Help me with safely wiring my batteries together in parallel

[maxwolfie]

Hi all

I have two Ego batteries - both are 2.5AH “56V” (52V nominal) batteries. I understand that individually they are capable of 20A but wired together in parallel they can output 40A.

I will only ever connect them together when they are both fully charged

My motor will be a Toseven DM02, which I understand should be limited via the software to 15A or 18A, but for the purposes of wiring assume that I will limit at 20A.

For the wiring I assume 20A wiring would be fine, and I assume a 20A inline fuse would be fine.

What I am unsure about, though, is when I connect the batteries together, if there is a slight imbalance in the packs, could I potentially fry the wiring or blow the fuse? As in, would a brief surge of over 20A to equalise charge between the batteries be likely? Or even possible?

Also, I am planning on using the “S” models of anti-spark XT60S or XT90S. Are these overkill?

 

[chuyskywalker]

What I am unsure about, though, is when I connect the batteries together, if there is a slight imbalance in the packs, could I potentially fry the wiring or blow the fuse? As in, would a brief surge of over 20A to equalise charge between the batteries be likely? Or even possible?

If you plan to pull 20A, upsize the fuse a bit.

As for very momentary bursts, it's not a problem. (Most) fuses don't insta-pop over their labeled rating -- they often have to be pushed over that for X amount of time before they fail. Better sold fuses will come with charts that show how long it takes for the fuse to fail at various continuous (and instant) current levels.

Also, I am planning on using the “S” models of anti-spark XT60S or XT90S. Are these overkill?

There are no XT60 anti-spark connectors on the market (that I know of, been a few months since I last checked) so the XT90s is the only option there. And, for your purposes, they should work great. They tend to fail at higher pack voltages (I've burned out the resistor in several 72v setups) because they're undersized for that application, but at 52v they work great. Using the anti-spark also will alleviate any battery-to-battery fast charge spike because they'll slow the current.

Generally the best advice for dualing up batteries is to...just leave them paired. Charge and discharge them as a single unit and then most of this is a moot point.

 

[E-HP]

Generally shoot for 0.1v or less between packs before paralleling them.

 

[harrisonpatm]

Generally shoot for 0.1v or less between packs before paralleling them.

The equalizing current will be relative to the volt difference. At nominal 52v, if the actual voltage is about 1v different, you can expect to see a surge of current around 10A from the higher-voltage pack to the lower voltage one. This 10a will quickly decrease and level off. However, as mentioned before, just leaving and charging them in parallel all the time will avoid that issue entirely.

 

[Papa]

I have half a dozen or more Ego batteries, three 10's a 7.5 and mixture of smaller. I generally leave the larger paralleled, but carefully monitor charging. The BMS, of course, is bypassed when you parallel charge, so I solo charge in the OEM charger periodically.

 

[Justtrying]

I have half a dozen or more Ego batteries, three 10's a 7.5 and mixture of smaller. I generally leave the larger paralleled, but carefully monitor charging. The BMS, of course, is bypassed when you parallel charge, so I solo charge in the OEM charger periodically.

I have few questions about the ego 10’s. If I have them parallel in a razor dirt bike, can I just use the charging port and the charger that’s original came with the razor? If not how can I charge them without having to remove them everytime?

 

[eMark]

Hi all

I have two Ego batteries - both are 2.5AH “56V” (52V nominal) batteries. I understand that individually they are capable of 20A but wired together in parallel they can output 40A.

My motor will be a Toseven DM02, which I understand should be limited via the software to 15A or 18A, but for the purposes of wiring assume that I will limit at 20A.

Paralleling for output of 40A is irrelevant being your Toseven DM02 motor is limited to 15A-18A. The only advantage of paralleling is for increase in capacity (increase to 5.0Ah in mileage range) not power or speed. Assume your Controller at most is rated at 20A.

So, what is the advantage of paralleling the two Ego btteries? When one of the Egos is near LVC change over to the other Ego. Are you in that big of a hurry that you don't have 1-2 minutes to stop and switch batteries?

 

[Chalo]

So, what is the advantage of paralleling the two Ego btteries?

Cutting the per-battery discharge rate in half should result in better balance and longevity of the packs, and slightly increased range versus fitting them sequentially. It will also reduce the incidence of running either pack all the way down (which is damaging).

 

[eMark]

Cutting the per-battery discharge rate in half should result in better balance and longevity of the packs, and slightly increased range versus fitting them sequentially. It will also reduce the incidence of running either pack all the way down (which is damaging).

Easier said than accomplished AOK... depending in part on the condition of the cells in each 2.5Ah battery ... and your own DIY skill

"Good Luck ... Try Not To Blow Anything Up"​

 

[maxwolfie]

Cutting the per-battery discharge rate in half should result in better balance and longevity of the packs, and slightly increased range versus fitting them sequentially. It will also reduce the incidence of running either pack all the way down (which is damaging).

Wouldn’t there be MORE chance of running one of the packs below minimum (i.e. about 42V) while in parallel?

 

[Chalo]

Wouldn’t there be MORE chance of running one of the packs below minimum (i.e. about 42V) while in parallel?

No, because they'll match each other's voltages. So to run one all the way down, you would have to run them both all the way down. If you use them one at a time, it's likely that you would empty one before installing the other, even if you barely touched the second battery's capacity.

 

[eMark]

it's likely that you would empty one before installing the other, even if you barely touched the second battery's capacity.

That is already a possibility depending on the cycle aging condition of his two Ego packs.

Depending on the age of these two packs it's possible that one (or both) have already suffered some abuse resulting in voltage cell variances of 0.100v or more between the 14 cells. It's possible that at least one or more weak cells need to be replaced (25r?) before paralleling his two Ego packs.

Paralleling two aged packs of unkown (questionable) quality may not be the best solution until one first determines if there are any weak/bad cells that need to be replaced.

 

[E-HP]

The equalizing current will be relative to the volt difference. At nominal 52v, if the actual voltage is about 1v different, you can expect to see a surge of current around 10A from the higher-voltage pack to the lower voltage one. This 10a will quickly decrease and level off. However, as mentioned before, just leaving and charging them in parallel all the time will avoid that issue entirely.

Ya I messed up. I meant cells not packs. For my 14s, I shoot for 1 - 1.5v delta or less before connecting.

 

[eMark]

Ya I messed up. I meant cells not packs. For my 14s, I shoot for 1 - 1.5v delta or less before connecting.

Having a voltage variance no greater than 1.500v between the two Ego packs before paralleling is ok with packs having cells in good condition. Yes the two Ego packs will equalize while charging and hopefully during discharge, but is no indication of a weak cell that should be replaced.

It's still a good idea (when possible) to charge each pack (if questionable quality) within 0.100v of each other before paralleling. Even so it's still possible that one of both packs could have at least one or more weak cells.

Of course what's questionable pack quality to one person (pack voltage variance no greater than 1.5v) IS ok IF the quality of each cell is A-OK...