PL 8 - Q and A section - How to Set up - Use etc,

[Burgerman]

I have not read anything on paper in years. Why would you do that when its online as a pdf file?

[Scooterman]

Reading stuff on WD.com and the forum was the reason I bought my kindle fire hd 10 on black Friday. I thought it'd be better than readng threads and pdfs on my laptop. But I don't like the kindle either, but it's okay for watching Netflix and catchup tv.

I'm much better with a paper copy and I thought printing off the PL8 Manual would be worth it. Although most of the manual is cell and battery connection diagrams. I wish there was much info on the CCS. Although the CCS on-screen explanations are very good.

I find it very interesting and would never go back to lead, at least not on my main item of mobility equipment (i.e. Scooter). Although I went out in the salsa today which was a nice change.

[Burgerman]

Me too since we are having a heatwave!

I have my modded salsa here, and a stock older one without the fat tyres, and seating options.

So I have mine,centre footplate, seat moved back, 10 inch casters and fat 120 wide rear tyres and its heavy because of me (20 stone) and all that seating gubbins.

And a neibours one that he wanted programming in my garage. With less weight, no seating options, nose heavy, and swing away footrests. And 3 inches of dust.

My carer is 5 stone lighter than me. In the stock chair he went on the lawn and instantly got stuck. Its smaller 9 inch overloaded casters sunk a little, and the too lightly loaded rear thin tyres just spin on the grass. My own chair, with a heavy seating system, and a fat user, and wider tyre/rearward seating worked fine on the grass. I ran rings around him... Few small changes make all the difference. Its one reason testing a typical stock chair tells you nothing useful.

[Scooterman]

I've got 9" castors on my salsa, but I did try a set on your heidenau 10 x 3 inch tyres, but they wouldn't fit my forks. But they are physically a lot bigger than the 1 inch difference would ordinarily lead you to think. So I can see how they're a big benefit for a heavier chair/user. I notice Shirley has adapted his forks to accommodate 10 x 3 castors.

But the 9" are fine on my chair as it's so lightweight for a powerchair and has a heavy rear/front weight bias.

I learnt from my days in a manual chair that too much weight up front leads to dangerous castor flutter at speed and especiallywhen going downhill

[Scooterman]

Back on topic...

What is the dc/dc converter frequency for?

[Burgerman]

Its not what its for, its how it works.

For e.g to get a 6V output from a 12V source you use a 50% on and 50% off high frequency square wave. The speed that the square wave happens is the frequency. For high currents and small cmponents you need high frequencies. But the higher the frequency the lower the efficiency ...

[LROBBINS]

A DC-DC converter isn't just a PWM switch (though that could, I guess, be used for a rather inefficient "buck" converter). A DC-DC converter is really a kind of switching power supply that uses an inductor to store energy. Series resistance drops voltage, but instead of it being wasted as heat this energy gets stored in the inductor. It then feeds it back as the voltage is going up again (to a voltage lower than input in a buck converter, higher than input in a boost converter). In general, the higher the frequency the smaller the inductor that can be used. DC-DC converters pretty typically have efficiencies near 90%. Compare that with a linear regulator, say for 12V to 5V. The linear regulator is wasting 7/12 = 58% of all the energy as heat, the converter is wasting just 10%.

The above just converts the voltage. Where PWM comes in is to regulate that voltage. The output is compared with a reference and the difference is used to vary the PWM duty cycle so that the output stays constant even with varying loads.

Of course designing an actual circuit is much more complex, and way beyond my knowledge level. If you're curious, however, here's a tutorial from Maxim: https://www.maximintegrated.com/en/app-notes/index.mvp/id/2031. I'll just continue to buy them, especially now that they are an order of magnitude less expensive than the first one I bought about 25 years ago.

[Burgerman]

I think he may be refering to the frequency option in the PL8. Which works exactly as you explained.

It offers 3 different frequencies that you can choose.
Because to keep costs and physical size down, while offering 40A of power at 1 to 35V out, it uses 3 user selectable frequencies.

At the lowest frequency, 31khz, the size of components such as capacitors and inductors would need to be increased for high Amps. So when charging at 40A the high frequency or mid frequency is used (depending on the max min allowed Amp setting in the preset) to allow high power with small components albeit at lower efficiency.

And the opposite is true, for small sub 3A max currents it lets you use lower frequencies as it improves efficiency and wastes less power.

So you have these 3 options:

[Scooterman]

Thank you both for the detailed replies

I sort of get it...

Before asking the question here (troubling you guys), I thought Google it. And in an RC forum someone said the PL8 will overrule your Hz selection of you select the wrong value.

So is a rule of thumb, for high current select high frequency? I shall have an experiment later with the PL8 to see what it allows me to select with various CCs.

[Burgerman]

If you try to charge with a preset that ALLOWS a wide current range to be set you will be forced to use the middle 62khz one. It can be used from .1A to 40A.

If its an under 2 or 3A max preset for small cells only, it will give an error if you choose anything but the 31khz...

If its a high power preset, and current is set high, you will be able to use either the middle one or the 125khz one...


Its at its most efficient at 31khz. And its least efficient at the 125khs setting. But those are allowed only on low and high current settings/presets.

[Scooterman]

If you try to charge with a preset that ALLOWS a wide current range to be set you will be forced to use the middle 62khz one. It can be used from .1A to 40A.

If its an under 2 or 3A max preset for small cells only, it will give an error if you choose anything but the 31khz...

If its a high power preset, and current is set high, you will be able to use either the middle one or the 125khz one...


Its at its most efficient at 31khz. And its least efficient at the 125khs setting. But those are allowed only on low and high current settings/presets.

I suppose we use a wide current range when charging lithium or charging lead via andersons, so I gues the 62kHz one is most suitable.
And 31khz for my tiny 600mah life cells

[Burgerman]

Correct.

[Scooterman]

[Scooterman]

If I run the CCS without being connected to the PL8, it always shows the Generic OEM presets, not our own custom presets.

And if I load one of our presets (http://www.wheelchairdriver.com/PL8v2-Presets/) into the CCS, when I do connect to the PL8 I can't write it to the PL8.

In fact the complete opposite happens. The presets stored in the PL8 are loaded into the CCS and overwrite any new CCS custom preset I may have added before I get a chance to write it to the PL8.

Unless I'm doing something wrong, it means there's no point in loading or modifying any presets in the CCS without being physically connected to the PL8. Unless of course you have done BM's Bluetooth mod.

[Burgerman]

Connect the PL8. Load the CCS program. Add the new preset or any changes you want. Then UPDATE the PL8.

[Scooterman]

Connect the PL8. Load the CCS program. Add the new preset or any changes you want. Then UPDATE the PL8.

Thanks I'll try that

[sin85]

Hi,
need help.
i am setting up 14 cell block of https://www.lifepo4-batteries.com/sale- ... f-car.html . I want to charge them as a monoblock via PL8. Anyone have a preset? I am using balancer for charging only (or rather 14 balance boards for each cell)

thanks

[Burgerman]

I read that 4 times. nd have absolutely no idea WHAT you are actually doing.

Why 14 cells? That will not do 24V or 36V or 48V. So presumably you are making a 3.2 x 14 pack?

A 14S battery?

You need to make up a loom, for 2x 7S packs bolted together as 1 battery right? And use 2x PL8 to charge it from 2x isolated power supplies?

If I guessed any of that wrong, please try and explain a little better!

I want to charge them as a monoblock via PL8.

PL8 can only do up to 8S.
You will need to connect a pair of charge cables, and balance connector and charge it twice, as 2x 7S batteries.
Or...
Have a means of disconnecting it in the centre and charging it as 1 big 7S battery in parallel.
Or...
Use 2x isolated power supplies, and 2x charge connections and charge as 2 halves wit 7 cells each, at the same time.

Which?

Anyone have a preset? I am using balancer for charging only (or rather 14 balance boards for each cell)

And this bit makes absolutely NO sense!

[sin85]

sorry i will be clearer

i am using bms for charging only;
yes i am building s14 pack as i am using single channel 300A roboteq. the pack gives me nominal 44.8V.
i want to charge my pack as if it is a single 44.8V battery

hope this clarifies things

[sin85]

and i have enough space for a single s14 pack

[shirley_hkg]

sorry i will be clearer


i want to charge my pack as if it is a single 44.8V battery

You need a 0--60V CC / CV power supply ; not PL8 .

[sin85]

hi Shirley

do you have any suggestions? make, model, price? how would I set it up?

[Burgerman]

Thats not actually true.
I charge a 45V 13S BM3 pack with a pair of PL8s...

[sin85]

do you have a preset?

[Burgerman]

I have one for 7S and one for 6S to make my 13...

http://www.wheelchairdriver.com/BM3-con ... arging.gif

I can do you one if you want for 7S and to charge and terminate correctly for a 200Ah pack? Is that what you are looking for?

To do this you will need to use 2 SEPERATE and ISOLATED power supplies. Or smoke!!!
To be sure they are isolated, test resistance between both power supplies NEGATIVE output connection while they are on. It should be super high. Like many thousands of Ohms.

Then you need to connect the 9 balance wires, and 2 power wires, to the first 7S block of cells as if it was a stand alone battery... And do the same with the 2nd block of 7 cells. Be sure you understand what you are doing or it will end in smoke!

If you grasp it, its perfectly safe.

Its why I have 2 PL8s connected together here as one. Each has a seperate power supply. You need 2 cables obviously.

http://www.wheelchairdriver.com/BM3-con ... DCABLE.jpg

I dont charge overnight. It charges so fast that I do it anytime during the day while sat at my computer. And if you dont find time its still ok because RANGE!

[sin85]

I was more thinking along the lines of treating my pack as 1S as I do not wish to utilise pl8' balancing function. On my current set up (Hyperion) I do not use balancing wires. I have bms for charging only. I have used that for the past seven years and my old cells still have 75% capacity when tested under load 2 months ago. I can continue to use Hyperion, however, it has, as you know, 100A charge limit and I have to turn it off and on again which is inconvenient when charging overnight.

[shirley_hkg]

To do this you will need to use 2 SEPERATE and ISOLATED power supplies. Or smoke!!!

Could they be powered from one supply ?

[shirley_hkg]

sorry i will be clearer


i want to charge my pack as if it is a single 44.8V battery

You need a 0--60V CC / CV power supply ; not PL8 .

This is no advertisement . Don't get me wrong .


viewtopic.php?f=2&t=7670

[Burgerman]

Only if you have a removable link that seperates both halves into 2 seperate packs.

Could they be powered from one supply ?

And if you do that then yes.

[shirley_hkg]

Oh , two batteries . I see.