Batteries just arrived but have questions.

[MarkF]

Just received four 272 catl cells with 6m terminals and I’m top balancing them now. This forum has been a goldmine of information and huge help to me. This is my first battery build and have a few questions. The battery is going in my teardrop travel trailer.

1. I measured the depth of the cell terminals and they were drilled to 6.5 mm. All but one were threaded to 6mm which seams good but unfortunately one negative terminal is only threaded to 4.7mm. Should leave it alone or get a bottom tap and try to get another thread in the hole? Planning to use grub screws and loctite

2. I have an new overkill 4s BMS which has a discharge switch feature. Does this do exactly what it says or does it disconnect charging also? The reason I ask is I was planning to add a main battery disconnect but now wondering if this will take care of it.

3. I was originally planning to buy a victron smart shunt but it looks like this isn’t necessary with the information available on the overkill BMS Bluetooth app, right?

4. Is there a good calculator to determine what size lug you need if you want to crimp two 6awg marine wires together?

Thanks for any advice.

 

[Gazoo]

1. I measured the depth of the cell terminals and they were drilled to 6.5 mm. All but one were threaded to 6mm which seams good but unfortunately one negative terminal is only threaded to 4.7mm. Should leave it alone or get a bottom tap and try to get another thread in the hole? Planning to use grub screws and loctite

If you are confident you can tap without messing up the good threads then I would go for it. I used standard JB Weld to repair a stripped terminal with no threads and I was able to torque to 3nm. I had initially used loctite on that terminal. For me 3nm works but whatever you do limit the torque to around 4nm's. Some of the thread locker will ooze up for a short time after the grub screw is inserted. I wiped it off with a paper towel.

If I had to do it all over again I would use JB Weld. I know it's thicker than loctite but others have been able to screw the grub screw down all the way and then back off a quarter turn or so. If you don't tap the terminal then I would not back off at all. What happened in my case is the grub screw came up as I tightened the nut and I was using serrated flange nuts. Attached is a photo and you can see the loctite on the grub screw and the terminals threads next to it.

2. I have an new overkill 4s BMS which has a discharge switch feature. Does this do exactly what it says or does it disconnect charging also? The reason I ask is I was planning to add a main battery disconnect but now wondering if this will take care of it.

If you use the app from Overkills website then charging and discharging on/off can be controlled seperate from each other using the app. However if charging is shut off the FET's have to work harder with loads so if drawing high loads charging should be left on. I think if using the external switch both charging and dischage are cut off.

3. I was originally planning to buy a victron smart shunt but it looks like this isn’t necessary with the information available on the overkill BMS Bluetooth app, right?

I agree. The BMS is accurate enough but only after the cells are put through a full cycle. I recommend charging until the highest cell reaches 3.65 volts and discharging until the lowest cell reaches 2.5 volts. This will test the BMS to make sure the high voltage and low voltage disconnects are working. But note if you change any paramemter in the BMS the capacity will be thrown off and then you will need to run the battery through a full cycle to correct it.

All of the above is based on my own experience.

4. Is there a good calculator to determine what size lug you need if you want to crimp two 6awg marine wires together?

I can't help you with this one. I ordered my Overkill with the lugs crimped.

 

[OffGridInTheCity]

MarkF said:
4. Is there a good calculator to determine what size lug you need if you want to crimp two 6awg marine wires together?

Don't have a calculator but it so happens... that I put 2 x 6awg stranded copper wire into a single SelTerm 2awg lug - https://www.amazon.com/gp/product/B073CKHD9C/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
when I build my buss-bars for my battery packs and it fit's / crimps very nicely. So 2awg?

 

[MarkF]

Thanks for your replies and tips!

I bought a battery cutoff and will use it instead of the BMS shutoff. I already got a tube of 263 but will consider the jb weld.

Maybe I’ll pick up a bottom tap. I was just concerned about messing up the threads that were already there. It’s too bad they got 7 out of 8 perfect, perhaps I should consider myself lucky for 7 good ones!

My batteries didn’t come with m6 x 20 grub screws and will pick some up. I got a beam type inch pound torque wrench but chickened out at 2nm thinking it was tight enough for top balancing with the supplied brass bolts. I’ll do it right with serrated nuts and cemented grub screws.

BTW I got overkill to install 1/4” lugs on the BMS so the two 6wag wires in one lug is for the starter batter lead to a new Victron Orion smart 30 amp charger in the RV. I have one 100w solar suitcase but want some juice when traveling between campsites. I don’t have an inverter so most of our loads are small. We have a 12v fridge, fan and lights and want to camp off grid for 5 or so days…so I I’m hoping we’re covered.
I didn’t get a device to discharge/test the battery so outside of running things on the camper, I’ll not be able to place a meaningful load on the battery to cycle it.

Thanks again for the advice!

 

[Just John]

1. I measured the depth of the cell terminals and they were drilled to 6.5 mm. All but one were threaded to 6mm which seams good but unfortunately one negative terminal is only threaded to 4.7mm. Should leave it alone or get a bottom tap and try to get another thread in the hole? Planning to use grub screws and loctite

Depends on how confident you are about success, you could certainly use the extra thread depth.

2. I have an new overkill 4s BMS which has a discharge switch feature. Does this do exactly what it says or does it disconnect charging also? The reason I ask is I was planning to add a main battery disconnect but now wondering if this will take care of it.

Should be both, a charge and discharge switch. They will work independently, so it is what you want.

3. I was originally planning to buy a victron smart shunt but it looks like this isn’t necessary with the information available on the overkill BMS Bluetooth app, right?

I would check and see if it is accurate enough, but no sense in spending money you don't have to.

4. Is there a good calculator to determine what size lug you need if you want to crimp two 6awg marine wires together?

Depends on the brand of lug. I've used 4 gauge to crimp two 6 gauge with good success. If you find the chart/calculator, let me know.

 

[MarkF]

If you are confident you can tap without messing up the good threads then I would go for it. I used standard JB Weld to repair a stripped terminal with no threads and I was able to torque to 3nm. I had initially used loctite on that terminal. For me 3nm works but whatever you do limit the torque to around 4nm's. Some of the thread locker will ooze up for a short time after the grub screw is inserted. I wiped it off with a paper towel.

If I had to do it all over again I would use JB Weld. I know it's thicker than loctite but others have been able to screw the grub screw down all the way and then back off a quarter turn or so. If you don't tap the terminal then I would not back off at all. What happened in my case is the grub screw came up as I tightened the nut and I was using serrated flange nuts. Attached is a photo and you can see the loctite on the grub screw and the terminals threads next to it.


If you use the app from Overkills website then charging and discharging on/off can be controlled seperate from each other using the app. However if charging is shut off the FET's have to work harder with loads so if drawing high loads charging should be left on. I think if using the external switch both charging and dischage are cut off.


I agree. The BMS is accurate enough but only after the cells are put through a full cycle. I recommend charging until the highest cell reaches 3.65 volts and discharging until the lowest cell reaches 2.5 volts. This will test the BMS to make sure the high voltage and low voltage disconnects are working. But note if you change any paramemter in the BMS the capacity will be thrown off and then you will need to run the battery through a full cycle to correct it.

All of the above is based on my own experience.


I can't help you with this one. I ordered my Overkill with the lugs crimped.

Ouch, I saw this and read your earlier posts on this. That really stinks and hope I don’t have this happen to me.