Series 12v Chargers ?

[BFL13]

Bestconverter ad says,

"The PD9100L Series can be wired in parallel to charge at much higher current rates. They can also be wired in series/parallel to charge 36, 48, 60, 72 and higher voltage battery packs at high charge rates"

I keep thinking about going 24v battery bank. I have several 12v converters (PowerMax brand) Reading the above, I am wondering how that would actually work.

Say I put my adjustable 100 amper and my adjustable 55 amper in series to make a 24v charger. I would want the voltage to be 2 x 14.8, so I would set 14.8 on each.

How many amps would that make to the battery bank? I am thinking 55 where you get the lowest amps (like with solar panels in series?) but that 55 with 24v is like 110 amps with 12v, so that is not too bad?

Is that how it works? Or what? Thanks.

[CA_Traveler]

BFL13 wrote:
PT says the 100 will be doing 55 amps same as the 55 amper is. (But you don't add the amps)

If in fact the 100 is adding its voltage, but no amps, what would its draw on the generator be?

55*29.6 plus about 15 percent for losses for bulk charging.

That is IF the 55A charger will actually supply 55A.

[BFL13]

westend wrote:
Before you start any 24 V experimentation with your charging devices, I'd suggest you contact the mfg of these chargers and find out how they will react to having another power source in a series connection. Some devices don't have enough output isolation to try this and you could burn up a charger or all of them trying this out.

See figure 3 down here--I think that applies?

http://powermaxconverters.com/bowfishing-gear/

[2oldman]

BFL13 wrote:
If in fact the 100 is adding its voltage, but no amps, what would its draw on the generator be?

I'd have to say (55 x 12) watts.

[BFL13]

2oldman wrote:

BFL13 wrote:
I am having a hard time seeing how the 55 is doing 55 and the total output is 55, so why is the 100 doing anything?

The 100 is adding 12v of pressure, but no volume. An increase in pressure (voltage) or volume (amps) raises the wattage.

PT says the 100 will be doing 55 amps same as the 55 amper is. (But you don't add the amps)

If in fact the 100 is adding its voltage, but no amps, what would its draw on the generator be?

[westend]

Before you start any 24 V experimentation with your charging devices, I'd suggest you contact the mfg of these chargers and find out how they will react to having another power source in a series connection. Some devices don't have enough output isolation to try this and you could burn up a charger or all of them trying this out.

[2oldman]

BFL13 wrote:
I am having a hard time seeing how the 55 is doing 55 and the total output is 55, so why is the 100 doing anything?

The 100 is adding 12v of pressure, but no volume. An increase in pressure (voltage) or volume (amps) raises the wattage.

[BFL13]

2oldman wrote:

BFL13 wrote:
can you explain how come the 100 would do that a bit? .

The 100 can't push 100a through the small 'pipe' of the 55. PT's analogy is a good one.

For me it helps to think of a series of water pumps. Each increases the pressure, but volume is restricted by pipe diameter. Freeway traffic is another good analogy.

I am having a hard time seeing how the 55 is doing 55 and the total output is 55, so why is the 100 doing anything? I know you don't add the amps in series, but why aren't they sharing the 55 in some proportion say 20/35 ?

[2oldman]

BFL13 wrote:
can you explain how come the 100 would do that a bit? .

The 100 can't push 100a through the small 'pipe' of the 55. PT's analogy is a good one.

For me it helps to think of a series of water pumps. Each increases the pressure, but volume is restricted by pipe diameter. Freeway traffic is another good analogy.

[BFL13]

pianotuna wrote:
BFL13,

If you attach a 1/4" hose to a 6" pipe in series, the flow will be limited to what the 1/4" line can carry.

In your example, the 100 amp charger would only be doing 55 amps, while the 55 amp would be running flat out.

PT can you explain how come the 100 would do that a bit? I can't compare it with solar strings and blocking diodes etc, got lost.
---------

Then I should be able to swap the 55 for a 75 and now they each do 75. But that would have to be confirmed by VA count.

With the 100 only doing 75 it won't draw as much VA as when at 100, so the Honda 3000 should be able to run the 75 and the 100 in series, while it can't when they are in parallel doing 75 and 100.

It can only run the 55 and 100 in parallel. (The 100 is PF corrected but the 75 and 55 are not) The Honda cannot run the 75 and 55 in parallel--too much VA.

75 is way better than 55. 75 on 24 is like 150 on 12. So I could charge either way--55 and 100 in parallel on 12v or 75 and 100 on 24v and it would be the same recharge time. (155 vs 150)

[pianotuna]

BFL13,

If you attach a 1/4" hose to a 6" pipe in series, the flow will be limited to what the 1/4" line can carry.

In your example, the 100 amp charger would only be doing 55 amps, while the 55 amp would be running flat out.

[Naio]

DrewE wrote:
you would get faster charging by rewiring the batteries in parallel and operating the two converters in parallel

Most of this discussion is over my head, but in case it is useful I will mention that you probably don't have to rewire to do this.

I have 2x12v gel cells running the 24v motor on my ice machine, and I have hooked them up to 2x12v chargers, one charger on each battery, a few hundred times over the past 10 years, without disconnecting the batteries from each other. Batteries are still perky.

When using non-identical chargers, I do swap which charger goes on which battery.

Ok, back to regularly scheduled :B

[BFL13]

So if the output of the 55 and 100 in series is 55 is the 55 amper doing it all? The 100 amper just makes up the voltage but no amps? So how can it be running at any power? Or where do its amps go?

If the two are the same amps (as is "proper") why not each does half (of the half)?

[MrWizard]

If they were both 75 ampers at double the voltage then at the same full power, output would be 75 amps--37.5 amps each?

NO

it would be 75 amps at 28.8v etc..
provided the 24v bank could accept 75amps

just like solar panels, current stays the same as the smallest 'supplier' can pass, the voltage is double

75*28, not 37.5 * 28

if (2) batteries can accept 50amps each in parallel AKA 100*12, 50*12*2=1200w,
then they will accept 50amps in series
50*24=1200w

the charging configuration becomes very much like solar panels
you need chargers that have matching operating stats
same voltage and same current

i would not stack two different converters in series, except in a 'make do' situation, using needing higher voltage and LOWER amps

if changing systems, then start over with matching converters
designed for the job

[BFL13]

camperguy99 wrote:
I think we have overlooked a problem with the 55 amp unit. When the current gets near 55 amps it will go into current limit and "fold back the voltage" as the the current will decrease. For example look at the VI curves for the unpopular WFCO9855. I suspect others are similar. I have not been successful trying to parallel my 100 amp Magnum and a WFCO9855. No joy yet!

Nope. The 55 amper starts off at 55 amps and stays there till the batts get to near the set voltage of the converter (14.8) So all during bulk, whether 24v or 12v bank that is no problem.

You should be able to parallel the Magnum with the 14.4v WFCO by setting the Magnum to 14.4v. However, if the WFCO will not do 14.4, but only the 13.6, that is another added problem.

Yes I have a bunch of converters over the years. Two 100s, a 75, and a 55, (all PowerMax) Plus a 7355 and a 7445 (Parallax) Long story! Never mind. (Also three different solar controllers--never mind that either 🙂 )

I need a New Year's garage sale!

[DrewE]

BFL13 wrote:

These are single constant voltage but adjustable voltage chargers, so I can make them both 14.8 (or anything else in their pot range (12-15.5v)

I am still amazed at the idea here. Right now I can get 155 amps on my 12v bank with the 55 and 100 ampers in parallel. But that maxes out the Honda 3000. If I can run the 75 and 100 on the 24v bank (same batts re-wired) with the Honda, that is 75 on the 24v bank, same as 150 on the 12v bank? Wow!

That is not slower/longer, so I am still suspicious. 🙂

With a 24v bank I could run the 24v solar panel with a cheapo 12/24 PWM controller instead of the more expensive MPPT. (Tested that--gets equal or better results--see posts from two years ago or whenever that was)

Would still need a 24v inverter and a 24-12 converter (or put the rig's 12v converter on the 24v inverter.) The big 24v volt inverter is the killer for money, I think.

How did your 55A in parallel become a 75A in series? Or do you have three converters in question here?

But yes, half the current at double the voltage is the same power, and hence the same degree of overall battery charging (and the same generator loading). There's no magic involved. It's no different than an air compressor that may be switched between, say, 17A at 120V or 8.5A at 240V; the motor produces the same power and the air gets compressed at the same rate and your electric meter spins around and around the same amount regardless.

Frankly, I don't see any real advantages here to the 24V setup, and a lot of needless work and futzing and diddling your RV's electrical system and replacing 12V components with 24V components (or adding a DC-DC converter to run them). If you enjoy tinkering and fiddling about in its own right, then of course feel free to tinker and fiddle away.