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overkill temperature sensors

John Frum

Tell me your problems
Joined
Nov 30, 2019
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When I set up my 24 volt battery with overkill bms I didn't put a lot of thought into the placement of the sensors.
Luckily I left them dangling off the bms for a few days and noticed that they indicated the same temperature.
That was a good baseline.
I decided to put one on a busbar and one on the side of a cell.

Upon reflection I think I will put one off the pack to measure the ambient temperature and leave the other on the cell so that I can see how much the cell temperature deviates from ambient.

Curious to hear other strategies.
 
On mine (they are still just hanging out there on top of the pack), but I was just going to leave them around that area, and tape them down, so maybe the tape acts like a barrier/insulator so the sensor more picking up from downward. Plus I figured if heat rises, then top of cell in middle of group should be an ok spot...

1623471055379.jpeg

I suppose it would be real easy to move it later if I thought it wasn't optimal...
 
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On mine (they are still just hanging out there on top of the pack), but I was just going to leave them around that area, and tape them down, so maybe the tape acts like a barrier/insulator so the sensor more picking up from downward. Plus I figured if heat rises, then top of cell in middle of group should be an ok spot...

View attachment 52514

I suppose it would be real easy to move it later if I thought it wasn't optimal...
Nice and neat build.
 
Nice and neat build.

Thanks.. I took a couple more pics tonight after I finished wiring in the breakers. I think for now I will leave those temp sensors right on top in the middle of the pack, and tape them down for now. When it is actually in service, I can use a IR temp gun and check around the pack to see how stable the temp is around various points like bottom-plate, sides, etc, to see how far off they drift from the location where the temp sensors are.

1623554938570.jpeg

1623554980855.jpeg

1623555146831.jpeg
 
When I set up my 24 volt battery with overkill bms I didn't put a lot of thought into the placement of the sensors.
Luckily I left them dangling off the bms for a few days and noticed that they indicated the same temperature.
That was a good baseline.
I decided to put one on a busbar and one on the side of a cell.

Upon reflection I think I will put one off the pack to measure the ambient temperature and leave the other on the cell so that I can see how much the cell temperature deviates from ambient.

Curious to hear other strategies.
Hey Joey , how are you ? On the previous JBD BMS that I reviewed there was only one NTC sensor on a fly lead and one embedded within the BMS. On the last batch that I received there are two sensors on fly leads for placement at one’s discretion. So I wonder if the internal one is still present - if not , maybe place one on the heatsink of the BMS and the other on a cell somewhere ? I also like your suggestion above for comparative purposes. Too many options but too few sensors ?.
 
Thanks.. I took a couple more pics tonight after I finished wiring in the breakers. I think for now I will leave those temp sensors right on top in the middle of the pack, and tape them down for now. When it is actually in service, I can use a IR temp gun and check around the pack to see how stable the temp is around various points like bottom-plate, sides, etc, to see how far off they drift from the location where the temp sensors are.

View attachment 52629

View attachment 52630

View attachment 52632
I like this build very much. So effectively you have 2 x 120A @ 12,8v . so I take it that each battery supplies its own load in isolation , as opposed to the two outputs being paralleled and running the risk of one BMS not being able to supply the load if the other fails ?
Also , where did you hide the BT module ? Cannot quite make out if it is behind the BMS ? Does the shielding effect and noise from the electronics not impact on the BT range ? Also noticed the additional serial port on the BMS so one can use both BT and RS485 at the same time. On the earlier models it was only one or the other - nice touch.
 
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Hey Joey , how are you ?
Fine thanks.
On the previous JBD BMS that I reviewed there was only one NTC sensor on a fly lead and one embedded within the BMS. On the last batch that I received there are two sensors on fly leads for placement at one’s discretion. So I wonder if the internal one is still present - if not , maybe place one on the heatsink of the BMS and the other on a cell somewhere ? I also like your suggestion above for comparative purposes. Too many options but too few sensors ?.
Just the two fly leads.
Makes sense to put one on the BMS heat sink.
 
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I like this build very much. So effectively you have 2 x 120A @ 12,8v . so I take it that each battery supplies its own load in isolation , as opposed to the two outputs being paralleled and running the risk of one BMS not being able to supply the load if the other fails ?
Also , where did you hide the BT module ? Cannot quite make out if it is behind the BMS ? Does the shielding effect and noise from the electronics not impact on the BT range ? Also noticed the additional serial port on the BMS so one can use both BT and RS485 at the same time. On the earlier models it was only one or the other - nice touch.

Thanks for the compliment, I just like things to look as neat as I can get them (for the time spent)...

Yeah, essentially it is just 2 independent batteries sharing one clamp. I will just parallel them and call it a 240a battery. I guess if half fails, my Magnum inverter would complain if I tried running a heavy load where I exceeded 120a and was pushing closer to its maximum of 250a input. Or I suppose if half failed, then Magnum will try to draw more than 120a and pop the 150a breaker on the other half (or the other BMS might shut off when it goes above 120a). I am not sure if these 120a Overkill BMSs can surge higher like say 150a for some brief time or if they just shutoff at 120a or whatever.

On the BT wire, if you look at the last pic, I have the wire twisted and just settles down in between the BMS mounting plate and the cells, it is just hanging there right now. I still need to try and connect the app to it and work on that part of it, so I haven't really determined if I would just leave it hanging there or mount it up higher in a way that it could broadcast farther distance...
 
Thanks for the compliment, I just like things to look as neat as I can get them (for the time spent)...

Yeah, essentially it is just 2 independent batteries sharing one clamp. I will just parallel them and call it a 240a battery. I guess if half fails, my Magnum inverter would complain if I tried running a heavy load where I exceeded 120a and was pushing closer to its maximum of 250a input. Or I suppose if half failed, then Magnum will try to draw more than 120a and pop the 150a breaker on the other half (or the other BMS might shut off when it goes above 120a). I am not sure if these 120a Overkill BMSs can surge higher like say 150a for some brief time or if they just shutoff at 120a or whatever.

On the BT wire, if you look at the last pic, I have the wire twisted and just settles down in between the BMS mounting plate and the cells, it is just hanging there right now. I still need to try and connect the app to it and work on that part of it, so I haven't really determined if I would just leave it hanging there or mount it up higher in a way that it could broadcast farther distance...
Great build and will follow your progress.
 
Looks like you choose to put a breaker on each battery. Is that instead of a breaker or fuse after they are joined in parallel, or in addition? And wouldn't the BMS provide the protection needed for each battery?
 
Looks like you choose to put a breaker on each battery. Is that instead of a breaker or fuse after they are joined in parallel, or in addition? And wouldn't the BMS provide the protection needed for each battery?

Yeah, I may also put on a breaker or fuse after they join (maybe it doesn't really need one though), I wanted each bank to have its own mechanical interrupter because I don't trust the BMSs per se, as their interruption is only transistor based, and if something failed where it couldn't close the gates, then the mechanical protection will override.

I wanted separate protection in case something shorts off one side it will just break it off the circuit, and the 2 packs won't be 'stuck to each other'...Supposedly these Overkill are 120a, so the breaker size I currently have in there is 150a, we'll see how that does I guess. I'm not an electrical engineer, just a tinkerer who has theories and tries things, to see if they stand the test of time hehe...

For my other 48v setup going into the house / shop, I have similar, with a Midnight Classic DC box (MNDC175-X2), each breaker going to a 16-cell battery bank... It also gives a way to break off a bank to do maintenance or something without killing power to LV6548 inverter pair, for more uptime.
 
Great build and will follow your progress.

I did try the BT module connection today, and I was sitting all the way out in the car outside the storage unit garage where the batteries are, and the phone app found the BMSs and was able to connect, so I don't even think it's a problem to have the BT modules stuffed down there behind the plates.
 
Nice build!

Did you check the breaker for working properly? I've seen lot of reviews complaining about the quality: even at 50% of its rated current it becomes very hot.

To be honest, I'd go for a regular fuse. Why would you need a resettable fuse? If it trips, something is seriously wrong. I would prefer fixing the cause than continuing to reset a breaker.
 
I don't live in any area where temperature sensing matters. If I did, one probe should be in the center of the pack (between cells) and another on the outside. As it cools to below freezing, the outside of the pack will reach 0 degrees before the center of the pack. But as it warms, the center may likely remain cold long after the external temp is above 0.
 
What is the floor of the pack made of ?

The floor plate is also aluminum, have two 2x4's underneath it to rest on. Not so much need for them on this 12v pack as it's short, but the 48v packs are 8 cells long, 2 wide, so resting on the 2x4's was to help ensure that I wouldn't get any abnormal bowing from the weight. I am going to stick the heat pads to the bottom center of those plates (those controllers have their own thermistors to place somewhere as well).
 
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Nice build!

Did you check the breaker for working properly? I've seen lot of reviews complaining about the quality: even at 50% of its rated current it becomes very hot.

To be honest, I'd go for a regular fuse. Why would you need a resettable fuse? If it trips, something is seriously wrong. I would prefer fixing the cause than continuing to reset a breaker.

I am planning to check out the breakers, supposedly these 'Stinger' breakers are supposed to be better quality, although not impressed so far. The conductors' contact point was slightly recessed below the boss, so when you set the terminal on it, it wouldn't quite touch (only on the nut side of it), so I had to install a copper washer under it to raise the surface up so the terminal makes good contact with it.

I'm gonna have to run some load through it and see if it stays cool, check voltage drop on it, etc... The main reason I like the idea of a breaker is for a switch, for easy on/off switch disconnection, but if I have any trouble with these, I may look into something else, possibly a fuse, since current flow without voltage drop is number one priority.
 
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I don't live in any area where temperature sensing matters. If I did, one probe should be in the center of the pack (between cells) and another on the outside. As it cools to below freezing, the outside of the pack will reach 0 degrees before the center of the pack. But as it warms, the center may likely remain cold long after the external temp is above 0.

I haven't had a chance to check out the detailed functionality of the app yet, but if Overkill gives the feature to adjust the charge cutoff temperature, then one could calibrate the cutoff temp to adjust for thermistor mounting location. Effectively, you could set it so that when the coldest point on the pack is at critical point (or a few degrees higher for safety), then if the point on the top of the pack where the thermistor is located may be say a couple degrees warmer, it would theoretically be calibrated where you wanted it to cutoff based on the difference between the actual thermistor location and the coldest point on the pack.

I am also going to have the heat pad on the bottom as well, so if they kick on, where I wanted them, then that is an extra blanket of safety. I may wrap an insulation around the whole pack in Wintertime, which may also help to keep the average pack temperature more balanced from center to edge? That's the idea anyways...
 
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