Amps Size for Finishing Stage Charger

I "recommend" the dunce that wrote that recommendation and his clone supervisor who approved it both are eligible to get a frontal lobotomy.

It isn't that the information is not correct. It is. For one single solitary type of usage. That which is the easiest on the battery and makes the manufacturer look as good as it possibly can.

There is a growing market segment that does not live in battery manufacturer dreamland.

The market segment relies on burning hydrocarbons to recharge. It is economically foolish and ecologically stupid to recommend excessive generator run time just to make their product have perfect lipstick.

Manufacturers are NOT DOING THEIR JOB. Period. They can if they wish amplify and extend recommendations for those customers who wish to read and learn. How much trouble and expense would it take to provide extended information? Plug N Play'ers buy a battery and toss everything except the warranty into a trash bin.

What is the recommended maximum permitted charging (bulk) amperage at 80F, a not unreasonable assumption for vacation weather.

What is the recommended maximum permitted absorbsion voltage limit at 80F?

What is the recommended float voltage limit at 0F? 30F? 60F? 80F? 100F?

Is it stressful to declare the above information is valid only when using a temporary charging source like a petroleum fired generator? Sure it is. Someone has to actually -think- and consult with overly timid engineers and somehow force them to untoe the company line.

This is EXACTLY why I never sought employment in a regimented environment. I had a sign alongside my front door

SALESMEN ARE NEITHER SOLICITED OR APPRECIATED. ENTER AT YOUR OWN RISK.

Visiting customers used to howl with delight. Inside....

THIS IS NOT BURGER KING. YOU DO NOT GET IT YOUR OWN WAY.

smkettner wrote:


If it is a top charge I would think you would hold the 14.4 to 98% to 100% then do a top charge. 6 to 10 amps would be plenty IMO for your 4 batteries. Better to give these batteries a bit more time IMO.

Yes for sure. I was confused about just when they wanted to cut in the 15.x charger but one was for those with PowerMax or Iota converters once they finish the Bulk stage. That would be earlier than 90% SOC with a decent charging rate though, so the finish charger could do with more amps than at 90% as in the OP.

If the higher 14.x Vabs will stay on till batts are "full" (usually taken as about 97-99%) then no need to swap chargers till then, so the finish charger could be lower in max amps than at 90% as in the OP.

I would think that to only top charge a lead acid battery or pair of batteries, the smaller 20 amp supply would be all that's necessary. If the price between 20 amp, 30 amp, and 40 amp is trivial, there's no reason not to choose the bigger supply as you can do more with it. It may even be appropriate to gang two of them to make a charger that will make the full course dinner for the bank. I think Mena is contemplating something similar.

FWIW, my Enersys AGM batteries have no limit as to amps in the charge cycle, i.e. until full charge is reached.

It does not say not to exceed it, just that 10% is the 'recommended' initial bulk rate.

I've allowed my alternator to give this SOB 75 amps. Next biggest charging source I have, until tomorrow, is 25 amps from the pSyChumacher.

A group 31 is recommended by OEM not to exceed 13 amps in bulk stage? Either I read this wrong or certainly it is a misprint.















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I'll be using my 30 amp MW clone for bulk, ABSorption, Finish and Float on a 91 AH AGm or on my 130AH screwy31 which requires the 15.3v after every cycle or it nosedives

Supposed to be here tomorrow.

The AGM responds well to high charging currents. The 31 is recommended to get 13 initial bulk amps. So 30 amps is well outside outside this 'recommended' range but I am hammering this battery anyway so babying it might just confuse the poor thing.

BFL13 wrote:
Scenario is you are on shore power and your regular charger (limited to 14.x volts) gets the batts to about 90% SOC, then you apply your special finish stage charger that can do 15.x volts but is limited in amps.

(This might apply to a solar controller too but generally you would not do this on generator due to the long run time when charging at over 90% SOC.)

Using the marker of 5 amps per 110AH of battery for acceptance rate at 14.4 volts at 90% SOC, the question is what would be the acceptance rate if you cranked the voltage to 15.5 at that point? That would tell you the highest amps size of finish charger it would be worth getting---knowing how many AH of bank you have.

Ok I ran a test on my 458AH bank using my variable voltage charger where amps got down to 21a as my marker for being at 90% and voltage was 14.4 (458/110 x 5 = 20.8)

I then jacked up the voltage on the charger to 15.5. Battery acceptance jumped to 34.3 and battery voltage to 15.1. Within two minutes, amps were down to 31ish and tapering with voltage 15.2ish.

So very roughly, it would seem sensible to have the 15.5v finish charger be able to do about 32a for four batts so call it "30a" for charger size. and so that would be 15a for a pair of batts.

No point in going larger in amps when the batts won't accept any more amps than that. Amps were tapering so you could say to go even lower in max amps for the little time it would stay at 30 or 15. For the money and time, optimum might even be say, 20 and 10.

Anyway that is sort of what you are looking at in that scenario, it seems.

If it is a top charge I would think you would hold the 14.4 to 98% to 100% then do a top charge. 6 to 10 amps would be plenty IMO for your 4 batteries. Better to give these batteries a bit more time IMO.

To add to Landyacht, MW threads are all about the top/finish charge although some are using it as a ABSV charger cause their converters cut out too soon.

I think the equation as to how much MW is needed depends so much on the 'other' charging source, that one should just have more than enough MW to hold ABSV.

Not much price difference between a 20 and a 40 amp. If the battery only needs 20 amps to hold ABSV when the primary charging source has declared "enough!", then having a 40 amp power supply is not going to hurt.

Likely the amps required to hold ABSV will change through out the lifespan of the battery. Not sure how much it will change but my screwy31 thread should have the data within 6 months to a year if it can handle the abuse I keep subjecting it to night after night.

Perhaps I have misunderstood the MW threads, But I did not think it was to force ABSV into the mid 15's. Time in the mid to high 14's for it to absorb, then a topping charge in the 15's to top/finish charge, and perhaps on some batteries this might fall into the regular EQualization profile which makes so many of us nervous we crawl into the 14.4v corner and chant that PD knows what is best for every battery always.

If forcing the battery upto 15.56v as fast as possible was the goal then there would be no point in stressing about how easy/difficult it is to adjust the voltage with a finger turn pot. For proper MW assist, it needs to either take over from the other charging source and hold the most desirable ABSV for x amount of time, then have the pot adjusted again to ~15.5 for that top charging that no lawyer will allow any automatic multi stage charger maker to just hold all day long.

OK I must have got mixed up reading all those MW threads, but I thought I could at least answer one of the questions. I do remember people asking how big in amps of a MW they should bother getting.

So somebody get serious and figure it out for real. :( :)