running two chargers

[jbeliera]

Here is a technical question. Let's say you want to charge your house batteries on your RV quicker. If you have two 12 volt batteries in your battery bank would you charge that battery bank quicker if you put two 25 amp battery charges on at the same time. Would that be possible to increase charging amps and less charge time or would it fry your batteries

[Cydog15]

ScottG wrote:

2oldman wrote:
OK, yes, parallel batteries might do better separated. Series, no.

Remember, the discussion is about using two chargers. Trying to use two smart chargers for either parallel or series batteries never works well if the two chargers are in parallel.

That's just not true. We use parallel Boondockers all the time. Also PD and others. It does work and many OEM send out units like that as well as fleet vehicles.

[full_mosey]

ktmrfs wrote:

Dirtpig wrote:
I feel like it would be much less of a hassle to just upgrade your converter/charger to a 75amp/100amp model. No Mickey mousing clamping or disconnecting batts. Just my 2c.

well, since I have a 2000VA generator, it will NOT run a 75 or 100A charger. so, I have a 55A charger in place of the WFCO and a 65A in the pass through. when only on one generator, on goes the pass through 65A. when I have shore power or two generators then I crank them both on and get 110A or so for quite a while.

So, there are reasons to have two chargers rather than one.

and there is no mickey mouse stuff, I just turn one or the other on or both on. both are connected to the same battery bank in parallel.

75A on 15A line, 1260W.

Any good?

HTH;
John

[MEXICOWANDERER]

I could have run 20 Km marathons daily, become Vegan right out of the womb, and purchased a hundred dollars worth of vitamins and supplements monthly, all for the objective of gaining lifespan.

For me. My lifestyle?

Hahahahahahahahahahahahahahahahaha...

Shirley you jest. I would have been a sure target for some malfunctioning transit bus.

A manufacturer CAN NOT RECOMMEND constant voltage saturated charging because CHARGERS CANNOT DO It.

As fuel prices rise, my wallet tightens in response. The best way to preserve a battery is to pour a ton of money into it's maintenance and get tinnitus from hundreds, nay thousands of hours of excessive generator run time.

There is a CURVE exhibiting lifespan versus charge amperage limits. It is most pronounced between 10% of amp hour capacity and saturated charging. Under lab conditions it is something like + - 10%

This is for a ten % min and perhaps 45 ampere max charge span.

Factor in generator annoyance -- generator wearout, fuel, and logistics costs then try and defend so-called "ideal max charge rates"

"Uh raised muh oan tomatoes. Can you taste the difrunace? Doan wanna talk about the cost -- pretty touchy abut that"

I tend to think more about amp hour consumption versus recharging costs to replenish. You know -- a hundred dollar battery versus five hundred dollars to recharge. In deep double-canopy shade.

My car engine would last longest if driven at exactly that speed where the transmission switched to overdrive -- 42 mph. But then if I can listen to a generator hammer 3 extra hours every recharge -- I can leave the car parked and use a unicycle (less footprint).

[ktmrfs]

wa8yxm wrote:
3 answers. one is a caution.

In the manual for my Prosine 2.0 Xantrex suggests a maximum charge rate of 30% the C/20 amp hour rate. so if you have say one pair of 110 amp hour GC-2 batteries in series (still 110 amp hours since in series you add voltage) that would be 33 amps max charge. Or less for most battery types. Or more for LIFELINE AGM only.

Second answer: If you have enough battery it will not HURT and no damage will happen but I stress for 50 amps you need around 175 Amp Hours of battery capacity at the c/20 rate. or a whole bunch more at the Wal*mart rate (long story told elsewhere about how wal*mart cheats on their capacity ratings)

It's true that lower charge rates help in battery cycle life. Ideally many batteries want even less than C/3 for optimum charge rate for maximum cycle life, sometimes as low as C/10.

However, most GC-2 have a C/20 rate of 200+AH, not 110. the Trojan T105 is 225AH at C/20. so C/3 would be 75ish A charge rate.

Now a single smaller 12V, 75ish AH rating, yes be careful.

However, within reason charging at higher rates doesn't have a real dramatic effect on cycle life. And in the case of GC batteries, with 500-1000 cycles for cycle life, even charging them at C/2 doesn't seem to affect them much. Now in my case I hit the batteries at times with 120AH, which is C/2 except that I have 4 of them so it's really C/4. But I wouldn't want to try to hit a battery with a charge rate close to C unless they were designed for that high a charge rate. And if you have a single 12V battery and a 55A charger, well, be careful, but it probably wouldn't hold 55A for long.

[wa8yxm]

3 answers. one is a caution.

In the manual for my Prosine 2.0 Xantrex suggests a maximum charge rate of 30% the C/20 amp hour rate. so if you have say one pair of 110 amp hour GC-2 batteries in series (still 110 amp hours since in series you add voltage) that would be 33 amps max charge. Or less for most battery types. Or more for LIFELINE AGM only.

Second answer: If you have enough battery it will not HURT and no damage will happen but I stress for 50 amps you need around 175 Amp Hours of battery capacity at the c/20 rate. or a whole bunch more at the Wal*mart rate (long story told elsewhere about how wal*mart cheats on their capacity ratings)

Third answer.. MOST LIKELY OUTCOME. is only one device will charge the other will go into standby so you won't double charge rate.. That applies to "Smart chargers"

How parallel power sources work.

I see folks arguing that even in a parallel setup. such as I run, all batteries must be "identi9cal" which mine are NOT..

They give all sorts of myths as to why this is.
"The smaller battery will reach full charge and signal the converter to stop charging": True for batteries in SERIES, not in parallel.
"the smaller battery wi9ll "Draw down" the larger one.. No, not unless it shorts out.

NOTE even if they are all identical. Short out will draw down non shorted batteries.

Now with batteries in SERIES each battery in a single chain (usually 2 GC-2's) must be identical to its partner.. But adjecent pairs need not be.

Why is this that you7 can parallel different size batteries.
When discharging the battery with the higher voltage will provide all or nearly all, the power till the voltages match then each battery will prov9ide a share equal to the size rati9os. so if you had two batteries one 100 amp and one 50 one would provide 2/4 (the 100 amp) and the other 1/3 (the 50)

And charging. the battery with teh LOWER voltage will suck nearly all the power till it reaches the same voltage as the other then. See above.

Once equality (State of charge) is reached, they will remain in lock step. and when one readches full (or empty) the other is there as well.

Now with multiple CHARGERS. the onhe with the higher voltage (they are almost never exactly the same) will provide the lion's share of the charge, up to all of it, while the other one goofs off and does nothign.

[Sam_Spade]

ktmrfs wrote:

and there is no mickey mouse stuff, I just turn one or the other on or both on. both are connected to the same battery bank in parallel.

In this WHOLE discussion, did you miss the main point......which IS that connecting two chargers at once might not give you significantly more total charging current than just ONE.....because both may "adjust" for the presence of the other.

What actually happens depends on which two chargers you have.

[ktmrfs]

Dirtpig wrote:
I feel like it would be much less of a hassle to just upgrade your converter/charger to a 75amp/100amp model. No Mickey mousing clamping or disconnecting batts. Just my 2c.

well, since I have a 2000VA generator, it will NOT run a 75 or 100A charger. so, I have a 55A charger in place of the WFCO and a 65A in the pass through. when only on one generator, on goes the pass through 65A. when I have shore power or two generators then I crank them both on and get 110A or so for quite a while.

So, there are reasons to have two chargers rather than one.

and there is no mickey mouse stuff, I just turn one or the other on or both on. both are connected to the same battery bank in parallel.

[Dirtpig]

I feel like it would be much less of a hassle to just upgrade your converter/charger to a 75amp/100amp model. No Mickey mousing clamping or disconnecting batts. Just my 2c.

[Sam_Spade]

BFL13 wrote:

No idea where you are getting that idea from.

A bit off on a tangent......
A friend of mine has a charger similar to those pictured.
We checked the charging voltage and saw it go up as high as 17.5 volts. That seems a bit high to me.

On topic: My guess is that having identical chargers might increase your chances of success......might.

The idea comes from the fact that "smart" chargers adjust their output based on the "back voltage" or internal resistance it sees from the battery. If part of what it sees is NOT the battery but another device, the odds of things not working right are high.

[Ivylog]

Yes it will work.

[scrubjaysnest]

jbeliera wrote:
Here is a technical question. Let's say you want to charge your house batteries on your RV quicker. If you have two 12 volt batteries in your battery bank would you charge that battery bank quicker if you put two 25 amp battery charges on at the same time. Would that be possible to increase charging amps and less charge time or would it fry your batteries

We do this with a pair of smart chargers to reduce ginny run time. Once you reach about 80 or 90 % charge won't make a lot of difference.

[BFL13]

MrWizard wrote:
parallel 12v ?
yes..IF the batteries are low enough SOC
if they are taking everything charger #1 can produce, charger #2 might increase total amps into the batteries

this will increase the amps, but only until the amps drop below what the charger with highest voltage can produce, at that time the lesser charger is doing nothing

To clarify, the second charger is not then necessary, but both chargers could still be doing something. If one's voltage is not far below the other's and both are above the battery voltage, you can have say:

Battery acceptance 40 amps
Charger 1 (60 amper and a tad higher in voltage) and Charger 2 (20 amper) where you are seeing eg, 35 amps plus 5 amps for total of 40.

Charger 2 is still doing some of the amps and Charger 1 is not doing all it could. Yank Charger 2, and now Charger 1's amps jump from 35 to 40.

The amps each does is proportionate to the "spread" between their voltages and the battery voltage. It is not all or none. The lower voltage one will have its amps start to taper first but then you can have both with tapering amps. Two equal 40 ampers would be showing 20 and 20. Pull one and the other jumps from 20 to 40.

One thing to note, if you have a power interruption (gen pops a breaker eg) then to restart the whole thing, you must get the lower voltage charger running again before you start the other or you might not be able to get the lower one going. It can just indicate "full" if the higher voltage one is going.

[MrWizard]

parallel 12v ?
yes..IF the batteries are low enough SOC
if they are taking everything charger #1 can produce, charger #2 might increase total amps into the batteries

this will increase the amps, but only until the amps drop below what the charger with highest voltage can produce, at that time the lesser charger is doing nothing

[time2roll]

Fry the batteries? NO
Faster? YES, however only the first 15 minutes will be twice as fast. For two low batteries you might get them charged in 4 to 5 hours instead of 5 to 6.

Please post your results.

[ktmrfs]

I quite often use two PD chargers in parallel when I have enough power available One is a 55A, the other a 65?A. charging four GC. No issue, and I consistently get 110A into the bank for quite a while. and the charge doesn't seem to taper as fast as using one only. Now different chargers may yield different results.