24 vDC solar charger on a 12 volt battery

[nunnery_james]

I have a Pulse Tech 24VPSC solar battery charger (I got for free) and I was wondering if I can safely use it to charge my 12 volt battery in my trailer? Its an Optima battery that I use for lights and the emergency brake.
Thanks in advance!

[Naptown]

maybe it is for 24V batteries but the wattage is so low it may not matter

[Sunking]

Ye can get away with it but you are fooling yourself. The charger is so low power it would not hurt a AAA battery. The fooling yourself part is thinking it will charge your battery. Not going to happen.

[nunnery_james]

Here's the link to what I have:

http://www.pulsetech.net/24VPSC-PulseTech-Solar-24Volt-Battery-Charger-Desulfator-7303.aspx

[Sunking]

Here's the link to what I have:
http://www.pulsetech.net/24VPSC-Puls...ator-7303.aspx

Again we understand. You not so much. It is a POS. Go ahead and buy it. No better way to learn than spending your money if you do not listen.

Minimum requirement for the battery in Question is a 120 watt solar panel with a 10 amp Charge Controller. A 3 POS watt panel will not even charge up a cell phone battery.

[nunnery_james]

Again we understand. You not so much. It is a POS. Go ahead and buy it. No better way to learn than spending your money if you do not listen.

Minimum requirement for the battery in Question is a 120 watt solar panel with a 10 amp Charge Controller. A 3 POS watt panel will not even charge up a cell phone battery.

Dude, it was free.
We use it on our USMC MEP831 generators to prevent the batteries from dying between uses do to parasitic loss. Those batteries are Hawker 12 volt batteries wired together to make a 24 volt system. Hence why the charger is a 24 volt.
I'm not trying to start an argument but it seems like I'm getting fired upon.
I guess that's what I get for going to what I thought was a knowledgeable source and asking an honest question.

[Sunking]

Dude I am former USN Officer. Get over it soldier. I give Grunts Hell when I get a chance, that is what I was paid and trained to do. Get over it. I am giving you straight advice like an NCO trainer. I do not care if you get your shorts in a knot. All I care about is get you through the battle in piece to fight again. Difference here is i do not get paid. Other than that I am a professional Electrical Engineer after service.

What you are looking at is a very low power battery maintainer made to keep a fully charged battery topped off when not in use if there is no commercial AC power available with a standard AC charger like in the field. Sound familiar? It is not capable of charging the battery in question, just keep it from dieing in the field like a Corpsman.

So if all you want to do is throw that battery in a shed in the middle of no where to keep it charged up, have at it. Otherwise keep it on a regular AC charger is you have AC power. You are dismissed

[PNjunction]

I can dig it - you know the deal between a charger and maintainer obviously, but even for a freebie, this thing is $300 retail!

My initial thought is that even as a maintainer, I wouldn't let this 24v unit touch any of my 12v Enersys - Optimas / Hawker or JCI-Optimas. My main concern is that even at very miniscule currents, when you are at the very end of an absorb cycle from a real charger, where applying a followup maintainer like this would actually do any good, you'd be applying too high of a voltage and corroding the plates, defeating the whole maintenance aspect.

You may not see the voltage rise at the terminals immediately, but the dinky little panel is still trying to bring a 12v battery up to 24v, about 10 volts higher than they should ever see!. In my mind, that is not good and may accellerate grid corrosion and is one reason that I run charge controllers even on small 12v nominal (18v or so ocv) solar maintainers. If you want to look into this, search for "Enersys grid corrosion intermittent charging".

So I guess ask them and see. I'll bet they'll advise using a 12v unit for 12v batteries, but who knows with proprietary stuff?

[Sunking]

My initial thought is that even as a maintainer, I wouldn't let this 24v unit touch any of my 12v Enersys - Optimas / Hawker or JCI-Optimas. My main concern is that even at very miniscule currents, when you are at the very end of an absorb cycle from a real charger, where applying a followup maintainer like this would actually do any good, you'd be applying too high of a voltage and corroding the plates, defeating the whole maintenance aspect.

I do not think that is remotely posible with a lead acid battery of any size say above 50 AH. The internal impedance of a charged up battery is so low in comparison to th esource impedance of the panel it would be impossible for the panel to ever approach Vmp voltages. The battery would have to go to almost open circuit for that to happen. The source impedance of th epanel is up around 200 Ohms. A good 50 AH 12 volt battery impedance is in the milli-ohm range. Battery impedance would have to go higher than the panel impedance. That would be a dead sulfated battery.

[PNjunction]

The internal impedance of a charged up battery is so low in comparison to th esource impedance of the panel it would be impossible for the panel to ever approach Vmp voltages.

So that explains why totally underpowered bare panels of 18v ocv or so can be attached directly to a large 12v battery! It isn't a good charger at all, and being hampered by impedance (still represented as "Z" in solar land?) the only thing it is good for is perhaps offsetting tiny parasitic drains - essentially maintaining the SOC that the panel found the battery in.

HOWEVER, if you are getting what appears to be a charge from a totally underpowered directly connected panel, (like C/300 or more) and find yourself reaching the panel's OCV point, in reality you might be dealing with a hard-sulfated battery, one that is basically much smaller than what you started with, and C/300 is no longer realistic - you may be well above that due to the loss of capacity from sulfation. Of course the claim here is that your battery is magically healed, yet won't pass a load-test.... hmmm..

Cool - thanks for the info. That might be a handy little diagnostic - put a joke of a panel directly onto a battery and if it reaches ocv levels, you've got problems.

In nunnery_james' case, I'd still be worried about 24v to 12v issues if the active circuitry of that maintainer then presents a very low impedance and now maybe you will eventually end up going overvoltage...gotta' think on this one some more..

[Sunking]

In nunnery_james' case, I'd still be worried about 24v to 12v issues if the active circuitry of that maintainer then presents a very low impedance and now maybe you will eventually end up going overvoltage...gotta' think on this one some more..

PN here is the other thing. The controller is PWM, and as we know PWM is really nothing more than a relay or on/off switch which connects the panel directly to the battery right?

The panel in question is a 24 volt battery panel with a max current .225 amps. OK with a max current of .225 amps on a 12 volt battery = 2.7 watts. The panel rated wattage is 6.5 watts. That is what happens with PWM. Very little chance it could damage the battery, and no chance of charging it. If anything the charger might get damaged, but not the battery.

Back to a point you made. Back in th eole days of solar before it started gaining traction in the late 90's and early 2000's solar battery panels for 12 volt batteries were only 28/32 cells with a Blocking Diode vs 36 cells today w/o blocking diode. They were intended to either be connected directly to the battery terminals or use one of the relay controllers like Coleman still makes to day. The irony is those systems were more efficient than today using PWM controllers. The down side of doing that is very little voltage control, where PWM does offer precise voltage control, and allows the panels to supply power to the load when the power is sufficient and the batteries are fully charged up.

A 100 watt panel back then would supply up to 7 amps of charge current vs 5.5 today with PWM. Makes you scratch your head huh?

[PNjunction]

Ah, right. You see the pulsetech chargers/controller frequently (solar, shop, nato-connectorized etc) around the Hawker / Optima mil supply sites. From their own documentation, it does indeed appear to be pwm, but incorporates some proprietary sawtooth pwm waveform instead of just a normal pwm duty cycle with a "fat" square wave. I'll leave the marketing side alone....

I think the standard Morningstar pwm controller uses up-to 300 hz mosfet switching - I could be wrong though.

From what I remember, yes those old-school panels that had 28/32 cells were so-called "self-regulating", but the problem was that in hot temperatures their efficiency fell far short as the voltage dropped sharply rendering them useful only in cold climes. At least that was what I was told.

I just hope nobody goes taping-off or shading 6 of the cells on their existing 36 cell panel of today.

[Sunking]

PN any of the claimed Desulfators are PWM as it is just the nature of the beast. They Pulse Wave Modulate.