Dual parallel voltage difference, normal?

conanthewarrior

Gold Contributor
Member For 4 Years
Hi everyone.

I have been using my mechs a lot more lately, and enjoying them thoroughly.

However, my Abaddon and Diablo seem to be discharging the batteries unevenly, when I pull one is usually at 3.6-7V, the other up to 4V! The one with the lowest voltage is always the same side as the Atty.

I am much more used to regulated mods, amassing a lot of knowledge of them over the time of using them, but with mechs, I understand staying safe by building within my batteries CDR (usually well under), and they are a circuit, and general maintenance,but am not sure if this is normal. .

I rotate my cells left to right on each cycle, but this has happened a few times now.

It does seem that there is a bigger difference with a set of older cells, so I am wondering if it could be that.

I understand when stacking batteries, something like this would be dangerous, I just want to clear up if this is normal or not before I continue to use dual parallel boxes.
 

robot zombie

Silver Contributor
Member For 4 Years
The simple answer, is yes, it does happen. It's something that you should try to avoid, but nothing too significant.

Running a battery well past its CDR is much, much more dangerous than having your batteries drain unevenly in a parallel mod. I'm not entirely convinced that the latter is even dangerous at all under normal conditions. It's more of a performance issue. One battery will be more likely to go critical than the other, as it's giving more current and discharging lower. Just don't push them up to the CDR, use them for an unreasonably long time, or discharge to the point where the weaker one is hitting the bottom of its capacity and you will be just fine.

It's a natural occurrence, ime. It is my understanding that voltage differences aren't really as big a deal in parallel as they are in series (and even then, it's not as big a deal as once assumed.) You'll lose some headroom and overall push with the weaker cell, but it's not gonna blow on you. It just won't perform as well.

As cells age, you're going to see a greater voltage gap. No two cells are the same and no two cells wear down the same. A battery's wear is most evident in its capacity. The difference may be minimal to unmeasurable at first, but it will show as they wear down - one will usually lose capacity faster. If this is the case, then the solution is shorter discharge cycles. There should be a cutoff where their voltages will remain the same. Past that point, the gap will grow more and more. As you get closer to the bottom of either cell's capacity, the voltage will take a steeper dive. One will just hit that point sooner and thus get a head start on the other. With a little trial and error, you can figure out the point where they go out of sync.

That being said, all of my older pairs consistently have a greater gap. It's not unusual to see a .4-.5 difference when I take them down to 3.4-3.6v. Doesn't always happen, but it does happen. When I take them down to 3.8v, it's far less common and less severe... ...normally .2-.3 at worst. This usually starts setting in after around 2 months.

It could just be the mod itself... ...ideally, both paths should allow the same current, but if the difference in connection/conductivity is great enough, then one terminal might wear the battery out faster. I'd have to think you'd notice this pretty quickly. It would be evident after a single discharge cycle. No unregulated device is going to drain two batteries perfectly evenly. Rotating helps, but since no two batteries drain quite the same, the gap is inevitable. Sounds like this might be the case for you. Might try using those same batteries in another box.


Somewhat unrelated, I've had it happen sporadically with relatively new batteries... ...more often in series mods than parallel. Sometimes batteries that normally have tight voltages will suddenly show a .4-.6 gap. I'll usually just charge them at .5A and see how they do the second time around. Nice, slow charge. They consistently stay within .2v and usually .1v apart after that. I think it might just be a contact issue. It's like there's a bias between either the two negatives or the two positives... ...as in, one contact point from either end has better current flow than the other. I can tell you that when there's juice in the button on my noisy cricket, it can sometimes arc very mildly and intermittently. That might be enough to throw it out of balance with the other interfaces.

I dunno. That's just a thought. It's not based on facts or observations. I think I'm going to start noting the position of the battery with the lower voltage when this happens. Maybe mark which battery is which too, so I can see if it's limited to one battery in one orientation or if it's only one slot in the mod that actually dips either the battery faster.
 

conanthewarrior

Gold Contributor
Member For 4 Years
The simple answer, is yes, it does happen. It's something that you should try to avoid, but nothing too significant.

Running a battery well past its CDR is much, much more dangerous than having your batteries drain unevenly in a parallel mod. I'm not entirely convinced that the latter is even dangerous at all under normal conditions. It's more of a performance issue. One battery will be more likely to go critical than the other, as it's giving more current and discharging lower. Just don't push them up to the CDR, use them for an unreasonably long time, or discharge to the point where the weaker one is hitting the bottom of its capacity and you will be just fine.

It's a natural occurrence, ime. It is my understanding that voltage differences aren't really as big a deal in parallel as they are in series (and even then, it's not as big a deal as once assumed.) You'll lose some headroom and overall push with the weaker cell, but it's not gonna blow on you. It just won't perform as well.

As cells age, you're going to see a greater voltage gap. No two cells are the same and no two cells wear down the same. A battery's wear is most evident in its capacity. The difference may be minimal to unmeasurable at first, but it will show as they wear down - one will usually lose capacity faster. If this is the case, then the solution is shorter discharge cycles. There should be a cutoff where their voltages will remain the same. Past that point, the gap will grow more and more. As you get closer to the bottom of either cell's capacity, the voltage will take a steeper dive. One will just hit that point sooner and thus get a head start on the other. With a little trial and error, you can figure out the point where they go out of sync.

That being said, all of my older pairs consistently have a greater gap. It's not unusual to see a .4-.5 difference when I take them down to 3.4-3.6v. Doesn't always happen, but it does happen. When I take them down to 3.8v, it's far less common and less severe... ...normally .2-.3 at worst. This usually starts setting in after around 2 months.

It could just be the mod itself... ...ideally, both paths should allow the same current, but if the difference in connection/conductivity is great enough, then one terminal might wear the battery out faster. I'd have to think you'd notice this pretty quickly. It would be evident after a single discharge cycle. No unregulated device is going to drain two batteries perfectly evenly. Rotating helps, but since no two batteries drain quite the same, the gap is inevitable. Sounds like this might be the case for you. Might try using those same batteries in another box.


Somewhat unrelated, I've had it happen sporadically with relatively new batteries... ...more often in series mods than parallel. Sometimes batteries that normally have tight voltages will suddenly show a .4-.6 gap. I'll usually just charge them at .5A and see how they do the second time around. Nice, slow charge. They consistently stay within .2v and usually .1v apart after that. I think it might just be a contact issue. It's like there's a bias between either the two negatives or the two positives... ...as in, one contact point from either end has better current flow than the other. I can tell you that when there's juice in the button on my noisy cricket, it can sometimes arc very mildly and intermittently. That might be enough to throw it out of balance with the other interfaces.

I dunno. That's just a thought. It's not based on facts or observations. I think I'm going to start noting the position of the battery with the lower voltage when this happens. Maybe mark which battery is which too, so I can see if it's limited to one battery in one orientation or if it's only one slot in the mod that actually dips either the battery faster.
Hi there Robot Zombie, I always like your answers as they are in depth, good to see you on here.

I am glad it is nothing too significant, although I realise the biggest difference occurs on one of my oldest sets of 25R's. I think it may be time to recycle those and use some newer cells.

I never run past a batteries CDR, I feel that to be too unsafe, and I understood that with stacked cells, a voltage difference can be bad, but in this kind of set up, it is more an annoyance.
It is good to hear it will not blow on me, although I will be using a freshly married set of HE4's today and will see how big the difference is when I pull.

I gather it is like you say, and as the cells have aged, the capacity of one has dropped more than the other, I will try shorter cycles with the next set of cells to see if I can increase their life, and hopefully keep the voltage close together when I do pull them.

I would say it is definitely due to them being older then, as they are older than 2 months, so a new set seems to be the best option here.

I will try using the batteries in another box, but it does seem most likely to be the cells age as you have suggested resulting in the difference in voltage, I will ensure I rotate my cells like normal but as you say, no 2 batteries discharge the same.

That is quite odd that you have noticed it on series boxes, I am glad a slow charge at 0.5A seems to sort the issue though. The juice I gather could definitely be an issue there.

Ok, I will mark the battery that has the lower voltage, and see what happens, and if it is only on the side with the RDA or it occurs on both sides-this will allow me to know if it is the mod or the batteries.

Thank you for your help mate, and all the best, Conan.
 

zdawk

Member For 3 Years
Member For 2 Years
Member For 1 Year
I'm having the same issue with my Diablo right now. It was at the point where 1 battery was warm and the other was room temp. Has me a little concerned. I adjusted the screws on the positive side of the battery cavity speculating that it may have been an bad connection somewhere in there. Either way I'm on my first cycle after said adjustment so we'll see what impact it has.
 

conanthewarrior

Gold Contributor
Member For 4 Years
I would like to add I realise now the problem was worse in my Diablo VS the Abaddon, I got the two the wrong way round when I wrote this out.

The Diablo now is auto firing as soon as the battery cover is put on, so I think a little repair is in order. I just need to find a thin enough flathead to remove the top, and see what is going on.

The abaddon seems to be keeping batteries around the same voltage, so I think it was an issue with the device in question.
 

conanthewarrior

Gold Contributor
Member For 4 Years
I'm having the same issue with my Diablo right now. It was at the point where 1 battery was warm and the other was room temp. Has me a little concerned. I adjusted the screws on the positive side of the battery cavity speculating that it may have been an bad connection somewhere in there. Either way I'm on my first cycle after said adjustment so we'll see what impact it has.
I hope it helps, as it is a nice device and will be great to get working at its full potential for us both.

Let us know if you notice any improvement after the adjustments, I realise now my Abaddon is not doing the same, and seems to be discharging batteries at the same rate when I pull them for charging.
 

zdawk

Member For 3 Years
Member For 2 Years
Member For 1 Year
It does seem to have helped! I tightened them all the way down and put the batteries in (with a juiced up rda on it) and as soon as i put the battery cover on it started firing. So i pulled the batteries and rotated each screw a half to a quarter turn (the same to each screw) until I put the battery cover on and there was no rattle. I don't know if it was the systematic unscrewing or if by playing with the screws it fixed the connection, but there was only a .01 voltage difference when I put the batteries on the charger after about 18 hours of use. The issue of one battery heating up was resolved as well. Maybe give it a shot?
 

conanthewarrior

Gold Contributor
Member For 4 Years
It does seem to have helped! I tightened them all the way down and put the batteries in (with a juiced up rda on it) and as soon as i put the battery cover on it started firing. So i pulled the batteries and rotated each screw a half to a quarter turn (the same to each screw) until I put the battery cover on and there was no rattle. I don't know if it was the systematic unscrewing or if by playing with the screws it fixed the connection, but there was only a .01 voltage difference when I put the batteries on the charger after about 18 hours of use. The issue of one battery heating up was resolved as well. Maybe give it a shot?
Hang on-yours has started to autofire as well?

I am glad to hear that the tightening of the screws helped, however mine is having the issue that as soon as the battery cover is put on, it fires.
I was thinking this was likely the switch, but I am going to have a look at the contact screws to see if it is not the fire button, it may well be what happened with your device with the screws fully tightened.

A .01 voltage difference sounds fantastic, I hope I can get my Diablo within this level, as the Abaddon seems to be keeping batteries very close together when I pull them, so I am sure some tinkering with the Diablo can get it to within a reasonable level battery voltage wise.

I will try this out now, as I want to get it working again, I have a flathead that will fit these screws easily, but I do not have a long, thin flathead to actually remove the top of the mod to get to the switch, so if I can fix it with these screws it will be great. :)
 

zdawk

Member For 3 Years
Member For 2 Years
Member For 1 Year
yeah, the auto firing is from the screw on the button side being to tight. It's not the button itself. So, like i said I backed each screw out equally, in small increments until the auto fire stopped. Again, I'm not sure if it was getting the screws to be equally backed out or if it was moving the screws around made a better connection but it's much more betters now!
Good luck!
 

kim leith

Member For 4 Years
Member For 3 Years
Member For 2 Years
Member For 1 Year
The simple answer, is yes, it does happen. It's something that you should try to avoid, but nothing too significant.

Running a battery well past its CDR is much, much more dangerous than having your batteries drain unevenly in a parallel mod. I'm not entirely convinced that the latter is even dangerous at all under normal conditions. It's more of a performance issue. One battery will be more likely to go critical than the other, as it's giving more current and discharging lower. Just don't push them up to the CDR, use them for an unreasonably long time, or discharge to the point where the weaker one is hitting the bottom of its capacity and you will be just fine.

It's a natural occurrence, ime. It is my understanding that voltage differences aren't really as big a deal in parallel as they are in series (and even then, it's not as big a deal as once assumed.) You'll lose some headroom and overall push with the weaker cell, but it's not gonna blow on you. It just won't perform as well.

As cells age, you're going to see a greater voltage gap. No two cells are the same and no two cells wear down the same. A battery's wear is most evident in its capacity. The difference may be minimal to unmeasurable at first, but it will show as they wear down - one will usually lose capacity faster. If this is the case, then the solution is shorter discharge cycles. There should be a cutoff where their voltages will remain the same. Past that point, the gap will grow more and more. As you get closer to the bottom of either cell's capacity, the voltage will take a steeper dive. One will just hit that point sooner and thus get a head start on the other. With a little trial and error, you can figure out the point where they go out of sync.

That being said, all of my older pairs consistently have a greater gap. It's not unusual to see a .4-.5 difference when I take them down to 3.4-3.6v. Doesn't always happen, but it does happen. When I take them down to 3.8v, it's far less common and less severe... ...normally .2-.3 at worst. This usually starts setting in after around 2 months.

It could just be the mod itself... ...ideally, both paths should allow the same current, but if the difference in connection/conductivity is great enough, then one terminal might wear the battery out faster. I'd have to think you'd notice this pretty quickly. It would be evident after a single discharge cycle. No unregulated device is going to drain two batteries perfectly evenly. Rotating helps, but since no two batteries drain quite the same, the gap is inevitable. Sounds like this might be the case for you. Might try using those same batteries in another box.


Somewhat unrelated, I've had it happen sporadically with relatively new batteries... ...more often in series mods than parallel. Sometimes batteries that normally have tight voltages will suddenly show a .4-.6 gap. I'll usually just charge them at .5A and see how they do the second time around. Nice, slow charge. They consistently stay within .2v and usually .1v apart after that. I think it might just be a contact issue. It's like there's a bias between either the two negatives or the two positives... ...as in, one contact point from either end has better current flow than the other. I can tell you that when there's juice in the button on my noisy cricket, it can sometimes arc very mildly and intermittently. That might be enough to throw it out of balance with the other interfaces.

I dunno. That's just a thought. It's not based on facts or observations. I think I'm going to start noting the position of the battery with the lower voltage when this happens. Maybe mark which battery is which too, so I can see if it's limited to one battery in one orientation or if it's only one slot in the mod that actually dips either the battery faster.

Will using a potentiometer in a dual 18650 parallel set up cause any problems like this? Or will it help it?
 

robot zombie

Silver Contributor
Member For 4 Years
Will using a potentiometer in a dual 18650 parallel set up cause any problems like this? Or will it help it?
I don't think it would have any effect. All it does is throttle the power before it goes to the atty. Everything else still works the same on the battery end.
 

kim leith

Member For 4 Years
Member For 3 Years
Member For 2 Years
Member For 1 Year
Thanks. I read in a description on Ebay that a parallel set up with the potentiometer would push 6 volts when set at 100%, which is a nice voltage for me.
 

robot zombie

Silver Contributor
Member For 4 Years
Thanks. I read in a description on Ebay that a parallel set up with the potentiometer would push 6 volts when set at 100%, which is a nice voltage for me.
They must've mistyped. It would have to be series unless there's a boost circuit in there, too. Any pictures of it, namely the battery compartment?
 

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