Battery charging question

Steven Lake

Ok, battery charging question, charge controller aside. This is more for my curiosity and general knowledge as I'm fiddling with that mechanical charge controller again and I'm trying to figure out appropriate charge rates in order to adjust the unit for best performance. (IE, adding or removing windings to get the desired effect) And yes, it's another one of those "I've got nothing better to do so I may as well learn something" projects.

Alright, anyways, I've done some digging and came up with this formula for battery charging. (Note: The suggestion states that this is "best practice" but not the law of the land or anything like that, just FYI)

1. Bulk charge flooded batteries at the C20/5 rate. (IE, one fifth of the total capacity of the battery in amp-hours at the 20-hour rate).
2. Charge AGMs at the much faster C20/2 rate. (ie, up to 50% of the 20 hour rate)
3. Gel cells must be charged at less than C20/5. Preferably C20/6 and below.

Now, given this information, my question would be, is this correct? Or should my charge rates be different for each of these battery types? The rates sound right based on what I've read on the sides of different batteries I've encountered (such as the 2amp max charge rate on my 9ah AGM's) but I figured a second and possibly third opinion wouldn't hurt. My idea here is to have a rule of thumb I can use when actual OEM suggested charge rates aren't available for me to reference. Thanks guys. You're always hugely helpful to me.

Cariboocoot

Re: Battery charging question

Thing is the best charge rate depends on the particular battery. When you use generalized numbers they work, but are not necessarily perfect.
For instance a flooded cell can, as a rule, take C/10 (10%) without any problem and C/20 (5%) usually is too low in a "working system" but C/5 (20%) may be too high for some if not most.
And whereas some AGM's may indeed be able to take C/2 (50%) (some claim some rather magnificent rates in fact) not all would be happy with that so you're better off keeping it below C/5 (20%).
Gel cells are usually the most picky of all, yet recently we've seen an example of some which had factory specs for quite 'ordinary' rates.

Nothing like not having an answer, eh?

Steven Lake

Re: Battery charging question

lol! Yeah, and quite the answer. But overall I was just looking for a basic rule of thumb for those times when I *don't* have a max charging spec on the side of the battery. But from what you've stated there doesn't appear to be a really good rule of thumb to fall back on. Although, 10-20% capacity does seem to be the general "safe" rule for AGM and Flooded batteries. Gel Cell though seems to be somewhat of a crapshoot for what's best. o_0;; Thankfully I don't have anything that uses Gel Cell at this time. Although, given its popularity in certain things that may be inevitable, thus why I included that in my question just in case I happen across one in the future.

Cariboocoot

Re: Battery charging question

So make it adjustable! A couple of current-loading resistors ought to do it. A couple of switches and you get a variety of currents that can trigger the relays.

niel

Re: Battery charging question

i would not create a rule of thumb for charging different battery types as it varies too much by manufacturer. there is an agm out there that cautions against 30% and is a major brand.

westbranch

Re: Battery charging question

here is a very good article about what I think you want to know... I'm still digesting it all.

http://www.cdtechno.com/pdf/ref/41_2128_1199.pdf

Steven Lake

Re: Battery charging question

Huh, well, that's a start. It'll definitely help in the lead acid area. Now to find one for AGM. :P

westbranch

Re: Battery charging question

VRLA ( Valve Regulated lead acid ) = AGM

niel

Re: Battery charging question

westbranch wrote: »

VRLA ( Valve Regulated lead acid ) = AGM

actually gels come under the vrla heading too.