Combining PSU Voltage

[xboxhaxorz]

I have a charger that is rated at 1000w 30a output with a 5 to 36v input
http://www.hobbyking.com/hobbyking/s...e_Charger.html

I have 2 brick style power supplies for a really old laptop that are rated at 20v 6 a and i have cut the end off and connected the 2 wires to the charger

In the charger it showed it using 16v with a max of 9 amps, so i am not sure how that came about

But i was looking to combine the 2 power supplies to provide more power to the charger, with the 20v rating that would be 4v over the input for the charger

Since the charger had displayed 16v that would be 32s which is fine for the power supply

Would be grateful for some information

[budm]

Re: Combining PSU Voltage

"I have a charger that is rated at 1000w 30a with a 5 to 360v input" as low as 5V input with 1000W output? That makes no sense at all, at 5V input the current will be 200A! if there is no conversion loss.
Can we see what you really have on this charger? Make, model, spec, pictures, etc.

[xboxhaxorz]

Re: Combining PSU Voltage

I have edited post and provided a link

[budm]

Re: Combining PSU Voltage

Well, it still does not make sense with 1000W 30A output. P = I .E, so what is is the output Voltage rating? 1000W @ 30A means the Voltage is around 33V.
So at 5V input I do not think you will get 1000W output, like I said the input current will be 200A @5V input, you are going to need on BIG FAT WIRES.
It is missing input current requirement.
1000W@input voltage 23V & 500W@input voltage12V
As you can see the capacity drops as the input Voltage goes down.
At 23V input for 1000W output, the input current will be 43A!
at 12V input @500W = about 42A inout.
so at 5V input, the power output will be around 200W (40A input current)
and that with 100% conversion which is not gonna happen.
So it looks like the input fuse must be around 45~50A range.
So to get the power you need at the output, the power supply feeding the input should be around 20% or more capacity than the output you need.
So tell me again what your laptop power supply can do, and it may go into shut down if the protection circuit is sensitive to high in-rush current.
"old laptop that are rated at 20v 6 a "
"In the charger it showed it using 16v with a max of 9 amps, so i am not sure how that came about" Did you actually check the DCV output to see if it actually drops down to 16V.
20V * 6A = 120W. 16V *9A = 144W much higher than the rating, something is not right and I do not expect the power will last.
And if you manage to get 32V at 9A, the power output will be only 288W but with the conversion loss it will not be that much. You should also use bigger wire to reduce the loss due to the small wires gauge.
BTW, putting two power supplies in series you have to make sure that the Negative is not tied to the AC SAFETY ground. I would get one big power supply instead.

[xboxhaxorz]

Re: Combining PSU Voltage

I understand that lower voltage wont provide the maximum watts, i was just supplying the information on the charger

So the 16v shown on the charger was actually the rate of the battery, its a new charger so i did not realize till i used the DMM

So i have 2 20v PSU , i cut the ends off the cables and was going to solder the wires together to connect to the charger

I wasnt sure if that was safe or would work and also because that would give me 40v, which is more than the 36v the charger can take

[ben7]

Re: Combining PSU Voltage

I understand that lower voltage wont provide the maximum watts, i was just supplying the information on the charger

I don't blame you, I read the specs and they were a little confusing at first. It seems to me that the charger has a dual direction DC-DC converter ... awesome! It can have power go either way, so there is no specific input or output.

Otherwise I'm not sure what to say about the power supplies (refer to them as power supplies, they aren't really chargers at all, and it is confusing to say you are powering a charger with chargers...lol).
Putting them in series results in too high of a voltage, and parallel ... well those probably aren't designed to be paralleled. If you are good/decent with electronics, you could modify the power supplies to output a slightly lower voltage, like 15V, and put them in series to get 30V. The output current rating of the power supplies doesn't change. However, I only suggest you do this IF you are good with electronics. The power supply is a shock hazard when taken apart (even when un-plugged!)!

[budm]

Re: Combining PSU Voltage

I only see DC-DC converter with red.black input wires and output ports, I do think it can be used in reversed (dual directions).

Input voltage range: 5.0~36.0VDC
Charging current range: 0.05~30.0A
Advance synchronous buck-boost DC/DC converter technology with an output conversion efficiency that can reach over 90%

"I wasnt sure if that was safe or would work and also because that would give me 40v, which is more than the 36v the charger can take"
Do you have user manual?

[momaka]

Re: Combining PSU Voltage

Looking at the limited information on that page, I am guessing this is a smart charger for all kinds of RC and hobby batteries, including Lithium.
I wouldn't worry too much about those stated wattages on the cover. They seem to be more of a marketing gimmick than anything.
And brush DC motor "break-in"?! -That is absolute marketing foolishness right there.

But anyways, let's get to brass tacks.
What you really need to know is what kind of battery pack your are charging (i.e. Lithium, Ni-MH, etc.), its voltage, its capacity, and how fast you want to charge it (without overheating it, of course).

Based on that, you will know how much power you need.

If you have just a typical 1/10th scale RC car battery back, and if you don't want to deal with all of these calculations, just use only one of those 20V, 6A laptop chargers, and use a slow charging profile for your batteries.

Assuming the laptop chargers you have can output 5A continuous without overheating or running hot, you can have
5A x 20V = 100W at the input of the charger.
Again, more ASSuming: if the charger has an efficiency of 80% (the 90% they give is not a minimum, so obviously it can be less than that), then you will be able to get only about 80W of output from the charger. If you know the battery pack voltage, then you know what is the maximum current that you can charge the batteries with (assuming the batteries can even take that charge current).

So for example, if you have a 10V battery pack, and you use the above laptop adapter and numbers I mentioned, then you will be able to charge the battery pack with a maximum of
80W / 10V = 8A of current.
But again, your battery pack better be capable of taking that current without overheating. Otherwise, you might run into some serious issues - especially with Lithium batteries.

Of course, if you want to charge the battery pack with less current then that, then this would be okay, since you will be drawing less power from the output of the charger, which in turn will draw less power from the laptop adapter. The only real problem can be the reverse of that - if you are trying to charge the batteries so fast that you draw too much power from the charger and the laptop adapter cannot take it.

[xboxhaxorz]

Re: Combining PSU Voltage

The pack i have is a 4s 6500 mah, which can be charged at 3 times its rate

The charger i have is more than enough for it, i just need a power supply for it

This is the power supply i have http://www.pchub.com/uph/laptop/46-2...er-Laptop.html even though it says 6a, it was charging the battery at 9a

[budm]

Re: Combining PSU Voltage

I doubt that it can really do 9A.

[goontron]

Re: Combining PSU Voltage

FYI, i have had luck combing different voltage PSUs for more current using large Diodes. you also want ceramic disk caps across the diodes and a filter cap (2200uF is what i used) on the output. not sure the efficiency, but if its anything like the diode bridge used in some server for PSU redundancy and hot swapping its not overly efficient.

[momaka]

Re: Combining PSU Voltage

I doubt that it can really do 9A.

Agreed.

Most of those adapters have current shunts and pretty well set over-current protections. If for whatever reason you really are able to pull 9A out of it, the adapter will either overheat or have a short life.

Like I mentioned in my post above, if you know the battery pack voltage, just divide 80 by the battery pack voltage and use this as the maximum available current with which you can charge the batteries.

Judging by the PC USB connection, I am going to assume that this "fancy" charger has various charge profiles you can use. So just use one that doesn't have its maximum current above the limit you find above (and of course one that doesn't charge the batteries so fast that it overheats them).