Temporary use of a Walmart portable marine charger at dock?

[SoulVoyage]

I used the search engine looking for threads on portable charger viability, to no avail...so here goes my query:

My onboard shorepower charger recently went kerplunk (might be diodes, might be windings, who knows?), and until I either: 1) take it apart and ascertain what's wrong with it, 0r: 2) buy a new multi-step "smart" charger (if I can find one at a decent price, that is!), I am wondering about the eficacy of temporarily using a Walmart "Ship & Shore 15/10/2 amp" portable "marine" charger to charge my system while at dock. I see nothing in the documentation with the thing about any type of internal isolation, but that doesn't necessaily mean it doesn't have it. It's a $49 "marine" portable marine charger, so I figure it's gotta missing something.

My present system: Bank #1 = 1 separate 12v 24 series 500cca starting battery; Bank #2 = 2 100 ah deep cycle house batteries connected in parallel. The two banks are seperated by 4-way batt switch. There is also one emergenncy 12v 24 series starting battery kept on a solar maintenance charge, and one emergency 12v deep cycle instrument battery on a seperate solar maintainer.

My usage: At dock - 4 small incandescent lights (2 amp total draw or so); stereo (can't be more than 1 amp, I'd guess)...so 3 amp maximum total, or could be much less. All my water is manual pumps. And right now reefer unit is down for the count, so zero amps there . Underway: VhF radio on scan standby; stereo; depth sounder (Hummingbird), Garmin GPS; very rare radar usage(simrad 18"); tricolor running lights under sail, powerboat running lights otherwise; no more than 2 cabin lights at a time, augumented with kerosene/oil lamps. That's about it. All sailing gear is manual. No reefer use underway or at anchor.(hey....not THAT kinda reefer!); 75 watt inverter for notebook computer. And VERY occasional use of a 150 watt inverter for charging E-Cell AA batteries.

In short, either at dock or underway, my electrical load isn't huge. Barely use radar underway.

What I would like to do, then, while at dock is to temporarily use that walmart portable charger. By temporary I mean I won't have charger online 24/7 while aboard like I would with my regular AC charger. I would go off charger, monitor the housebanks to 50 - 60%, put charger back online at 8amps medium setting(it has 15 amp maximum), then take charger offline again as it nears 100%. I would charge starter battery with it separately.

I can't see this format as that much different than being at anchor and using engine every 36 hours to charge batteries. The main thing is to keep that charger offline when not actually needed.

Would using this portable charger in only such on/off format be doing any damage to my 12 volt system galvanically...as the batteries ARE hooked up to my 12 volt wiring while shore-charging? Is this a no-no with a portable charger, due to some aggregate galvanic situation? I've never needed to rely on a portable unit before.

Truth-be-told, I would rather spend money on a new main, and a trim-tab self-steering, and things like solar panels than on a dedicated shorepower charger, if this portable will work...it is supposedly a 'smart-charger' and will automatically go into maintenance monitoring and then re-'step up' the amperage if it senses a load...it just isn't a multi-stage unit. bulk and all that.

Problem is: it's now been on for 7 hours on a 2 battery, deep cycle 200 AH, house-bank that started at 70% and after 7 hours at 8 amps it's at a whopping 78%!! Wow! And that's with NO load on household bank at all. Been using headlamps! I could switch to it's maximum of 15 amps, but I always thought that too much amperage can kill a battery if their is no load on it.

I realize it takes far longer for the last 20%, but it hasn't moved from 78% for HOURS now! Bad purchase?

Anybody have experience with these silly Walmart portable chargers? I just bought it last night. It's a Shumacher "SpeedCharge" SSC-1500A. Ha ha...."speedcharge"!! Yah, right!

[xsboats]

I would put it on full charge. Then bring the bank back up. Finally , I would calculate my consumption, and put a timer on the power supply cord for the charger set for an approximate time that multiplied by the amperage will match your consumption daily. You may have to reset a couple of times before you get it right.

[mitiempo]

I see no problem if monitored. It will be slow as you say. The problem is that it may boil the batteries if they are fully charged and it is left on. If you are using a good battery monitor (you'd have to be to determine 50 to 60% SOC) you will know when the batteries are close to 100%. Then turn it off.

[Estragon]

+1 on putting it up to full 15a setting, at least initially. It seems likely to me that putting it on a lower setting is eliminating the "bulk" phase, in which a higher voltage is applied. The amperage will be limited by the (lower than charger max) acceptance of the battery, would it not? The 10a setting probably outputs a lower initial voltage for an aborption phase, then kicks down to a maintenance phase, possibly after some predetermined time. I'd check output with a volt meter to confirm.

[SteveInMD]

I looked at the Walmart website...

Walmart.com: Schumacher SpeedCharge 15-Amp Marine Battery Charger: Hunting

It's supposed to be a fully automatic charger. You should be able to leave it on the 10 amp setting for extended periods, as it should reduce the voltage as the batteries come up. Keep an eye on the voltage. As the batteries charge (which might take as much as 12 - 18 hours) the voltage should drop down to 13.4 ish. It it doesn't don't leave it on that setting. You should be able to leave it on the 2 amp setting for a day or two with no adverse effects.

[Maine Sail]

I own own of those chargers and it is a certified POS. Mine wants to regularly charge my batts at over 15 volts. I returned it shortly after buying it and the new one does the same thing. I bought it for some bench experiments and it was a total waste of money. On the small battery 2A setting it seems to work ok but on the 15A mode be careful..

I would invest in a small Iota charger...

[scottyt]

i have the same charger and it works great. i have monitored the voltages it puts out and when it shuts down and they are accurate. now i am not on constant shore power so its not all ways on. i even tried to get a reading with my DVM on AC and did not get a reading so it does not leak or leak much AC

[SoulVoyage]

So far it seems to work. I am not sure if it is a dedicated 3-step charger (you get what you pay for), but it's automatic testing procedure seems to work. It has brought back to life a 27 series deep cycle that I was about to haul off to the dump for showing no specific gravity after "charging" for 6 hours with my other charger. It now seems fine. Granted, being "flattened" a number of times will shorten it's number of lifetime charge cycles, but it still has whatever number of cycles left.

I figure as long as I monitor the input voltage during charge and abide by the "50% Law" when the banks are not on the charger, it should work. Like I said, I don't have a large DC load...no water pumps, no electric windlass, etc. At dock, just lights and stereo. A few instruments when under sail plus lights and radio.

It might even be a good thing losing my dedicated onboard charger, as now the responsibility for maintaining my batteries rests solely with me, as it should have been in the first place. I find I monitor the battery state now MUCH more. I have a decent battery condition monitor, just a simple analog meter, but it works well.

I think I learned my lesson with the 50% rule!!!

[ekenna]

I have a similar 2,10,15 charger. I always start it at 15. It will quickly dial down based on the battery state. Beside you said it is like running your engine while at anchor. Well my alternator puts out 55 amp. I am assuming my regulator on my alternator does all the checking of how much the battery can take.

What no one commented on is "damage to my 12 volt system galvanically..." My only comment would be disconnect the battery while charging it.