rover220]

I am also looking at a Victron 24v 8amp charger. Have you had any experience with those chargers. Can you set custom charge setting like the pl6.

yes, i am a fan of the victron. can create your own charge profile. not as in depth as pl8 but more than sufficient.

[Qvickster]

What exact model do you have?

[rover220]

What exact model do you have?

Use the 25v 8a, you'll need to solder an xlr.

[Qvickster]

I just purchased a DC bench power supply. From what I understand I can set the Max Voltage to 28.2 and max out the amps. My question is when do I go to a float stage voltage?

So once the batteries reach 28.2 Volt the current or amps to the batteries will start to decrease. How would I know when to stop it and not overcharge it?

[Burgerman]

You can safely continue charge at CV - when it reaches the 14.1 (28.2 volts in series) for 8 hours. Or until current falls to a tiny 1000th of capacity. So on a 50Ah battery thats 50mA. Although a chair thats OFF takes a few mA too. So add 20 to 30mA. So its fully charged when current falls to around 70 to 100mA. At that point no FLOAT is needed.

After 8 hours at CV, you can just reduce volts to a float voltage on 13.6 (27.2V) and leave it for a full day periodically on top of this to prolong battery life. But as long as its seen 8 hours to 12h CV at the correct safe voltage it isnt required.

Also, be aware that these are the max voltages at 20C. As temp increases, you should reduce these voltages a little.

Note. These are ODYSSEY batteries so are charging here at 14.7V in parallel with the PL8 so you can see the current fall over time. It started at 30A. If you continue the CV voltage, you can see that the current keeps on falling here. When it has been at CV for 8 hours on a deeply discharged battery it is still just about falling. But extremely low current. At this point its charged and needs no float. Gel batteries take longer.

Note that FLOAT is not needed to finish charge as long as you give the batteries 8 hours at CV (absorption) or until current falls to a really low level. Andstops falling pretty much. So you can charge from any big adjustable power supply. Use a decent voltmeter to set volts though.

[Burgerman]

Heres a volt and amp graph from a 24V Gel battery. Note how long it takes... Charging at 12A max via an XLR. At 28.2V

It needs another few hours to full as its still charging at 295mA (almost 1/3rd of an amp) and its still falling over time on that graph. So not done yet. After 8 hours at CV you should then drop to a lower float voltage in this case. Spending more than 8 to 12h at CV voltage can be harmful. Fortunately in most cases thats adequate for a complete charge.

Remember that if just adding some power back during the day, non of this matters. At say 30A charge on a power supply for 1 hour, you will put back a huge chunk of power for the rest of the day. Without running the battery low which does the real damage.

[Burgerman]

Volts V temperature.

CORRECT charge voltages for MK gel.

Damage caused to gel battery with a tiny overvoltage.
Realise that most mobility chargers charge at 14.4 to 14.6V for AGM batteries!

[Qvickster]

Thank you so much man. You are a huge help! I am going to try to give these new batteries the best chance they got. I going to start getting parts for a LifePo4 build here soon. Just so tired of the limited range I get out of the Leads. Thanks again everyone.

[Arima]

I am also looking at a Victron 24v 8amp charger. Have you had any experience with those chargers. Can you set custom charge setting like the pl6.

yes, i am a fan of the victron. can create your own charge profile. not as in depth as pl8 but more than sufficient.

That looks like a nice little charger/power supply. Graphing and history also.