I have 2, 12v AGM batteries that I use in series to run a 24v motor. The system has a solenoid controlled by an on/off switch that interrupts the power from batteries to motor.When not in use, the switch is off. Am I correct in thinking that the batteries are not considered to be connected in series at that time?Except: There is a 24v charging port on the system, which connects to the batteries via tiny (18ga?) wires. THAT is the only thing completing the circuit.I usually use a 24v charger, but sometimes use a 12v (connect to one battery, then to the other, till full or for a set period of time).I was thinking that I could use a solar or alternator-charging setup the same way I use the 12v charger. But then pianotuna said some stuff I do not fully understand:The charging of one 12 volt battery followed by the other one may cause them to become out of balance which would require more frequent equalization...Balance is a whole bunch more important that most folks realize for longevity of a battery bank.I understand that one battery might be at, say, 12.9 and the other at 12.97. Is that what is meant by balance? Frankly, this happens all the time with the 24v charger - maybe because my batteries are old? They still perform very well.And what does this have to do with equalization?Then smkettner said I should get a switch to switch them from series to parallel.But I had not mentioned the solenoid to these/you guys. I only thought about it later. Does the solenoid make the whole issue moot, or do I still need to think about a switch and balancing?

If the batteries are dedicated to the job there is nothing at all wrong with charging them individually. CAVEAT Make sure the batteries BOTH get charged 100% and do not run the pump while you are charging one or both.

Naio wrote:When not in use, the switch is off. Am I correct in thinking that the batteries are not considered to be connected in series at that time?A little difficult to answer without a schematic, but, unless your switch is on the battery interconnect cable, no, they are still connected in series. Whether they're powering anything is irrelevant. Does that answer?

the are 24v series usedthey should be 24v series charged..for best resultsthey are still in seriesyour power solenoid is between the batteries and the motornot in between the batteriescan you charge them individually yes.. is it the best way NO!

2oldman wrote:Naio wrote:When not in use, the switch is off. Am I correct in thinking that the batteries are not considered to be connected in series at that time?A little difficult to answer without a schematic, but, unless your switch is on the battery interconnect cable, no, they are still connected in series. Whether they're powering anything is irrelevant. Does that answer?I hesitate to try to do a schematic in ASCII.There is a cable connecting A- to B+.And B- goes to the motor.But the cable from A+ has a solenoid in it, so it goes nowhere when the solenoid is off.Does this count as series?And what exactly is the bad thing that happens if I charge them seperatly?Or simultaneously, on two 12v charger outputs?

Naio wrote:I hesitate to try to do a schematic in ASCII.Does this count as series?Ascii? Use a graphics program like Paint.As long as there's a cable from A- to B+, yes. I really don't know what the point of your question is.

Series/parallel charging question for les tinkerers grandes

Naio
Explorer II
Jul 02, 2015
Salvo, I know better than to try to run the freezer off a battery.

Made that mistake once with a 12v fridge... that was how I found this forum :).
Salvo
Explorer
Jul 02, 2015
Temperatures in the van will be in the 90's. The freezer will have a duty cycle of perhaps 1/3 from the get go. Freezer pulls 10A when on, or 8hrs * 10A = 80AH per day. The 170AH battery (when is was new) gets pulled down to 50% soc just from the freezer alone. The battery will probably never get charged to 100% while on the gen. After 5 days the battery won't look too good.
MrWizard
Moderator
Jul 02, 2015
It will do three days after being plugged in for 24 hrs
Then a few hours every day should extend that period maybe to a week ?
Salvo
Explorer
Jul 01, 2015
With one small 12V battery; a disaster! But you'll learn one way or another.

Naio wrote:

I don't know what it would do if plugged in once a day for a few hours daily while charging batteries.
Naio
Explorer II
Jul 01, 2015
If the freezer is plugged in for 24 hours, it gets very cold and keeps things frozen for 3.5 days at moderate outdoor temps (low 70s).

I don't know what it would do if plugged in once a day for a few hours daily while charging batteries.
MrWizard
Moderator
Jul 01, 2015
The generator can cool the freezer while charging the "pair"
And since there is also a regular portable battery charger the existing house battery can also be charged IF needed
Solar can be added later IF wanted
But at the moment it's appears to be an either/or situation
Salvo
Explorer
Jul 01, 2015
What about the big picture? Still need a freezer to feed the ice shaver? ;)

With your small 12V battery (not motor batteries), the gen will have to run much of the day.

Go solar. You'll need 4 x 6V batteries to make a 24V system. Without large energy storage, 400W solar is foolish.

BTW, I can attest to the heat wave at the Columbia River Gorge. It's been the hottest June!
pnichols
Explorer II
Jul 01, 2015
Here's the generator we use ... unfortunately this particular one is in the wrong country ... but you could look around to find one used (they're a discontinued - but legendary - Honda product), cheap, and available in the U.S.:

http://www.gumtree.com/p/generators/honda-ex650-suitcase-generator/1123007002

Here's a spec chart showing how it stacks up against other discontinued Honda generators - from the chart, notice it's noise level - as compared to the current Honda EU1000i generator's noise level:

http://www.tappedin.com/hop/html/litegen.htm

Here's one model of the fuel cell RV battery charging technology I was referring to - methanol powered. Note that's it's output power is 28 VDC (check the Tech Specs tab):

http://www.protonex.com/products/m300/
MrWizard
Moderator
Jul 01, 2015
nice quiet 1000w fuel cells are/were available
but the price of their specialized tank of alcohol, makes it a damm expensive operation to use

what we need is "Mr Fusion"
Naio
Explorer II
Jul 01, 2015
Thanks, pnichols. I've been feeling awfully bummed tonight at the idea of spending $1000 on something that is not really what I want, but you made me feel a little better.

Fuel cell, eh? Is that actually a viable option? Or do you mean in the future? A quick google looks like not yet...

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Series/parallel charging question for les tinkerers grandes

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