Will two chargers charge two Freedom CPAP batteries faster than one charger?

If I have two Freedom CPAP batteries, I can charge them in the configuration in the pic below:


But if I get a second Freedom charger, would this be faster, or does it not matter?

Thanks!

mileena wrote: ↑

Thu Aug 09, 2018 11:18 pm

If I have two Freedom CPAP batteries, I can charge them in the configuration in the pic below:


fredom charge two batteries.jpg


But if I get a second Freedom charger, would this be faster, or does it not matter?

Thanks!

It might go faster, it all depends on how fast the battery will accept a charge, and how much current the charger can put out.

I don't have that data.

However, you can find out for yourself. Run the batteries down, charge a single one, time how long it takes to charge.

Run it down, then charge both batteries at the same time, and see how long it takes to charge.

OK, my electrical knowledge is pretty weak, but here's my go at it:

The batteries are 8 amp hours at 12VDC and take 4 hours to charge each. So with perfect efficiency it would be 2 amps each for 4 hours to charge, or 4 amps total. Even with only 80% efficiency the 6.75 amp power supply should be enough to charge both batteries in the rated 4 hour charge time. (I don't know if the batteries actually charge an an even current draw during the charging cycle, though.)

I'd email the manufacturer if you need a better answer. Or someone who actually knows electrical engineering can answer and correct me if I've made some errors. My guess is that it wouldn't make much difference if any. If it did they'd try to make more money and sell you two chargers.

Edit:
Palerider's empirical test sounds like a sound idea. No math needed, just results.

palerider wrote: ↑

Thu Aug 09, 2018 11:22 pm

mileena wrote: ↑

Thu Aug 09, 2018 11:18 pm

If I have two Freedom CPAP batteries, I can charge them in the configuration in the pic below:


fredom charge two batteries.jpg


But if I get a second Freedom charger, would this be faster, or does it not matter?

Thanks!

It might go faster, it all depends on how fast the battery will accept a charge, and how much current the charger can put out.

I don't have that data.

However, you can find out for yourself. Run the batteries down, charge a single one, time how long it takes to charge.

Run it down, then charge both batteries at the same time, and see how long it takes to charge.

Thanks palerider!

Here is the problem to your suggested solution:

I haven't bought the second battery yet. The second battery by itself cost $200. But the Freedom starter kit that I have now not only has the battery, but also the charger, splitter cord, DC socket cord, and some various pin adapters. That costs $249 at SleepDirect.com. If I were to buy the charger and second battery separately, it would cost $249 as well.

So if all I need is one charger, I will just buy the stand-alone battery for $200. But if a second charger is indeed faster, then I would by another starter kit, since it not only has the battery and charger, but the additional cables that I may or may not need, like the splitter cord. So I would get more for the same price than buying the second battery and charger separately.

So how I proceed in my purchase depends on if two batteries charge faster with two chargers.

Stom wrote: ↑

Thu Aug 09, 2018 11:41 pm

OK, my electrical knowledge is pretty weak, but here's my go at it:

The batteries are 8 amp hours at 12VDC and take 4 hours to charge each. So with perfect efficiency it would be 2 amps each for 4 hours to charge, or 4 amps total. Even with only 80% efficiency a 6.75 amp power supply should be enough to charge both batteries in the rated 4 hour charge time. (I don't know if the batteries actually charge an an even current draw during the charging cycle, though.)

I'd email the manufacturer if you need a better answer. Or someone who actually knows electrical engineering can answer and correct me if I've made some errors. My guess is that it wouldn't make much difference if any. If it did they'd try to make more money and sell you two chargers.

Edit:
Palerider's empirical test sounds like a sound idea. No math needed, just results.

Thank you Stom! You know much more than I do about electrical engineering.

I have no reason to doubt you are correct. You probably have saved me some money. But I will call the manufacturer tomorrow to see what they say!

Hi

I have two Freedom batteries and 1 charger with a pigtail splitter. I checked the voltage with a multimeter without the splitter, and it showed 13.55 v. I added the splitter cable and it again showed 13.55 v. I then plugged one of the cords into the dc in on the battery, and checked the voltage on the other cable and it showed 13.4 v.

Since the voltage dropped, I'm assuming it would take it a little longer but I cannot tell you how much longer.

-Bill

mileena wrote: ↑

Thu Aug 09, 2018 11:18 pm

If I have two Freedom CPAP batteries, I can charge them in the configuration in the pic below:
...
But if I get a second Freedom charger, would this be faster, or does it not matter?

So, the short answer is: There's probably not a lot of difference - it's a pretty bg charger that looks like it was spec'd for two batteries.

However, it really impossible for us to guess because while the charging specs for a lead acid battery are pretty standard, Lithium cells can be designed to a wide of variety of parameters such as fast charge, high discharge, long shelf life, many cycles, etc. The designer of a pack gets to choose what's important for their application. Because of this type of variability, we can only make a random guess at how fast a Lithium pack will accept a charge.

That said, the 6.75 Amp charger is pretty large so I don't see a problem except if the two packs are well discharged. In that case, the acceptance rate of the packs may exceed the charger for a brief period. Once the packs collect a partial charge their acceptance probably drops below the charger's output. So its possible that it takes 10 or 15 minutes longer to charge, but that's probably not worth spending $50 for another charger and the hassle involved. It also possible that the packs limit their charge rate to half the charger's output simply for heat dissipation reasons so there might be no difference at all. Only experimentation (or a call to the vendor) will tell.

A curious question is whether its advisable to always use the batteries together, so they act as one pack. That's certainly advised on lead-acid batteries, and mine stay bolted together for their entire life. Lithium cells actually have bigger issues with battery balancing and always have a "Battery Management System" to assist. So I'm no sure how well this works if the too packs often used separately and have different wear profiles. I'd be tempted to tape the two packs together and treat them as one battery.

wm_hess wrote: ↑

Fri Aug 10, 2018 4:56 am

Hi

I have two Freedom batteries and 1 charger with a pigtail splitter. I checked the voltage with a multimeter without the splitter, and it showed 13.55 v. I added the splitter cable and it again showed 13.55 v. I then plugged one of the cords into the dc in on the battery, and checked the voltage on the other cable and it showed 13.4 v.

Since the voltage dropped, I'm assuming it would take it a little longer but I cannot tell you how much longer.

-Bill

Thanks for your input Bill. I don't know much about multimeters, but at least I have a better idea now.

CapnLoki wrote: ↑

Fri Aug 10, 2018 7:45 am

mileena wrote: ↑

Thu Aug 09, 2018 11:18 pm

If I have two Freedom CPAP batteries, I can charge them in the configuration in the pic below:
...
But if I get a second Freedom charger, would this be faster, or does it not matter?

So, the short answer is: There's probably not a lot of difference - it's a pretty bg charger that looks like it was spec'd for two batteries.

However, it really impossible for us to guess because while the charging specs for a lead acid battery are pretty standard, Lithium cells can be designed to a wide of variety of parameters such as fast charge, high discharge, long shelf life, many cycles, etc. The designer of a pack gets to choose what's important for their application. Because of this type of variability, we can only make a random guess at how fast a Lithium pack will accept a charge.

That said, the 6.75 Amp charger is pretty large so I don't see a problem except if the two packs are well discharged. In that case, the acceptance rate of the packs may exceed the charger for a brief period. Once the packs collect a partial charge their acceptance probably drops below the charger's output. So its possible that it takes 10 or 15 minutes longer to charge, but that's probably not worth spending $50 for another charger and the hassle involved. It also possible that the packs limit their charge rate to half the charger's output simply for heat dissipation reasons so there might be no difference at all. Only experimentation (or a call to the vendor) will tell.

A curious question is whether its advisable to always use the batteries together, so they act as one pack. That's certainly advised on lead-acid batteries, and mine stay bolted together for their entire life. Lithium cells actually have bigger issues with battery balancing and always have a "Battery Management System" to assist. So I'm no sure how well this works if the too packs often used separately and have different wear profiles. I'd be tempted to tape the two packs together and treat them as one battery.

That's a good point about heat dissipation. Maybe there is a limit. I will have to call them today to see if they know.

I never thought of your two-battery-as-a-pack question. The thing is, they both also have a USB outlet as well, so you would have to charge to identical phones or whatever at the same time to drain them equally, which is not going to happen. I bought one battery, and plan to test it out for the next three nights, as soon as my DC cord adapter comes in the mail. If I like it, I will buy another battery and use them as a pack. This will last me 2-4 nights without heated humidification and heated hose, or 1-2 nights with them. My pressure is higher though than the 10 cm H20 they test it at (I use 13-15 cm H20 on my DreamStation APAP). They also recommend turning off the Cflex to increase battery life, which I don't know if I want to do (mine is set at 2 now).

I will try not to use the USB port since this is an expensive way just to charge a phone. I will reserve the batteries only for my CPAP machine since they have a limited life (up to 500 charge cycles). Hopefully, if one battery has 3 more days usage on it than the other after testing it, it won't matter too much. I also think the two battery issue would be an ongoing problem for them, since I would assume many users add a second battery well after the first has been used, for whatever reason: financial, first battery is getting low, they didn't realize they could use two, etc.

The other issue I noticed is the new battery first said 99% out of the box, then 90% while charging, then 99% when I unplugged plugged it from the charger last night after 30 minutes or so. I didn't use it at all last night, and now this morning it says 95%. Wild fluctuations. I will ask them about this when I call today.

UPDATE:

I just called Battery Power Solutions, who makes the Freedom battery (btw, they have great customer service--they picked up on the first ring and the rep knew the answers to all my technical questions; he was very knowledgeable). This is what I learned:

1. To answer CapnLoki's question:

It does not matter if I use two batteries together and one happens to be older. One might take longer to charge, but there will be no difference!

2. If I use two chargers instead of just one charger with a pigtail splitter cord to charge two batteries, it will save me two hours.

3. All the fluctuations I am seeing for the battery charge is normal for a new battery. It will resolve itself in a few cycles. I can reset the circuit board and display screen if I want (he told me how).

4. An increased pressure of 13-15 cm H20 that I use will not be that much more of a drain on the battery than their tested 10 cm H20. Also, my Cflex will not drain it much more, nor will a leak in the mask. However, if I use a bilevel machine, where the pressure is continually varying, that will drain the battery much more. But a non-bilevel APAP or Cflex is fine.

5. The special Respironics DreamStation adapter cord, which costs around $70, is better to use than the DC Respironics DreamStaion shielded cord (about $25-$30) with the adapter they included in my starter pack. This is the $70 special adapter cord:




This is the cheaper Respironics DreamStation sheilded DC cord I bought for under $25:



The reason the former cord is better is that in low voltage situations (where the battery is more drained, like lower than 50%?), the cord is designed to use the full capacity of the battery, whereas the cheaper Respironics DreamStation shielded cord may (or will?) not be able to tap in and suck all the juice out of the battery, so I may not get the full capacity.

mileena wrote: ↑

Fri Aug 10, 2018 1:00 pm

The reason the former cord is better is that in low voltage situations (where the battery is more drained, like lower than 50%?), the cord is designed to use the full capacity of the battery, whereas the cheaper Respironics DreamStation shielded cord may (or will?) not be able to tap in and suck all the juice out of the battery, so I may not get the full capacity.

Not that anyone cares, but the bad news is if I choose to return the shielded DC cord for Respironics DreamStation that is supposed to arrive today for the better cord, I will have to pay a 15% restocking fee and pay for return shipping all the way across the country. This will leave me with a refund of only $8-$13 out of the original $23.75 I paid, depending on how big the 1.2 lb. package is that I have to return (i.e., does it fit in a USPS flat-rate box?). For that amount, I might as well keep the cord or sell it on eBay or wherever.

I am angry all these CPAP companies are allowed to sell these DC DreamStation shielded cords and claim that is the solution when they are not capable of using the full battery. The DreamStation actually requires a special cord that matches its proprietary voltage system. Other cords can't read when a battery is low voltage and the machine shuts off.

So now, I have to wait even longer and order this special cord, when I was supposed to test out my new Freedom battery tonight. I can still test the cheaper cord (which comes today in the mail) with my new battery, but it won't be a good test since all the battery won't be drained and I won't know how long the battery truly lasts for me.

Do I have a case for false advertising for this item I bought:

https://www.directhomemedical.com/11207 ... cpap.html



I want to return it, but think it is not fair I have to pay a restocking fee and shipping. I want this cord instead which is meant for getting all the juice from low voltage batteries:

http://www.batterypowersolutions.net/pr ... r-adapter

mileena wrote: ↑

Fri Aug 10, 2018 1:45 pm

Do I have a case for false advertising for this item I bought:

No. You bought the *respironics* 12 volt cord. There's nothing wrong with it.

palerider wrote: ↑

Fri Aug 10, 2018 2:57 pm

mileena wrote: ↑

Fri Aug 10, 2018 1:45 pm

Do I have a case for false advertising for this item I bought:

No. You bought the *respironics* 12 cord. There's nothing wrong with it.

Ok, thank you. I just know the DreamStation requires a proprietary voltage signal to use the full battery charge, which these shielded cords do not have. I think there should be a disclaimer about this product on the advertising.