Agressive Schumacher speed-chargers

[PNjunction]

Just a quick warning after a friend boiled his brand new agm for 3 hours with one of these on the agm mode ... (wish he would have called me because I went through it myself)

Went through three chargers around the neighborhood that like to go into high voltage EQ voltage on well-maintained batteries on their own without user permission: SC-1000A, SSC-1500A, and a SC-7500A.

Essentially, they eventually like to go .7V too high on each setting, usually pushing them well over 15 volts and way too soon, which in the case of agm's and especially gels is usually not recommended by the manufacturer. However there is a workaround for this aggressive behavior. The units that had a voltage display option were at times not accurate - a Fluke 87V voltmeter across the terminals told all.

1) Don't ever use gel batteries with these.
2) Use the mildest setting "gel" for agm and flooded. Apologize to friend for confusing him about using gel mode when his battery is really agm.
3) In reality, choose the best measured voltage, and not the labeling for your application.

In the gel-mode with my agm's that like to see 14.7v absorb guess what? Yep, 14.7v absorb was reached which tapered down to 14.4 volts at the end of absorb before going into 13.6v float. And that's gel mode! My Optimas and Odyssey's like it. It might be a tad too high for lead-calcium agm's like East-Penn/Deka, but at least it is no longer pumping out 15+ volts with the resultant snap-crackle-pop heard inside the battery for 3 hours.

If you mistakenly start out in a non-gel mode, disconnect cabling and start again - seems that merely changing the battery mode while powered up doesn't convince them not to do the high-voltage treatment.

This gel-only-mode workaround seemed to work best on the chargers that had non-sliding amp selections - that is, the 7500A has a sliding 10<>20 amp mode which oscillates back and forth when charging. Unfortunately, even when set to gel mode, when it oscillates to the 20 amp mode for a few minutes, the high-voltage treatment is back, even though you have overriden it with the gel mode. The smaller 1000A and 1500A worked like a charm.

Obviously a higher-quality non-automobile charger is a better idea - along with solar and a decent controller. But if this is all you have, please try one run in gel mode even though you aren't using gel batteries. It could save you some $$ and actually have a useful charger in the end.

[PNjunction]

A follow-up call from my racer-x friend "but I was told never to use the gel/agm settings on my agm!"

That would be true IF the charger actually used low 14.1v or so applicable to gel and too low for agm in absorb. In the Schumacher case, it may go well the other way well beyond that into the mid-15's when set to agm ! "but, but, but"

But nothing - don't trust me, trust your external quality voltmeter. Specs are often unpublished and subject to change and manufacturer variances. Go by measured voltages and not assumptions even if well-intentioned. Other chargers may act differently even among the same brand.

This he understood: "yesterday you just did a 3 hour burnout with no traction (high voltage gassing instead of actual charging) all the way down the track".

Use your tools, like a quality external voltmeter. Ah, NOW he's ready for solar!

[PNjunction]

Quick addendum: the most stable voltages and best absorb characteristics only occurred when running the SC-1000A and SC-1500A in their highest amperage settings using this gel-workaround.

Tracking this behavior is getting less fun as time goes on. I think I'm done with the Schumachers.

[PNjunction]

I guess I'm not done.

Scrounged up a new 2/4/6A SC-600A and put the screws to it with a voltmeter and clamp-ammeter. There is no chemistry setting, just amperage and volts (6/12). I note that the box makes no mention of being suitable for gel, only standard and agm.

Nice. 14.8v during absorb. Absorbs all the way down past 100ma where my meter is no longer reading much. Goes into float-monitoring, not a true float charge. No wonder gel isn't on the box. My agm's don't mind this at all although I really want to put a 13.6v or so float on it from my solar setup or a dedicated maintainer to truly finish the charge.

In nearly all cases with all of these chargers above, if you try to use them as maintainers on an already charged battery, you'll see ramping up to 15.5 volts or more at significant currents. This SC-600A wanted to maintain my already charged agm at nearly 2amps at 15.5v, even in gel mode, so I'd only use if it the battery has actually been discharged at least 25-50% - which tames it down and seems to act properly. I think the schumacher thought my battery was badly sulfated - which it was NOT being only 30 days old, and passing 20 and 5 hour discharge tests.

I can only guess that the Schumachers agressive behavior is for those who are already in BIG trouble with their batteries, and agressive behavior may get their vehicle moving again. For batteries in *normal* condition, only the lowliest GEL setting seems appropriate, even if this label does not exactly match your battery chemistry. With proprietary undocumented algorithms, only a voltmeter and ammeter can give the layman half a chance of meeting a battery manufacturer's spec.