My 12v 280ah build thread

[HRTKD]

My cells are inside the RV. I added insulation to the larger solar/battery compartment and then insulated around the batteries too. The RV is at the storage lot, so it's going to get cold in the winter.

The smoker controller runs on AC, but it is an aftermarket system with multiple temperature probes. It's designed to activate a fan to push air into the smoker to adjust the temperature. I don't know that it could power the warming pads (too many amps probably), but a relay would solve that problem. It's from BBQ Guru. Mine is pretty old, no longer sold.

 

[HRTKD]

Updated my thread with the successful test I did today. Very pleased with the results. They're pretty close to yours.

 

[GSXR1000]

Here is mine before tidy it up. In a group 31 plastic box, which is now mounted to a camper. Plywood on bottom. Cells wrapped tightly with filament tape. I worry a bit about the buss bars, and not compressing the cells, but works for now. Ignore the lipo reading on display, it is only used temporarily to eyeball the cells. I also doubled up the buss bars since this picture. 250 amp switch breaker is mounted on outside of the box on the negative bms output.

do you have a link on the case you used?

 

[Electric Personality]

do you have a link on the case you used?

It was just a $9 group 31 case on Amazon.

 

[Sipma02]

Well, I may be wrong on some of my estimates. Turns out the lead acid battery i was using to temporarily power the heating pads was on its way out. It's been my test battery for many years now, and I think it finally bit the dust. I was noticing the heating pad was just not getting that hot—I was worried about my connections. I knew I would have a long draw of power, so I had the lead acid battery plugged into 120v power via a battery tender.
Before I pulled everything apart to check my heating pad, I remembered to check the easiest thing first—voltage. Turns out I was only getting around 8-11 volts into the heating pad. Even while the lead battery was plugged into the battery tender. So obviously that lead acid battery is bad. So I would imagine that with a proper ~13v into the heating pads, the temp will get a fair amount warmer.

To anyone following this thread, sorry for the uninformed data

 

[Sillyputty]

"sorry for the uninformed data"

Not uninformed, just data with less information. Now that you've followed up, we have more data. Thanks for sharing it.

 

[Sipma02]

So as I'm thinking about where to position my temp sensor for low temp disconnect on my BMS (Chargery BMS8T), I'm wondering if it would be smart to put 1 probe under the cells (right next to the heating plate) and one on top of the battery, with a goal of reading my battery temp more accurately.

The Chargery has 2 temp probes. I currently have them both on top, and generally don't see a variance of more than 0.5-1ºF between the two. I am thinking of moving one of the temp probes under the cells. The problem is that this would be in direct contact with the heating plate, giving a potentially skewed temp when the heating plate is on. Since I've never seen the temp of the heating plate get within a dangerously high range, I think it would work. Per my previous post (#36) I'm not expecting to see much more than a 20º-30º difference in temp between the top and bottom of my battery.

I think having one probe on top, and one on bottom would give a more accurate temp of the battery. Thoughts?

 

[HRTKD]

The second probe would be off by quite a bit while the heating plate is on, but it might be interesting to see what that temperature is. Hopefully it doesn't trip the high temperature disconnect.

 

[Luthj]

The probes should probably be placed mid-pack for one (on the side?), and then nearer to the top on the other side. That gets you a better picture. I wouldn't put them both on the same cell. I also suggest using a bit of silicone or other glue to adhere the probe to the case.

 

[Sipma02]

The second probe would be off by quite a bit while the heating plate is on, but it might be interesting to see what that temperature is. Hopefully it doesn't trip the high temperature disconnect.

Right, that is my main concern. Of course, the high temp disconnect is configurable, but I don't want to have to trick my BMS into working properly. I've never seen the heating plate go above 80º, which is well within safe limits.

The probes should probably be placed mid-pack for one (on the side?), and then nearer to the top on the other side. That gets you a better picture. I wouldn't put them both on the same cell. I also suggest using a bit of silicone or other glue to adhere the probe to the case.

The silicone or glue is a good idea. I'll do that. So you are suggesting one probe on the top left of the cell bank, and one on the bottom/middle right? So they are offset?

 

[HRTKD]

On my 4s battery, I put the temperature probes for the BMS and the thermostat in the (slight) groove between the two center cells. It's held down with tape. I then created a "cap" over the probes out of rigid foam insulation. I wanted the probes to get the battery temperature, not the ambient temperature.

 

[Bob B]

There is also a "difference of battery temperature" .... which can be adjusted also. I think the most it can be set at is 30 deg C. I'm not sure what that does other than trigger an alarm. The temperature alarms can also be turned off, but that wouldn't be desirable.

 

[Sipma02]

There is also a "difference of battery temperature" .... which can be adjusted also. I think the most it can be set at is 30 deg C. I'm not sure what that does other than trigger an alarm. The temperature alarms can also be turned off, but that wouldn't be desirable.

Yep, good call. I'd have to adjust that as well. I definitely don't want to turn off my temp alarms, but I think I feel comfortable adjusting the "difference of battery temp" to around 30ºF.

 

[Luthj]

The silicone or glue is a good idea. I'll do that. So you are suggesting one probe on the top left of the cell bank, and one on the bottom/middle right? So they are offset?

A good spot is right in the contact point between cells 1 and 2 (an inch or two from the bottom). Put the other on the opposite side, on cells 3&4, near the top. That should get you warning if one of the cells starts getting hot.

 

[Sipma02]

I haven't moved the temp probes yet (although I think I will), but I was pleasantly surprised this morning. Overnight temps were 1ºF, the coldest they've been all season. The cell temp (with both Chargery temp probes on top of the cells) were at 42.3ºF! Heating pads were fed 13.2v from my power supply. That's probably about the coldest ambient temps we'll see, and that will only happen in an emergency—our heater fails and van engine wont start. I would probably have more pressing concerns at that point.

I'm glad the heating pads + insulation was keeping the cells warm enough to be charged!

 

[charly]

what did you end up with regarding insulation?

 

[Sipma02]

I have 1/2 in XPS foam around 4 sides (3 vertical sides and the bottom). Unfortunately, the setup is surrounded by a metal casing that is attached to the vehicle body, which conducts significant heat away from the batteries.