Stanley Fatmax 8amp Automatic Charger

[TimothyP]

Has anyone ever used a Stanley Fatmax Automatic Charger in place of a 110v power supply? Literally everything in my trailer is powered by two Group-27 12v batteries. Most of the time I recharge using solar power (100watts potential). When there is no sun and I have 110v available I want to be able to charge my batteries by plugging in. The Stanley charger has the capability of sensing when the batteries are fully charged and it will reduce the charge current to trickle when they reach full capacity.

Recently the control board on my DuoTherm furnace failed. I was plugged into AC at the time and, even though my furnace is connected to the batteries, the Stanley charger was also connected to the batteries. Could the pulsating DC from the charger have blown my board or was it just an unfortunate coincidence? I know that you can't run the furnace on a battery charger but I was of the impression that the presence of the batteries canceled the pulsating effect of the charger.

Someone with a superior knowledge of electronics please enlighten me.

[The Minimalist]

Originally Posted by TimothyP

Could the pulsating DC from the charger have blown my board or was it just an unfortunate coincidence? I know that you can't run the furnace on a battery charger but I was of the impression that the presence of the batteries canceled the pulsating effect of the charger.

You may want to check the documentation on the charger. My Stanley automatic charger only uses pulsating current during the reconditioning cycle.

I think you're right that the battery should dampen any pulsation from the charger, assuming the battery has a good charge on it to begin with.

[TimothyP]

Dear Minimalist

Thanks for responding. I am encouraged by the fact that you agree with my interpretation of DC pulsing being negated by the presence of my batteries. I know that they are strong because they measured 12.5v - 12.7v under load at the time.

The data sheet that came with the charger is useless. It appears to be nothing but a CYA document by Stanley full of warnings about the obvious but with very little useful information. You mentioned that you use an automatic charger also. Would you mind telling me what brand and size it is? I gather that you haven't had problem with DC pulsing.

Alternatively, I could just install a DPST switch which would disconnect the furnace and connect the charger when the charger is in use. Conversely, it would disconnect the charger and re-connect the furnace when the furnace is in use. We generally do not use the furnace when we have AC power available because we use an electric space heater to save gas. However, I would prefer not to have to go through that hassle if I can avoid it.

Thanks again for your response.

Tim

[The Minimalist]

My charger is a Stanley BC25BS which has a 24 hour reconditioning cycle which does pulse the charge to break down any sulfate crystals that may have formed in the battery. In a quick on line check, the Fat Max 8A automatic chargers I found don't have the reconditioning feature.

[Franswa]

I think you may be jumping to conclusions attributing the failure of your heater control board to your charger....where's the proof of that??

if you connect a charger to battery posts and main leads are connected to same battery posts....how is a battery supposed to stop "unfiltered" power from flowing to your whole system??? unfiltered power is not suitable for radios or televisions because it will induce a "hum" in the audio.....I have not heard that unfiltered power causes damage to cuircuit boards. I have been running my system with no converter/charger for three years now and using a smart charger instead....I have not blown/lost a circuit board in that time....and my radio runs fine (leads me to beleive that the warning about "hum" is kind of old...as in with electronics with tubes in them...but I dunno for sure)

While your charger is "good"...it's not the "smartest tool in the shed"....and at 30 bucks you should not expect it to be. It will work however. The difference between it and smarter chargers will be the length of time before you have to replace your batteries. That is a very hard/impossible one to quantify.

The manual you got states what the charger will do....will charge your twelve volt battery in your car or motorcycle and will not ruin them by overcharging them. That's it....as mentioned before smarter chargers do a little more to maximize the number of charge/discharge cycles that the battery manufacturer suggests before the batteries die of pure old age.

as an aside, having two group 27 batteries in a 13 foot trailer should win you sort of a prize !.....Man, that is a LOT of batteries/weight for such a small trailer....I'll give you that!

below is a pic of your instructions (relevant part) and the charger I use (which costs substantially more than 30 bucks)....

Happy trials, F

[TimothyP]

Dear Franswa

Thanks for your response. You have confirmed what I had suspected all along. There is no problem using the Stanley charger under the circumstances that I use it. I spoke with a cousin earlier today. He works for DTE which is the local power company here in the Detroit Area. He also has restored several vintage RVs. He explained that the battery wired parallel with the charger functions like a big capacitor and it filters any DC pulsating that may occur. It is very unlikely that any damage could/would occur. Additionally, I believe you are right about modern smart chargers being less harmful than the older ones.

I believe that the small 8 amp unit that I am using is adequate for my purposes because the largest load I place on the batteries is from the furnace which draws about 3 amps. Along with a few LED lights and a cellphone charger, the greatest total load I place on the batteries is about 5 amps. If my charging potential is 8 amps, it should be adequate to keep the batteries at a safe level. Also, the smart charger is not the primary charge source for the battery. The solar panels are. The Stanley charger only functions as an auxiliary source when I have AC power available. I mostly boondock.

One of the reasons I carry two group 27s is because a couple of winters ago I got stuck in a truck stop in northern Kentucky for two nights. The temperature dropped to about -15 degrees Fahrenheit both nights and the furnace ran most of the night. It warmed up to about 0 degrees in the daytime so the furnace ran most of the day also. There was no way to recharge the battery except for the little bit of low level sun available in the Kentucky winter sky. The battery voltage level dropped into the 11v range and I am sure the battery was damaged. However, with two batteries I seldom go below 12.5v. Weight is not particularly problematic as I have the second battery mounted over the axle area and U-Hauls are notoriously over-built. I'm not worried.

Thanks again for your wisdom. I do appreciate it.

Tim

[Franswa]

it all makes more sense to me now.....I had assumed you had a convential built-in converter/charger as well.....now I found out we both run our systems the same....no conversion of AC into DC except what goes through the charger....IMO that is a "cleaner" sort of system...simpler to understand/estimate what is going on....especially when you add solar to the mix

when I first got my trailer (my first RV) I realized that my TV was not sending power to the coach...so that got put on my "list"....but then after a while I took it off my list for the reason stated above

I spent a LOT of time fiddling with electrics on boats...small cruising sailboats...but that is very different as you have the alternator of the outboard running, at a very minimum, half an hour at the beginning and half an hour at the end of the day.....power was never a problem but there was no furnace to consume large amounts of DC power either

yes, I agree 8 amps is plenty for our use...I have 7.2 and it's probably more than I needed even...but my next choice was 4... and the price difference was small in the whole scheme of things

FWIW...I, like most people I presume, got in to solar by dribs and drabs...adding this, changing that, relocating panels, buying when I saw a good deal ($ per watt).....I now have 70W (40+30) flat on the roof and a 40W I can deploy (aim to the sun perfectly when parked) and so far I have found it more than adequate for me. In fact if it's high noon on a sunny day and the 40 is out too I could probably sell power to my neighbours!!! because the controller maxes out...but it's a help on marginal days...

I was just out for a week...half of the days were sunny...rest cloudy...never plugged in...deployed the 40 only once...and at rest my batteries never went below 12.45....and even then the culprit was recharging the laptop which is a surprise "power hog" that I should get into the habit of recharging in the TV as I tend to move every day. The rest of the week the meter was always around 12.5 when I woke up.

it'll be interesting to see how it all works in the fall when the furnace gets used sort of regular....but right now I seem to be sitting on quite a comfortable "buffer" to handle the extra load...I think

cheers, F