Constant current battery chargers

Salvo wrote:
What do you mean by SAFELY? No explosions? That charge rate will definitely boil your batteries. Probably need to fill water every week.

The 20C of your typical 220AH battery bank is 11A. 8% of 11A is 0.88A. Maintaining 14.8V till current drops to 0.88A is no way to treat your batteries. Sounds more like a equalize procedure.

Sal

MEXICOWANDERER wrote:
At 20C the "fastest" way to SAFELY recharge FLA batteries is to apply 14.8 volts until such time as the current drops to less than 08% of total 20 ampere hour rating.

Sal, you actually need to DO this stuff rather than merely pontificate over it.

The formula worked for what, thousands perhaps tens of thousands of battery charge cycles.

At 68F try it sometime, apply 14.8 volts and disconnect from charge at 8.5 amperes for a standard 105 ampere hour BCI group 27 battery.

REMEMBER! This is to minimize generator run time, and is NOT APPROPRIATE for shore power recharging where a generator is not gulping fuel at several dollars an hour. I furnished that formula.

And no, you cannot drive to Death Valley Scotty's castle, in August, or Prudhoe Bay in February and do this either. That's why I furnished a Celsius temperature rating for this.

Left at 14.8 for a long length of time, a battery will indeed electrolyze too much water. The 8% amp hour limitation should have provided enough of a clue to keep you out of trouble.

Fuel costs money. So do worn out generators, runs to the gas station, oil changes, and baseball size rocks chucked through the living room window because you run the generator too long. So what if an off grid battery trades 5% of it's total possible lifespan to save oh say four or five hundred dollars? It's helps to live completely off grid for several years or be an engineer to appreciate this point...

That makes sense; down to 18A. Still, something is missing. What's the constant current charging rate?

Sal

I take it to mean 8% of 220.

What do you mean by SAFELY? No explosions? That charge rate will definitely boil your batteries. Probably need to fill water every week.

The 20C of your typical 220AH battery bank is 11A. 8% of 11A is 0.88A. Maintaining 14.8V till current drops to 0.88A is no way to treat your batteries. Sounds more like a equalize procedure.

Sal

MEXICOWANDERER wrote:
At 20C the "fastest" way to SAFELY recharge FLA batteries is to apply 14.8 volts until such time as the current drops to less than 08% of total 20 ampere hour rating.

AFAIK, the only converter that keeps its Vabs till the batteries are near full is the WFCO. But it is notorious for not being able to get it to start at 14.4 and it stays at 13.6. Some report theirs works ok.

The PD has the Charge Wizard, so you can make it do 14.4 and it should then hold that ok. This makes it a good choice as long as you accept the initial charging rate will be a bit less than the "size" of the converter. (An "80" will do 75, etc.) Over-all, a good compromise for various reasons.

The PowerMax is a really good converter, but it does drop to 13.6 for the absorption stage, so it would not be the fastest. The variable voltage model seems not to have been brought to market, but you must ask Randy at bestconverters about that. (Perhaps it can be special ordered)

Mr Wiz has the WFCO 68100 which should be great although it has 14.4 as Vabs instead of 14.6 like the PowerMax. But at least it stays at 14.4 instead of dropping to 13.6 "too soon".

Iota works well but also drops to 14.2 for the absorption stage.

I find the best results are with the Vector/BD portable chargers but the highest "size" is 40a. You can run several of them at once to get more amps though. They do not do Float, etc, so they cannot substitute for a converter when on shore power.

All the above has to be balanced against your charging intentions while on gen. The SOC the batteries are at when they reach Vabs depends on the charging rate you start out with.

If you start at a 30% rate, you will have the batts to 14.x at about 65% SOC. If you use a 10% rate they will take a long time, but get to 14.x at 90% SOC.

So if you are doing "50-90s" and your batts get to Vabs by 75% SOC at about 20% initial charging rate, then you will do the remaining 75-90 with amps tapering. That is still faster than starting at a lower rate and getting to a higher SOC before amps taper. People forget that little fact :)

You might choose to run 40-80s instead of 50-90s. Now you only spend the last 5% SOC with amps tapering. Much faster, and now your PowerMax drop to 13.6 doesn't matter so much because you don't go past that point on gen very far anyway.

So you have to juggle your priorities and set-up to suit yourself.

Another thing about fast charging is that going higher in starting amps charging rate has diminishing returns. You do not halve your time by doubling the amps. But you get more time reduction going from a 30amper to a 50amper than you do going from a 60amper to an 80amper.

You can spend a lot more money to get 15 minutes less gen time for a 50-90 if you aren't careful.

The gen itself is your limiting factor in many cases, where it takes a certain VA to run that many amps worth of charging. A PF corrected charger lets you do more amps with the same amount of gen VA.

All 3-stage converters are supposed to operate in constant current mode while in boost. Some converters, like the PD do not get into constant current mode due to a poor design. This means the PD will charge batteries slower.

If you're looking for a fast charge then you want a converter that can output rated current for more than just a few minutes. You want a converter that has a high max voltage when in boost. The Iota works very well because its max voltage is 14.8V. A converter that has a max voltage of 14.4V will exit constant current quicker and begin to taper current.

It's also important to have big fat cables from converter to batteries.

Sal

They're all about the same overall. But if you could get a higher voltage Paramode, IMO, it would be the fastest due to its higher voltage absorb phase. But you can't technically so either IOTA or PD or Powermax. I like Powermax cause you can get it with adjustable voltage (I think), it's 100A, and it runs from a 15A VAC circuit (cause it's PF corrected).

MEXICOWANDERER wrote:
At 20C the "fastest" way to SAFELY recharge FLA batteries is to apply 14.8 volts until such time as the current drops to less than 08% of total 20 ampere hour rating. Any other formula for 5% antimonial batteries is bogus science. If power runtime is not an issue, apply 10% of total ampere hour rating until such time as 14.4 volts is reached. For top charging apply 2% of ampere hour rating until such time as 15.0 volts is achieved.

Another golden piece of info from MEX!! Was that .08% or 8%??? Forgive my stupid question but do you put it into float at that point or perform the top charge portion?

I need a big amp, PF corrected, power supply to try all this out.

At 20C the "fastest" way to SAFELY recharge FLA batteries is to apply 14.8 volts until such time as the current drops to less than 08% of total 20 ampere hour rating. Any other formula for 5% antimonial batteries is bogus science. If power runtime is not an issue, apply 10% of total ampere hour rating until such time as 14.4 volts is reached. For top charging apply 2% of ampere hour rating until such time as 15.0 volts is achieved.

Thanks BFL. That is what I thought I knew, but wasn't so sure. :)

What's the thinking in 2013 as to the converter/charger which yields the shortest gen time? I'm only working with 2 cheap 27s, so I'm not that concerned with treating them with kid gloves. They'll die of age and idleness anyway. OTOH, I can't get to them to maintain them, either. LOL. I should spring for the watering manifold gizmo.

But anyway, given proper wiring, which converter as of now for shortest gen time (Onan microquiet non-inverter)?

The constant current charger would maintain the current past where the battery acceptance rate would normally start to taper that current (when the battery voltage reaches a certain point)

The "charging profile" of modern chargers is to have an initial stage (Bulk) with constant current with a current limited charger (different "sizes" of current available to choose from when buying a charger), then as the battery voltage reaches the chargers set-point for holding there for the absorption stage (Vabs) now the charger begins its stage two (Absorption) where the amps will taper. The tapering is from the battery voltage getting up closer and closer to the charger's voltage until they are the same (battery full)

So now the issue is what to pick for Vabs? Battery specs are different on that among brands and types of battery. Mostly the usual Vabs of around 14.4- 14.6 is good for AGMs or Wets. (but too high for Gels)

Note that the above profile and its "stages" has little to do with the so-called "three-stage converter" stages of 14.4,13.6 and 13.2 volts. In that case, the initial 14.4 stage is held while the battery voltage rises to 14.4 (you might get constant amps during this period, or a vaguely tapering sort of amps with a PD which can't seem to do constant amps like some others can) Now the difference is that instead of holding that 14.4 as Vabs while amps taper, some converters drop to their second stage for Absorption at some lower voltage. That makes for a longer gen time to recharge the batteries, but is considered to be more "gentle" where they can advertise it makes for a longer battery life. I'd rather have shorter gen time.