Maximum Tesla S battery fluid pressure

[GyroGypsy]

My DIY RV system has used two Tesla S batteries for over two years with no issue. I am using a thermostat controlled aquarium fluid heater and DC pump to maintain at least 60 degrees F while using the internal battery thermistors for monitoring. This was initially tested to 10 degrees F here in Colorado. A simple pinwheel indicator monitors the flow of the RV antifreeze fluid used. Self priming Pump runs 24x7 and is submerged in the fluid reservoir. It is rated at 210 gph, but I am sure the battery flow restrictions limited this.

Over the last year, I noticed the pinwheel turning slower and slower. Last winter history showed more temperature variance than previous year. When I shut down and restarted the pump, the fluid would no longer flow through the batteries. A new pump makes no difference. I can blow 15 psi air through the system, and get old fluid blown out.

I am reluctant to try any higher air or fluid pressure until I can learn the battery internal pressure rating.

Does anyone have this value, or know a possible technical source?

Please don't reply with a lecture about system redesign using heating pads or different batteries.

System write up here if interested.

Tesla Coach Battery Installation - Why? How? - iRV2 Forums

I am asked numerous times about my system. I performed this upgrade in spring 2000. The COVID quarantine gave me plenty of free time, and it achieved my "5 C" goals of Capacity, Cubic Inches,

www.irv2.com

 

[noenegdod]

What are you using for coolant?

Sorry, I missed the RV antifreeze. That is apparently incompatible with the material in the cooling system. As for pressure, keep it as low as you can and start flowing something that will not corrode your system any further.

 

[noenegdod]

There is no way to give you a "safe" pressure at this point. Any pressure recommendation by anyone would be irresponsible. Once you have corrosion in the system the passage walls are not going to hold up to the same pressure clean uncorroded passages would.

 

[time2roll]

I would assume an automotive cooling system is designed for 15 to 18 psi at which point a release valve would open and spill coolant on the ground. I recommend reading up how to clean and flush the RV antifreeze and switch to ethylene glycol or even better the Tesla coolant. Verify pressure on a Tesla forum. I would assume there is a pressure cap similar to a common radiator system.

Is this an RV potable water pump? Could be 30 to 45+ psi.

 

[GyroGypsy]

There is no way to give you a "safe" pressure at this point. Any pressure recommendation by anyone would be irresponsible. Once you have corrosion in the system the passage walls are not going to hold up to the same pressure clean uncorroded passages would.

I just want to know the limit. What pressure I may actually use is my call, and my responsibility. No different than choosing my own value for a voltage setting when given the rated limit.

 

[GyroGypsy]

I would assume an automotive cooling system is designed for 15 to 18 psi at which point a release valve would open and spill coolant on the ground. I recommend reading up how to clean and flush the RV antifreeze and switch to ethylene glycol or even better the Tesla coolant. Verify pressure on a Tesla forum. I would assume there is a pressure cap similar to a common radiator system.

Is this an RV potable water pump? Could be 30 to 45+ psi.

I don't know if the Tesla liquid system is pressurized, but using my familiarity with other systems is exactly how I came up with the 15 PSI air test value. I am using ethylene glycol. The Tesla antifreeze was too viscous when I tried it two years ago. I am using an aquarium pump, just as been done often by other DIY systems. I could quickly pressure test it tomorrow. I don't think corrosion is an issue because high temperatures are never seen in my application. Nor is there any debris or discoloration in my fluid. I found where Tesla was initially flushing the batteries on a periodic schedule, but that practice is no longer followed. The chemicals used were not found in my search.

 

[time2roll]

Have you determined why the flow rate has decreased? That would be my primary concern.

 

[noenegdod]

A simple pinwheel indicator monitors the flow of the RV antifreeze fluid used.

I am using ethylene glycol. The Tesla antifreeze was too viscous when I tried it two years ago.

"RV antifreez" is propylene glycol, not ethylene and is intended to go in plastic plumbing. Its sole purpose is to prevent freezing and has essentially zero corrosion inhibitors.

I don't think corrosion is an issue because high temperatures are never seen in my application. Nor is there any debris or discoloration in my fluid.

Corrosion does not require high temperature. The blockage is caused by something. Is the system an open system? Could something have gotten in the tank and been pumped into the system. If not it is almost certainly corrosion.

I just want to know the limit. What pressure I may actually use is my call, and my responsibility. No different than choosing my own value for a voltage setting when given the rated limit.

I dont know what the spec is on pressure. You have gotten away with 15 psi so far. You can double that effective pressure with no increase in risk by drawing a vacuum on the other side if you have a vacuum pump. If you dont have a vacuum pump you can get ~3-5psi pressure drop by having someone blow high velocity air across the end of the outlet tube at an angle. If you are really creative and handy you can make a venturi vacuum and easily get 5 to as much as a 10psi drop.

 

[GyroGypsy]

"RV antifreez" is propylene glycol, not ethylene and is intended to go in plastic plumbing. Its sole purpose is to prevent freezing and has essentially zero corrosion inhibitors.


Corrosion does not require high temperature. The blockage is caused by something. Is the system an open system? Could something have gotten in the tank and been pumped into the system. If not it is almost certainly corrosion.



I dont know what the spec is on pressure. You have gotten away with 15 psi so far. You can double that effective pressure with no increase in risk by drawing a vacuum on the other side if you have a vacuum pump. If you dont have a vacuum pump you can get ~3-5psi pressure drop by having someone blow high velocity air across the end of the outlet tube at an angle. If you are really creative and handy you can make a venturi vacuum and easily get 5 to as much as a 10psi drop.

The system is closed, no sign of fluid contamination, but not truly sealed against pressure. I don't know about a true vacuum pump, but my shop vac may suffice. I have an accurate vacuum meter too. However, doesn't your premise require that no blockage is occurring?

 

[noenegdod]

Shop vacs move a ton of air but dont create a huge pressure differential. It would be of some help though.

The assumption is that you have a blockage. You have gotten away with 15psi on one side of the blockage. There are two ways to increase the pressure acting on the blockage to either push it out or increase the velocity of the fluid going past/through the blockage in an attempt to "sweep" it out.

First way is to increase the pressure you are putting into the tube. The second is to decrease the pressure on the other side of the tube. If you could draw a perfect vacuum on the other side of the tube, you now have 15 psi on one side and -15psi on the other resulting in the same effect as having 30psi on the inlet side and atmospheric pressure on the outlet side.

Just a word of caution: I may have been a bit cavalier with the assumption that just because you got away with +15psi on one side you could get away with -15psi on the other. A beer can will tolerate 15psi but will collapse under a lot less than a perfect vacuum.

 

[GyroGypsy]

Using my shop vac is a great idea, except more fabrication would be needed to capture any debris for analysis. Still will need to control its vacuum level and will likely need to add a relief port to outside air. This will take some fixtures and fittings. Used to have a nice vacuum pump, but it wandered off.

I have found another experimenter who used 20 psi fluid for leak testing, but runs system at 15 psi. He uses the Tesla pump which is PWM controlled.

I also have not tried alternating the pressure source between inlets. May perform same function, but easier. Perhaps a hunk of Teflon tape or other ? debris comes loose and into my receiving bucket.

 

[time2roll]

I would back flush to see if something will come back out. More pressure may wedge something in harder.

 

[GyroGypsy]

Long story short - batteries are now on the workbench. One battery flows about 900 ml/minute in both directions at 1 bar. The other battery only flows well in one direction, dribbles in the other direction.

I think this dispels corrosion theory, which would affect both batteries equally, and this indicates some form of blockage. I am going to rig up a suction system and try it's removal with 1.5 bar in the direction that flows. It would be nice to filter that flow just to trap whatever debris gets loose for a final determination.

Meanwhile if anybody has a suggestion for a better pump, that would be appreciated.

I also found a nice digital flow meter on Amazon that is normally used for liquid cooling a PC. However I have been unable to locate power wiring information. It has a three pin connector.

 

[time2roll]

Can the cooling system be disassembled at all? Last I recall Tesla had a ribbon/tape to move coolant between the cells. Is that still the case? I am thinking the block would be in the common manifold. Any chance to post a picture from the bench?

 

[GyroGypsy]

All fusible link wires would need to be removed to remove the flow manifold, then re-spot welded when done. Too much effort.

Here is the bad battery, but showing some flow in one direction. The other direction just dribbles.

 

[time2roll]

No one-way valve someplace? Did it previously flow better in both directions?
Do they both flow at 900?

 

[GyroGypsy]

No valve in one battery, and not the other. I am flowing hot water through both now, with no vacuum.

 

[GyroGypsy]

Another Tesla experimenter says I should get 6 lpm!

 

[GyroGypsy]

Shop vacs move a ton of air but dont create a huge pressure differential. It would be of some help though.

The assumption is that you have a blockage. You have gotten away with 15psi on one side of the blockage. There are two ways to increase the pressure acting on the blockage to either push it out or increase the velocity of the fluid going past/through the blockage in an attempt to "sweep" it out.

First way is to increase the pressure you are putting into the tube. The second is to decrease the pressure on the other side of the tube. If you could draw a perfect vacuum on the other side of the tube, you now have 15 psi on one side and -15psi on the other resulting in the same effect as having 30psi on the inlet side and atmospheric pressure on the outlet side.

Just a word of caution: I may have been a bit cavalier with the assumption that just because you got away with +15psi on one side you could get away with -15psi on the other. A beer can will tolerate 15psi but will collapse under a lot less than a perfect vacuum.

Noenegdod,

I tried shop wet-dry vacuum, and now see your point. It can only draw a couple inches of vacuum. I don't think I have any blockage remaining, but would like to increase water flow for rinsing out system while not increasing internal system pressure. I don't mind spending a bit for a regular pump like is used to recharge a/c systems, but suspect the return water will damage the pump. Ideas?

Any idea of normal Tesla battery system fluid pressure and flow rate?

 

[noenegdod]

Noenegdod,

I tried shop wet-dry vacuum, and now see your point. It can only draw a couple inches of vacuum. I don't think I have any blockage remaining, but would like to increase water flow for rinsing out system while not increasing internal system pressure. I don't mind spending a bit for a regular pump like is used to recharge a/c systems, but suspect the return water will damage the pump. Ideas?

Any idea of normal Tesla battery system fluid pressure and flow rate?

I use a robinair 5cfm vacuum pump for vacuum mixing gypsum products. So that I dont have to deal with moisture in the pump I have a 100lbs propane tank I pull a vacuum in, isolate the pump, and then open the tank to the mixing vessel.

You could do something similar just have the vacuum pump connected to one port on a tank and the water entering through another so the vacuum pump does not see any liquid water.

I would stick a valve between the battery and the tank, close it and pull the vacuum, open the valve for the water and then the vacuum. Good luck! hope it actually does something. Its a lot of work and money for nothing if it doesnt. Shop around for the pump. I know I paid 1/3 for mine what some people were trying to get.