Hooking Rigid Batteries in a series keeps blowing fuse when 2nd battery hooked up?

[unclejemima]

So i'm not sure what I'm doing wrong...I've done this before without issue in the past.

I've got 2x 18v rigid battery docks from amazon with pigtails that I've hooked up in a series. Whenever I hook up battery #2, it blows the fuse. I have 2 fuses (indicated by the circles in the diagram), and it always blows the same fuse when hooking up the 2nd battery, no matter the order of hooking them up.

So I'm no expert, but this should be pretty straight forward. I must be doing something wrong... Any advice?

If I hook up my meter to leads to "A" and "B" while hooking up only a single battery, I'm getting voltage...how is that possible? Technically shouldn't I get zero voltage at leads "A" and "B" until the 2nd battery is hooked up?

Any advice would be appreciated!

 

[lnanek]

Well this diagram is a ring from - to +, so if there was no fuse the combined battery pack would just short out all of its potential energy into heat until it reads zero volts. So not surprising it's blowing. You would need some sort of load like an ebike controller, heater, or a huge resistor to prevent that.

Re volt meters, they complete a circuit using a resistor to perform their measurements, something called a shunt. They don't measure the amount of current or voltage flowing through a circuit for you. Putting the leads at A and B is exactly the same as putting them on the right pack's terminals directly with nothing else hooked up. Before adding volt meter to a bare pack, nothing is flowing. After adding volt meter to a bare pack, some tiny amount of power is flowing into the volt meter so it can perform measurements.

Adding a volt meter to a running circuit just adds a parallel load into the volt meter's shunt. Doesn't do anything to the existing circuit.

 

[gromike]

Assuming points A & B are connected, you wired a dead short. Open point A and you should read the batteries in series voltage.
You need some resistance between the A or B connection.

 

[unclejemima]

Well this diagram is a ring from - to +, so if there was no fuse the combined battery pack would just short out all of its potential energy into heat until it reads zero volts. So not surprising it's blowing.

So it IS technically hooked up correctly. That kinda sucks...means this probably won't work and I should give up. I was hoping there was a problem with my wiring that I could correct.

I don't get how I can safely hook up 2x lead acid batteries without this issue, or is there always this short of potential energy when making the final hookup in the series?

I think I already fried one of the batteries so I may give up and just get a proper 36v battery. Sucks as I have done something similar in the past with no issue, not sure what's changing now.

 

[E-HP]

So i'm not sure what I'm doing wrong...I've done this before without issue in the past.

I've got 2x 18v rigid battery docks from amazon with pigtails that I've hooked up in a series. Whenever I hook up battery #2, it blows the fuse. I have 2 fuses (indicated by the circles in the diagram), and it always blows the same fuse when hooking up the 2nd battery, no matter the order of hooking them up.

So I'm no expert, but this should be pretty straight forward. I must be doing something wrong... Any advice?

If I hook up my meter to leads to "A" and "B" while hooking up only a single battery, I'm getting voltage...how is that possible? Technically shouldn't I get zero voltage at leads "A" and "B" until the 2nd battery is hooked up?

Any advice would be appreciated!

View attachment 380632

So your experiment to test which of the two fuses blow when intentionally short circuiting the batteries? I would move the fuse that isn’t blowing to the other location, and put the new one in its place, to see which blows then. Could be the one that’s not blowing is on the higher end of the tolerance range.

 

[unclejemima]

Well I give up.

So your experiment to test which of the two fuses blow when intentionally short circuiting the batteries?

Short circuit makes it sound like I have something hooked up wrong causing the short circuit.
My understanding is that the final hookup of any battery in a series causes a momentary short circuit???

Either way, I hooked up my ebike controller and tried again, hoping it that it would allow solve my issue by allowing the power somewhere to flow…but no go. I blew the same fuse, and toasted another battery! Oddly it’s the battery on the fuse circuit that does not blow that gets wrecked.

To bad. I thought hooking a battery in a series was straightforward…but now I’m down 2 batteries.

 

[A-DamW]

Any advice would be appreciated!

View attachment 380632

You are literally dead shorting the batts to each other.

Do what gromike said, disconnect point A, measure the series voltage between the wire.

 

[E-HP]

Well I give up.


Short circuit makes it sound like I have something hooked up wrong causing the short circuit.
My understanding is that the final hookup of any battery in a series causes a momentary short circuit???

Either way, I hooked up my ebike controller and tried again, hoping it that it would allow solve my issue by allowing the power somewhere to flow…but no go. I blew the same fuse, and toasted another battery! Oddly it’s the battery on the fuse circuit that does not blow that gets wrecked.

To bad. I thought hooking a battery in a series was straightforward…but now I’m down 2 batteries.

This is what a series connection looks like and where 36V can be measured.


Looks like the BMS for those batteries cost about $12 on AliExpress, so you could fix the batteries you killed.

 

[Hummina Shadeeba]

I hook up my meter to leads to "A" and "B" while hooking up only a single battery, I'm getting voltage...how is that possible?

ur measuring the voltage of one cell
If ur measuring between A and B.


But ur also shorting the red and black together at A.

 

[unclejemima]

Gentleman, I am a moron. I see that I WAS hooked up incorrectly. Sheesh. I have no clue what I was thinking!!
I’ve corrected my wiring and I believe the issue is solved.
Thanks guys.

 

[scianiac]

Are these batteries rated to be connected in series, some power tool packs are but some are not and one BMS shutting down can nuke the other's BMS with over voltage since you are applying twice the voltage it may have been designed for. Basically does Rigid sell tools that take two batteries and run at "40V" or something like that?