My back up power set up questions UPDATE

[archangle]

Sleep_quest, I think AA answered most of your questions so I would like to address the 2nd AA who appears to have contradicted himself.

I would not attempt to charge a Jump Starter using the Jump Starter Cables. First, the Jump starter cables are not designed to work that way, they are set up to provide a large immediate amp output to Start Cars, not charge its own internal Batteries. I would suspect that the electronics actually are set up to prevent rapid charging in this manner.

The jump starter will provide a far larger current when jumping a car than it would to (connected the very same way) charge (with car already running) from the car to the jumper. So they are more than capable of handling any charge current.

I see three risks of connecting the jumper battery via jumper cables to another battery.

1) Too rapid charge. If the other battery has a full charge and the jumper battery is run down, it might provide too high a current into the jumper battery. While the jumper battery is designed to provide a high current for a short time, it might overheat if you hook it up to a larger battery that can provide a really heavy current for a long time. It might not be able to dissipate the large amount of heat generated quickly enough.

2) Too high or low of a voltage. The standard lead acid battery may not have the right voltage to charge the jumper battery. I think the voltage on a "resting" lead acid battery may not be the right voltage to fully charge the gel cell. The likely result is to not put a good charge on the jumper.

Both of the above don't worry me too much.

3) Shorted cell in the jumper battery. Sometimes when a jumper battery dies, it will die with one of the cells shorted. You now have a 10V battery instead of a 12V battery. The car battery might deliver a really high current into this partially shorted battery and cause a fire or other damage. Charging circuits are usually designed to limit charging current. You don't have this limit with a direct battery to battery connection.

[Guest]

Charging circuits are usually designed to limit charging current. You don't have this limit with a direct battery to battery connection.

You do in fact have the charging circuit of the car you are connected to.

You, my friend, have made a career of playing the devils advocate and talking in circles thoroughly confusing the people of cpaptalk.

[CapnLoki]

Did you not read what was posted?

Sorry Guest, who ever you are. You entirely missed the point. I have no trouble with using the Duracell as it was intended, simply plugging the Respironics "cigarette lighter" cable into the socket. I'm not a big fan of such "all-in-one" gadgets designed to a low price point, but I understand the need. Personally I prefer to use higher quality components that I can re-purpose as needs change. But I digress.

The problem in the original post was when Sleep_quest started talking about using a second battery with battery clips or using the jumper cables to connect to the Duracell. This completely defeats the safety aspects of the Duracell. The paradox here is the the whole reason to "solder, weld, wire, or otherwise construct" a back up power solution is to avoid the unsafe practice of using jumper cables and other such naked clips.

Stop it already STOP. The cables that come with the Duracell are no danger STOP to burning the house down. You are simply an alarmist. Stop it already.

I find it quite reprehensible that you would say this. This port supplies 50 Amps which is easily enough to spark and cause a fire, especially since we're talking about unsecured connections, intended specifically for use while sleeping in a bedroom environment. Think 600 Watt space heater with the cover taken off - that's exactly what you'd have if a cat knocked over a metal object in the middle of the night. Worse, the second battery used with just clips has naked posts that would try to instantly dump their entire charge through any metal object that happens to touch the terminals. Its obvious you've never seen this happen - it makes a big impression when a screwdriver turns red hot in a few seconds! There is a reason we always recommend a battery box or at least terminal covers, plus a solid connection.

Building such a box is really simpler than many of the posts make it out to be. The only issue is connecting to the battery, since each battery will have it's own style of terminal. Once you deal with that, there are wiring harnesses available that complete the job with appropriate fuses and socket. The "Battery Tender" charger I've mentioned comes with most, if not all, of what you need. Add a $5 box and you're good to go. For smaller batteries you can get by with slide on clips if they're insulated and the terminals are protected,

[CapnLoki]

I see three risks of connecting the jumper battery via jumper cables to another battery.

1) Too rapid charge. If the other battery has a full charge and the jumper battery is run down, it might provide too high a current into the jumper battery. While the jumper battery is designed to provide a high current for a short time, it might overheat if you hook it up to a larger battery that can provide a really heavy current for a long time. It might not be able to dissipate the large amount of heat generated quickly enough.

2) Too high or low of a voltage. The standard lead acid battery may not have the right voltage to charge the jumper battery. I think the voltage on a "resting" lead acid battery may not be the right voltage to fully charge the gel cell. The likely result is to not put a good charge on the jumper.

Both of the above don't worry me too much.

3) Shorted cell in the jumper battery. Sometimes when a jumper battery dies, it will die with one of the cells shorted. You now have a 10V battery instead of a 12V battery. The car battery might deliver a really high current into this partially shorted battery and cause a fire or other damage. Charging circuits are usually designed to limit charging current. You don't have this limit with a direct battery to battery connection.

All your points are correct to a degree, but the real problem is that you can't charge a 12V from another 12V. There will be a small current flow as the batteries adjust their charge, but nothing is really gained. As you point out there is the risk that a dead cell in one battery will kill the other, though this is not common with AGMs. In general, batteries should only be "banked" together if they are the same type, and ideally the same size and age.

[Guest]

And the 3rd alarmist rings in...

Sorry Guest, who ever you are. You entirely missed the point.

You mean after you entirely missed the OPs point, I missed yours? I thought your point was to confuse the OP? I got it.

The problem in the original post was when Sleep_quest started talking about using a second battery with battery clips or using the jumper cables to connect to the Duracell. This completely defeats the safety aspects of the Duracell.

The cables are designed to be connected this way and to deliver much more current than will be handled when re-charging this way or powering the equipment (5-8 amps DC). The cables will handle starting current in the neighborhood of 300 Amps DC. Quite the margin of safety there.

A box is a good idea and can be added at a later point when the poster is comfortable with the setup. They are not likely to find a box for $5 tho.

Did you know that you can die at home from a fall down the stairs if you get out of bed?

Did you know you can be killed by a BIG truck when driving down the road?
I have seen a BIG truck broadside a small car - nothing I could do. So now I sit home and warn people not to go out (from my bed). I'm still working on the stairs at home, maybe you have some ideas?

The screwdriver thing is not likely to happen and when it does touch both terminals it is done intentionally by someone. It normally has to be a BIG screwdriver.

I want y'all to know that I have already done everything I suggested here and still have all three fingers left <wicked evil grin>.

The only thing I've not done is to worry about all the "what ifs" (that aren't even likely to happen btw) that y'all keep bringing up.

That's me - Livin' on the EDGE.

[CapnLoki]

The problem in the original post was when Sleep_quest started talking about using a second battery with battery clips or using the jumper cables to connect to the Duracell. This completely defeats the safety aspects of the Duracell.

The cables are designed to be connected this way and to deliver much more current than will be handled when re-charging this way or powering the equipment (5-8 amps DC). The cables will handle starting current in the neighborhood of 300 Amps DC. Quite the margin of safety there.

I'm not talking about the ability of the wires to handle the current!

A box is a good idea and can be added at a later point when the poster is comfortable with the setup. They are not likely to find a box for $5 tho.

So you agree with me? I have nothing against testing this out with jumper cables; I've certainly used my share of bubble gum and bailing wire in a pinch. But we're talking about have a setup sitting in the bedroom, ready to be used in the middle of the night. For that I would require proper connections.

OK, perhaps the $5 box is a bit dated. But Walmart has several around $8. While there, check out the "MinnKota Trolling Motor Power Center" which includes cables, socket, breakers, etc. Add a battery and a "Battery Tender" and you're all set. With very little work you can have a high quality, 80 AH AGM backup, good for several weeks of service for about $300 total. Not too bad since the OP was talking about Lithium that would be $300 for 20 AH.

... The screwdriver thing is not likely to happen and when it does touch both terminals it is done intentionally by someone. It normally has to be a BIG screwdriver.

You're "you can get killed walking down the street" attitude is pretty lame. How about when your grandkid decides to serve breakfast in bed and puts the tray down on the battery next to the bed? It doesn't take a screwdriver; a curtain rod or lunch pail or coat hanger can short out a battery. And again, we're talking about leaving it in the bedroom indefinitely, not just pulled out to jumpstart a car.

I want y'all to know that I have already done everything I suggested here and still have all three fingers left <wicked evil grin>.

I have no problem with you doing stupid things. Go for it.

[Guest]

You're "you can get killed walking down the street" attitude is pretty lame.

You wanna see something lame? Read this....

Its obvious you've never seen this happen - it makes a big impression when a screwdriver turns red hot in a few seconds!

LOL maybe you need to poll people to find out who has this extremely long screwdriver "IN their bedroom" and talk to them.

if a cat knocked over a metal object in the middle of the night.

Do you know IF this poster even has a cat?

I don't know why I bother, it is clear you don't have an understanding of what this poster is trying to do but you "feel like" they need to do what YOU want them to do.

You and the other alarmists here need to "try" to tell people what they are asking about "before" y'all go off on your tangents warning what not to do and the world will end if they don't do things your way.

IOW - answer the question First.

[archangle]

Charging circuits are usually designed to limit charging current. You don't have this limit with a direct battery to battery connection.

You do in fact have the charging circuit of the car you are connected to.

The charging circuit of the car does nothing to limit the current from the car battery to the jumper battery. The battery can provide hundreds of amps even with the car engine not running.

[Guest]

Charging circuits are usually designed to limit charging current. You don't have this limit with a direct battery to battery connection.

You do in fact have the charging circuit of the car you are connected to.

The charging circuit of the car does nothing to limit the current from the car battery to the jumper battery. The battery can provide hundreds of amps even with the car engine not running.

I thought Loki explained that to you already...

All your points are correct to a degree, but the real problem is that you can't charge a 12V from another 12V. There will be a small current flow as the batteries adjust their charge, but nothing is really gained. As you point out there is the risk that a dead cell in one battery will kill the other, though this is not common with AGMs.

to a degree.

[archangle]

All your points are correct to a degree, but the real problem is that you can't charge a 12V from another 12V. There will be a small current flow as the batteries adjust their charge, but nothing is really gained. As you point out there is the risk that a dead cell in one battery will kill the other, though this is not common with AGMs. In general, batteries should only be "banked" together if they are the same type, and ideally the same size and age.

That will still work, although the charge rate gets slow as the battery voltages get close to the same. If you have a good connection, thick, short cables, and a fully charged source battery, you'll quickly get the jumper battery to a partial charge. You get quite a few amps with a small voltage drop with a car battery. You do need a proper charger to do the job fast and completely.

[archangle]

Charging circuits are usually designed to limit charging current. You don't have this limit with a direct battery to battery connection.

You do in fact have the charging circuit of the car you are connected to.

The charging circuit of the car does nothing to limit the current from the car battery to the jumper battery. The battery can provide hundreds of amps even with the car engine not running.

I thought Loki explained that to you already...

All your points are correct to a degree, but the real problem is that you can't charge a 12V from another 12V. There will be a small current flow as the batteries adjust their charge, but nothing is really gained. As you point out there is the risk that a dead cell in one battery will kill the other, though this is not common with AGMs.

to a degree.

Repeating your incorrect info doesn't make it more correct.

If the jumper battery is deeply discharged, its voltage may be low, and it will pull a lot of amps when you connect it to the car battery. For instance, if the jumper battery was run all the way down to 0 volts, it's basically acting like a short.

[Guest]

Repeating your incorrect info doesn't make it more correct.

I repeat hoping you will finally get it.

If the jumper battery is deeply discharged, its voltage may be low, and it will pull a lot of amps when you connect it to the car battery. For instance, if the jumper battery was run all the way down to 0 volts, it's basically acting like a short.

These things are designed to be connected when one battery is weaker than the other. Perhaps you need to discuss this with the manufacturer.

Have a Great Day

[archangle]

These things are designed to be connected when one battery is weaker than the other. Perhaps you need to discuss this with the manufacturer.

The jumper battery is designed to be connected to a discharged battery. Current will be limited by the current generating capacity of the jumper battery itself. When a fully charged car battery is powering a dead jumper battery, the car battery can produce a lot more current for a longer time than the small battery in the jumper battery.

The effect of current flowing into the jumper battery is different from the effect of current flowing out of the battery. The chemical reaction in the lead plates is proceeding in the opposite direction, so the heat produced by the chemical reaction will be different as well. There's also the potential of electrolyzing the water and producing hydrogen and oxygen gas if you supply a larger current than the charging process in the battery can handle. Too high a charging current can also overheat heat the battery and boil the electrolyte from simple resistive heating.

[Guest]

These things are designed to be connected when one battery is weaker than the other. Perhaps you need to discuss this with the manufacturer.

The jumper battery is designed to be connected to a discharged battery. Current will be limited by the current generating capacity of the jumper battery itself. When a fully charged car battery is powering a dead jumper battery, the car battery can produce a lot more current for a longer time than the small battery in the jumper battery.

The effect of current flowing into the jumper battery is different from the effect of current flowing out of the battery. The chemical reaction in the lead plates is proceeding in the opposite direction, so the heat produced by the chemical reaction will be different as well. There's also the potential of electrolyzing the water and producing hydrogen and oxygen gas if you supply a larger current than the charging process in the battery can handle. Too high a charging current can also overheat heat the battery and boil the electrolyte from simple resistive heating.

You are probably not gonna believe this from one of our many self-appointed experts...

The people who exaggerate the dangers of insignificant or nonexistent risks get people killed because they draw attention away from the actual health risks.

[HoseCrusher]

Theory and speculation often provide very interesting topics for discussion. However actual use generally brings things into sharper focus and you can then focus on the things that matter the most while also keeping in mind the bigger picture involved with the theories.

The idea is that if you push high current back into the jumper battery you could encounter problems. In actual practice as the current goes into the battery the voltages rises. When the voltage rises the current tapers off. This means that it should not be a "real" issue even though it could be construed as a theoretical possibility.

Also, over many years of using jumper packs and jumper batteries and charging them from the vehicle charging system after it got started I have never had an issue with hydrogen gas formation or exploding batteries as a result.

Of course your mileage may differ. It is important to be aware of the theory that something could possibly happen but in actual practice it is very remote that it would happen.