Battery bank for o2 concentrator

I am unable to get into my PM because I updated my email address and that deactivated my account and it can take days/a week or more to get it activated at this time.

CapnLoki - I would love to pick your brains about a battery bank for an O2 Concentrator. I am betting the notice I had a PM waiting is the response from you after I sent my last PM to you. I can't go see it as I updated my email and got deactivated and they are on the slow side activating people.

I also figure down the road others looking to run o2 concentrators on batteries can benefit from reading this.

I talked to engineers and got some wonderfully detailed information from them about running their smaller more portable O2 concentrators at 3 liters continuous.
I am thinking of putting the cpap on the regular RV house batteries since it will not use much (leaning strongly to the new dreamstation).

Two problems in using the O2 concentration off battery (not plugged into electricity):

1) The O2 concentrators quit working when the battery voltage drops below a certain point (eg. 10.5 or 11.4 volts, it varies across the units). And it doesn't work at peak performance (eg. 3 Liters continuous or that plus charging the battery at the same time). One of them self heals itself (nice feature), as it gets older it runs harder in order to deliver the correct level of O2 so it needs even more (that was the first engineer that brought up this issue but checking with the others, yup they have it also). As you know 12V batteries will drop too low. The engineers at two companies had worked with customers who could not run run the machines off a car battery, so they had real life knowledge, as well as their tests they had done.

We could do an 18V battery or 24V battery. I have read that you want the batteries to be very similar (mfg date, usage - eg. don't mix old and new, etc.) so am guessing that three 6v batteries would be better than a 12v and a 6v, or two 12V batteries. Does that sound right?

The o2 concentrator gets used from 8-12 hours a night (any time hubby is lying down and really relaxed he need to use the cpap and o2 concentrator, this covers naps, drifting half asleep, long nights to catchup on sleep, etc.). This means 100-120 ah a night. I would rather not run out or be forced to run the generator all of a sudden.
Then in order to only use 50% of the battery (typically don't want to run AGM/flood below that, right?), that looks like 200-250 ah batteries.
Yes, I get this is heavy weight and gonna be a big ouch on the wallet. But like you, we want to be off the grid enjoying nature.

AGM vs flooded batteries - We do have a storage bin right under the bed, with an outside door and could run a cord to the bed area (and plug the o2 concentrator into that cord).
But there about 1/2" thick piece of wood above that bin which the mattress sits on and there are a few holes in that (cords running thru) so if you lift up the thick mattress you could see into that bin. Even if we secured it well in that storage bin, I believed you were saying you would use AGM deep cell batteries close to a bed because of fumes occurring over time. Do you have an opinion of with a 1/2" piece of wood with a few smaller holes and a thick foam mattress would be enough of a barrier or better to use AGM?
I figure we will be using these batteries for a very long time so AGM might be fine to invest in.

Thanks for any info.

cpapwife (as guest since changing my email address left me unactivated) wrote:
...
1) The O2 concentrators quit working when the battery voltage drops below a certain point (eg. 10.5 or 11.4 volts, it varies across the units). And it doesn't work at peak performance (eg. 3 Liters continuous or that plus charging the battery at the same time). One of them self heals itself (nice feature), as it gets older it runs harder in order to deliver the correct level of O2 so it needs even more (that was the first engineer that brought up this issue but checking with the others, yup they have it also). As you know 12V batteries will drop too low. The engineers at two companies had worked with customers who could not run run the machines off a car battery, so they had real life knowledge, as well as their tests they had done.

We could do an 18V battery or 24V battery. I have read that you want the batteries to be very similar (mfg date, usage - eg. don't mix old and new, etc.) so am guessing that three 6v batteries would be better than a 12v and a 6v, or two 12V batteries. Does that sound right?

I'd have to give this more thought - an 18V system creates a lot of issues. 24V is more feasible, but it only works if the concentrator works better on 24V than 12V, or maybe accepts any voltage from 11.5 to 24.

But my first thought is that if the load drops below 11.5, then the battery bank is just too small (or not fully charged). I can drive my bank (4 6V batteries, for 480 Amp hours at 12V) that low by running a microwave, but that's a 90 Amp load! Since we only run this for a few minutes, its not a big deal, although for those minutes the whole system is affected. Your system will be a continuous load, so the voltage drop can be read as a "state of charge" meter. (Its not linear, but close.) In other words, you should just size the bank big enough to handle the load. By having a separate bank, you don't have to worry about other load suddenly dropping the voltage.

There will be a new problem - coming up with 100 amp-hours a day is a serious nut! I used to have a deep freeze that needed that - I ended up throwing it all away! But this is another discussion.

cpapwife (as guest since changing my email address left me unactivated) wrote:
... This means 100-120 ah a night. I would rather not run out or be forced to run the generator all of a sudden.
Then in order to only use 50% of the battery (typically don't want to run AGM/flood below that, right?), that looks like 200-250 ah batteries.

Two large deep cycles - my quality Trojan T125 flooded batteries are 240 AH at 6 volts, so two in series are 240 AH at 12 volts. Cost about $350. The best choice will depend on the space. If you think you might need "just a bit more" do two 12V batteries in parallel so you can add a third.

cpapwife (as guest since changing my email address left me unactivated) wrote:
AGM vs flooded batteries - We do have a storage bin right under the bed, with an outside door and could run a cord to the bed area (and plug the o2 concentrator into that cord).
But there about 1/2" thick piece of wood above that bin which the mattress sits on and there are a few holes in that (cords running thru) so if you lift up the thick mattress you could see into that bin. Even if we secured it well in that storage bin, I believed you were saying you would use AGM deep cell batteries close to a bed because of fumes occurring over time. Do you have an opinion of with a 1/2" piece of wood with a few smaller holes and a thick foam mattress would be enough of a barrier or better to use AGM?
I figure we will be using these batteries for a very long time so AGM might be fine to invest in.

Fumes (primarily hydrogen but other noxious fumes) are caused by over charging. Lots of boats have flooded batteries in areas open to people, but are generally setup to vent overboard while engines are running. However you do it, there must be an easy path for H2 to get out. The other issue is the fumes imply water is lost and must be added, so the batteries must be easily accessible for inspection. If you would keep the batteries when you trade up AGM might be the best answer. AGM will still vent in extreme cases, but not in normal use.

CapnLoki wrote: I'd have to give this more thought - an 18V system creates a lot of issues. 24V is more feasible, but it only works if the concentrator works better on 24V than 12V, or maybe accepts any voltage from 11.5 to 24.

But my first thought is that if the load drops below 11.5, then the battery bank is just too small (or not fully charged). I can drive my bank (4 6V batteries, for 480 Amp hours at 12V) that low by running a microwave, but that's a 90 Amp load! Since we only run this for a few minutes, its not a big deal, although for those minutes the whole system is affected. Your system will be a continuous load, so the voltage drop can be read as a "state of charge" meter. (Its not linear, but close.) In other words, you should just size the bank big enough to handle the load. By having a separate bank, you don't have to worry about other load suddenly dropping the voltage.

That is good news, gives me hope.

The actual specs from engineers:
Oxlife brand o2 concepts (I think that is the model) were the first ones that brought it up. They said it would not run with 3 L continous while charging the battery (in the unit) off a car battery.
Deep cycle AGM 12v may be better at producing the voltage than a starting battery (typical car battery). I would believe this but do not know it for sure.
Their unit runs on 14.4 volts. They need 12 volt to run well. Below 11.5 they won’t run at peak use (3L plus charging). Below 10.5 it turns itself off to protect circuitry.

Igo portable engineer said 13.6 goes into the power brick. They said a running car battery goes from 13.6 to 14.4 volts. I have an outstanding question from them as to when it will no longer run at 3L (my first call was about AH usage).

Sequel engineers said their machines (eclipse & equinox) both run at 11.5-16V DC. They have seen issues running on a 12V battery (car & RV) when running at the higher flow (3L / min) and charging the o2 concentrator battery at the same time.
Below 11.5 the machines shut down.

Respironics only go up to 2 L/min so they are not at our top choice.
Innogen at home doesn’t even do DC (in any form) so they were crossed off our list.
I found no other units that went up to 3 L/min continous.

Some units have separate battery charging stations for the O2 concentrator’s batteries and that might work, to charge the o2 concentrator battery when the unit is not being used, but if the battery is charged full up (only gets used when the batteries I set up are not giving juice) that might not make a difference.

Maybe having a newer o2 concentrator at all times (eg. 3-5 years old not 10 years old) so it works better with 12v dc and picking a unit that desires something closer to 12v rather than 14v (eg oxlife). I am not familiar with oxlife as a company but found one DME (private pay that had very high ratings) that carried it said they have found it to be a very robust machine.

Thanks for your thoughts on all this.