Charging GEL Deep Cycle with Ctek Controller at 14.4V (1 Viewer)

[MioExped]

I got an ARB fridge (50qt) and a deal on a 200Ah Renogy GEL battery with Ctek D250SA charge controller. I have a 100 W solar panel inbound (Rockpals).

Renogy 200Ah GEL battery

The issue came then that the Renogy GEL battery wants a charge voltage of 14.2 per the manufacturer. The Ctek charger controller has some awesome features (manages alternator or solar inputs, isolates crank and aux battery, 20A charging feed, selectable wet cell/AGM, etc.). However, it lists its output voltages as 14.4V or 14.7 volts depending on if wet cell or AGM batteries are used (selectable).

So, what will happen if I charge the Renogy GEL battery on the closest setting it allows, the 14.4 V? I emailed both Ctek and Renogy and got somewhat incomplete answers. Renogy says "yes you can, but be advised that you may reduce the life of the battery". But by how much?

I don't want to kill this beast of a battery, but I also don't want to have to buy a different charge controller. What would the long term effects of charging it on 14.4V instead of 14.2V?

Any input would be appreciated.

 

[e9999]

I've done plenty of unadvisable experiments pushing the envelope myself, but TBH I would not recommend to somebody else to use 14.4 if the manuf tells you not to. (Even though that 14.2 seems odd to me, maybe a CYA thing?) Simply because it is true that you can damage some batteries by overcharging, and you may never know how safe this would be for your particular one. Assuming there is no way to adjust your current controller more precisely, I'd compare the cost of another battery vs the cost of another controller (minus any resale value) and then decide which way to go.

I would also suggest you try again with Renogy, call and try to talk to an actual tech or engineer, be friendly with him or her on the phone, and ask something like "I know the official position of the company is that... but in real life what.... etc". You are more likely to get an honest opinion than in email.

 

[MioExped]

I've done plenty of unadvisable experiments pushing the envelope myself, but TBH I would not recommend to somebody else to use 14.4 if the manuf tells you not to. (Even though that 14.2 seems odd to me, maybe a CYA thing?) Simply because it is true that you can damage some batteries by overcharging, and you may never know how safe this would be for your particular one. Assuming there is no way to adjust your current controller more precisely, I'd compare the cost of another battery vs the cost of another controller (minus any resale value) and then decide which way to go.

Renogy said: " Yes, sure you can (charge at 14.4V instead of 14.2V). However, please be aware that we are not charging the GEL batteries at the correct voltage. This may or may not cause the battery's lifespan to shorten. "

So how much shorter lifespan? 3%, 15%, 45%?

I got a great deal on it, so I'll probably keep a data log on it, run it with the current sub-optimal system, and watch for performance loss. If I get "x" trips out of it, I will be happy. Then iterate again for the next system.

 

[e9999]

I don't think you will ever get a precise answer as to how much that alleged reduction will be, so you're on your own probably. I am surprised they would say 14.2V especially since I always thought that AGMs need more voltage for full charge than FLAs, not less, so that seems like a CYA lawyerly statement to me. And the obfuscating nature of the response would make me disregard it even more. If you don't want to get something else, well then do the 14.4 and you'll probably be fine. Could lose some life expectancy maybe (unlikely?) but I doubt that the battery will explode at 14.4 . It's not like it's a cobalt-lithium battery ticking fire bomb. So, basically, meh...

 

[MioExped]

I don't think you will ever get a precise answer as to how much that alleged reduction will be, so you're on your own probably. I am surprised they would say 14.2V especially since I always thought that AGMs need more voltage for full charge than FLAs, not less, so that seems like a CYA lawyerly statement to me. And the obfuscating nature of the response would make me disregard it even more. If you don't want to get something else, well then do the 14.4 and you'll probably be fine. Could lose some life expectancy maybe (unlikely?) but I doubt that the battery will explode at 14.4 . It's not like it's a cobalt-lithium battery ticking fire bomb. So, basically, meh...

Agreed. Note this is a GEL, not AGM. From my research yes, the AGMs take more voltage, and the GELs seem to be more manufacturer specific.

Nothing I see either says this is a safety risk though... I don't think you can blow up a battery by going 0.2 V over the stated charge!

 

[e9999]

My mistake, I incorrectly understood "gel" as in a generic term for "AGM". Yes, actual GEL batteries do indeed seem to need a lower absorption voltage. So, forget what I wrote last, I don't know enough about those, sorry.

 

[spressomon]

No direct experience with gel type batteries here but here's the page from my Sterling DC-2-DC 1260 charger FWIW.

 

[spressomon]

Holey zoom out! Oh well, better than having to get out the magnifying glass

 

[Suprasoup]

Long term you’ll wreck the battery charging at 14.4v or higher. The gassing voltage of a 12v lead acid battery is 14.4v (temperature dependent). Gel batteries have a limited ability to deal with gassing due to the gel like nature of the acid that gives it its name. Gas bubbles tend to get stuck in the gel. The voids created represent areas that are no longer chemically active aka permanent capacity loss. The more the battery gasses the more capacity you lose. It’s the reason why gel battery charge voltages are lower than other lead acid batteries. Gassing is also the reason why gel batteries are current limited as well. Too high a charge current and gas bubbles form as well.

A few options to drop the voltage. Adding a diode. That’ll drop voltage a bit depending on what type of diode you use. Another option would to be to add a bit of resistance to the charging wires going from the ctek to your battery.
Using a slightly thinner wire or making the wires physically longer would both work. Look up voltage drop calculators online to guide you on recommended wire length.

All that said that’s a big honking battery with a small solar panel. You might never get to the absorb voltage using just solar. I’d measure the voltage at the battery terminals while charging to see what voltage actually gets to the battery.

 

[PeterTheBeater]

Ive read quickly thru the renology bat and the ctek datasheet, it really shouldn't be charging at 14.4V, that's pretty high imo. I think realistically it would be around high 13's. You shouldn't really drain your battery past like 60% and according to Ctek they only ram 14v when the battery is up to 80% charged. IMO, 0.2V difference isn't going to do anything really noticeable as it's going to charge it at that voltage only when its very low and for short periods of time. You will get some voltage drop in your wiring anyway.