Updated 24V System Diagram with Fortune cells, Temp control, Battery heater, etc

Starry-Nights

New Member
Joined
Nov 4, 2019
Messages
18
Had a couple of older threads on my layout including one that got Will to post a solution with a relay to get around problem of small BMS cables needing to handle large inverter draws. An update is needed; a lot has changed.

This is my 1st system, and owe a huge thanks to Will for the videos that kept me up many nights and helped me make choices. I bought many major components including the 8 Fortune cells, Daly BMS, inverter and Sterling B to B from Electric Car Parts Co. They have been great, offering excellent near instant knowledgeable support. The Fortune cells with the many bus bars made the battery super easy to build and it has performed flawlessly. The inverter is similar to the AMS ones, but ECPC gets them directly from the source company, Sigineer, with a better configuration and price. The owner actually visits China often to work with suppliers. You even stand a good chance of him answering a support or sales inquiry call!

BMS WITH RELAY CONTROL? First, I did install a 500amp relay per Will's diagram and recent video, but it (relay) failed instantly. Returned. When I mentioned concern about amp load through Daly BMS to Electric Car Parts, they said cables and insulation were really good and since short should be able to handle large load. OK, I tested, running both induction cooktop and heat gun at same time. Cables remained cool, but there was a problem - the 250 amp breaker to the inverter trips after about 2 minutes! I think this is a defective cheap breaker because the 3000W inverter display was showing it was at just 80% load. Since I rarely would ever be using over 2000 watts and disliked the complexity of the constantly-powered relay in the system, decided to not use a relay. I will keep an eye on temps and change if there is an issue. https://www.wirebarn.com/Wire-Calculator-_ep_41.html would seem to confirm the short BMS cable length is able to handle the load, even with a 1% drop.

LOW TEMP CONTROL: I live in NH and have been building a Sprinter van so I could spend winter months in Arizona, but unfortunately a surprise health issue will have me grounded until May, about the time it is wonderful here. So, Van is in driveway getting froze and snowed on. Since the Daly BMS has no low temp control, I added an inexpensive thermostat that cuts charging at 35 degrees and resumes at 37. Works flawlessly. To improve things, enclosed battery in foam insulation board and added a small 12 volt RV elbow pipe heater (https://www.amazon.com/gp/product/B01N6N721Y/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1) Have it under a 3/16" aluminum sheet that acts as heat spreader. The tiny heater cannot keep up with really low temps, but if you give it a head start and it gets up to say 40F, it will usually not fall to the cut-off temp unless it drops into single digits. The fact that it needs a head start makes it difficult to control thermostatically, but current draw is so low, I've just been leaving it on. Options would larger heater or add 2nd one. Of course, this would not be an issue if I was in Arizona now!

System seems to be working really well and love flexibility of charging options beyond solar, despite the fact these are hardly needed. Hope to see Will review the Sterling B to B unit sometime; there is certainly a huge difference in review scores on Amazon. At the time Renogy didn't offer a 12v to 24v B to B solution, and I don't think they have one now. Sterling is widely used in Marine which I am coming to realize is a much tougher environment!
 

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KG6S

ELI the ICE man
Joined
Dec 22, 2019
Messages
85
Location
Nevada's Gold Discovery Site
This is good news. I've been stewing on the issue of a relay versus none on the Daly 200A BMS. I'm going to bench test my setup without the relay. According to your link the 6 AWG is just barely adequate, but adequate. Thanks for the post.
 

Starry-Nights

New Member
Joined
Nov 4, 2019
Messages
18
Will be interested in your results! Broken wrist currently prevents me from replacing the faulty breaker and doing more tests myself. In prior tests drawing 1500 watts for 15 minutes everything remained cool. Remember, I have 24V system; a 12V one would need to handle 2X the Amps.
 

diyernh

Solar Enthusiast
Joined
Feb 5, 2021
Messages
111
Had a couple of older threads on my layout including one that got Will to post a solution with a relay to get around problem of small BMS cables needing to handle large inverter draws. An update is needed; a lot has changed.

This is my 1st system, and owe a huge thanks to Will for the videos that kept me up many nights and helped me make choices. I bought many major components including the 8 Fortune cells, Daly BMS, inverter and Sterling B to B from Electric Car Parts Co. They have been great, offering excellent near instant knowledgeable support. The Fortune cells with the many bus bars made the battery super easy to build and it has performed flawlessly. The inverter is similar to the AMS ones, but ECPC gets them directly from the source company, Sigineer, with a better configuration and price. The owner actually visits China often to work with suppliers. You even stand a good chance of him answering a support or sales inquiry call!

BMS WITH RELAY CONTROL? First, I did install a 500amp relay per Will's diagram and recent video, but it (relay) failed instantly. Returned. When I mentioned concern about amp load through Daly BMS to Electric Car Parts, they said cables and insulation were really good and since short should be able to handle large load. OK, I tested, running both induction cooktop and heat gun at same time. Cables remained cool, but there was a problem - the 250 amp breaker to the inverter trips after about 2 minutes! I think this is a defective cheap breaker because the 3000W inverter display was showing it was at just 80% load. Since I rarely would ever be using over 2000 watts and disliked the complexity of the constantly-powered relay in the system, decided to not use a relay. I will keep an eye on temps and change if there is an issue. https://www.wirebarn.com/Wire-Calculator-_ep_41.html would seem to confirm the short BMS cable length is able to handle the load, even with a 1% drop.

LOW TEMP CONTROL: I live in NH and have been building a Sprinter van so I could spend winter months in Arizona, but unfortunately a surprise health issue will have me grounded until May, about the time it is wonderful here. So, Van is in driveway getting froze and snowed on. Since the Daly BMS has no low temp control, I added an inexpensive thermostat that cuts charging at 35 degrees and resumes at 37. Works flawlessly. To improve things, enclosed battery in foam insulation board and added a small 12 volt RV elbow pipe heater (https://www.amazon.com/gp/product/B01N6N721Y/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1) Have it under a 3/16" aluminum sheet that acts as heat spreader. The tiny heater cannot keep up with really low temps, but if you give it a head start and it gets up to say 40F, it will usually not fall to the cut-off temp unless it drops into single digits. The fact that it needs a head start makes it difficult to control thermostatically, but current draw is so low, I've just been leaving it on. Options would larger heater or add 2nd one. Of course, this would not be an issue if I was in Arizona now!

System seems to be working really well and love flexibility of charging options beyond solar, despite the fact these are hardly needed. Hope to see Will review the Sterling B to B unit sometime; there is certainly a huge difference in review scores on Amazon. At the time Renogy didn't offer a 12v to 24v B to B solution, and I don't think they have one now. Sterling is widely used in Marine which I am coming to realize is a much tougher environment!
I'm trying to wrap my head around heating LiFePO batteries. My install(s) are similar, but using 24V solar to 12V, along with standard camper converter (12V from 120 plug in).

I have tried to solve the battery issue with my entire system design. I have the solar panels heating the battery, then after the battery is warm, charging the battery. But if someone comes into camp at night, cold, and plugs into 120VAC, the 60A charging circuit will try charging the battery, and there is no heat to the battery. Your vehicle battery to 24 battery seems to be the same issue. If you want to use the camper in the winter, no solar available, the vehicle would not charge the 24V battery until springtime. The battery will discharge, but never charge until solar heats it, or it gets warm. Worse yet, some of the complete batteries sold have BMS systems that either don't have good temperature sensors, or turn on charging too low, possibly killing the battery.

I believe this needs to be a canned module, that is installed for LiFEPO, but not needed for lead acid. This module would probably be a diode to let power out of the battery, but none in when cold. When it's cold, AND charging power is applied, the heaters turn on. When it's warm, the diode is bypassed, power in/out as needed. There is some logic in this that the heaters don't turn on except when cold AND charging power is available. Might was well add the logic of not charging the battery when it's cold (redundant to a good BMS/sensor). We wouldn't want the heaters on when in storage, running from battery power as it would kill the battery in short time. The heaters should only be powered from the charging source. This module should be "Idiot Proof" to allow anyone to not know it's there, Possibly it could add a warning light connection saying "Battery Cold, Charging system inhibited" to inform users that they may be short on battery power.

I've looked at Wills videos, and it doesn't appear to me that the BMS temperature sensors are reading the actual battery temps. SOK has the sensor on the metal case, not thermally conductive to the cells and insulated to the ambient air. Big Battery is similar, ambient sensor. You can easily heat the thin case, and ambient air, but the cells could still be really cold. In military Environmental Screening surveys, we put the thermocouple on the mass, insulating it from air with several layers of cloth tape. It takes quite a while to heat the solid mass, air is quick. I'm thinking most BMS temperature sensors are not reading correctly and will damage the cells when charging them cold.

So, in your case.... If you are out of commission, and you have someone move the Sprinter to plow the driveway. They turn on the heat and let it idle while plowing. The van heat would heat the air, which would pass by the battery case. This would heat up quickly, with the air near the BMS sensor. The BMS turns on charging at full amperage because the battery was low. Wouldn't this charge the cells when they are too cold, with a high amperage? I'm similar if someone runs the generator to warm the 5th wheel, heater, and big converter for battery charging.

I think this will need to be a module, directly inline with the LiFEPO battery. This will probably be a few hundred $ to get power diodes, etc enough to handle the output amps on the batteries. If I go back to AGM's, this would be removed.

I think this will need to moved to another thread if there is more interest in a LiFePO battery heating diagram/schematics/module/kit... It would be easier to find and some company could take our engineering and sell it.

I'm in NH, with an off grid camp north of Utica in the Adirondacks. Worst case temps are -36C. Sunlight is scarce with Solar panel angles at 23 degrees from vertical. I'm thinking it would be several sunny days with 600W panels to heat up a battery to 0C.
 

HRTKD

Boondocker
Joined
Apr 24, 2020
Messages
6,497
Location
Somewhere South of Denver
My Overkill Solar BMS has an external temperature sensor and reads the battery temperature directly.

UltraHeat, through their distributor Annod Industries, sells a kit for warming batteries. I implemented that kit. As I put it in use it evolved. It has been in place for a few months and is working well. My writeup can be found here:

 

Starry-Nights

New Member
Joined
Nov 4, 2019
Messages
18
Outside temps at my home in NH are a lot milder than the what you are experiencing! Also, I wasn't camping in my van during winter so battery draw was tiny and the little sun I got was enough to keep charged.

The Sterling B to B charger supplies 24V on a Lithium curve to the house battery. But, you are correct that if the battery temp falls below freezing, I could have a problem if I ran the engine since it is not thermostacally controlled.. I solve this by manually turning off the Sterling in the winter and do not plug the Inverter/Charger into shore power. The temp sensor for the thermostat controlling input from solar panels to battery is placed in between the Fortune cells (there are air gaps) plus, as a cross-check, I have a second sensor that leads to a wired indoor/outdoor thermometer; these are usually within 1 degree of each other.

As I stated before, I have the 7 watt heater under the battery in an insulated case. If I were in your situation, I might try a second heat strip or one that could be selectively switched on as needed. This setup heats battery much faster than waiting for an outside source to gradually get to the battery under the sofa bed. Remember, my heat strip is on continually and normally gets the battery well into 40's during daytime when it is warmer, and at night, it cools off slowly, but will fall below freezing when outside temps fall to single digits or below.

This winter I have a MUCH better solution - Drove the van from NH to the Arizona desert, arriving New Years day. I am in free BLM (Bureau of Land Management) camping areas and enjoying a great life! I'll come back in late March. Made a quick video:
 

diyernh

Solar Enthusiast
Joined
Feb 5, 2021
Messages
111
Outside temps at my home in NH are a lot milder than the what you are experiencing! Also, I wasn't camping in my van during winter so battery draw was tiny and the little sun I got was enough to keep charged.

The Sterling B to B charger supplies 24V on a Lithium curve to the house battery. But, you are correct that if the battery temp falls below freezing, I could have a problem if I ran the engine since it is not thermostacally controlled.. I solve this by manually turning off the Sterling in the winter and do not plug the Inverter/Charger into shore power. The temp sensor for the thermostat controlling input from solar panels to battery is placed in between the Fortune cells (there are air gaps) plus, as a cross-check, I have a second sensor that leads to a wired indoor/outdoor thermometer; these are usually within 1 degree of each other.

As I stated before, I have the 7 watt heater under the battery in an insulated case. If I were in your situation, I might try a second heat strip or one that could be selectively switched on as needed. This setup heats battery much faster than waiting for an outside source to gradually get to the battery under the sofa bed. Remember, my heat strip is on continually and normally gets the battery well into 40's during daytime when it is warmer, and at night, it cools off slowly, but will fall below freezing when outside temps fall to single digits or below.

This winter I have a MUCH better solution - Drove the van from NH to the Arizona desert, arriving New Years day. I am in free BLM (Bureau of Land Management) camping areas and enjoying a great life! I'll come back in late March. Made a quick video:
Thanks for the video. I hope to be out there when I retire. I'm investing now in some of the things for this, (Camper, Solar, etc). I do love the Adirondacks in the winter though. I was up there a couple of years ago. -15 to -25F. At night, everything twinkles with a headlamp light. The frost on the Christmas trees, stars out. The -36C is the Adirondacks, weather channel max low. I've never been there at that day/night. The battery and solar need to work unattended.

I've tried to have manual logic control on systems. It's failed. I have checklists to ensure that these manual actions happen, but I sometimes forget. Trying to give your wife, kids, friends a checklist is useless. Their eye's glaze over and it isn't done. I'd give it the first time my wife/kids started the truck, they wouldn't shut off the Sterling. If they shut if off, it wouldn't ever be turned on again. Too much to remember, too complex. Things get broken and I have to either replace things, or ban anyone from touching anything.

I'm okay with using the battery power to heat the battery to get the solar charge. This would need to be in expectation that I could heat the battery, then immediately charge it back up. That would be more complex than just using the external charging power to heat, then switching to charging the battery once it's warm.

This is an issue with all LiFePo batteries. The Battle Born heated batteries have a switch for someone to turn on the heaters. It would be difficult to have someone only turn the switch on several hours before starting the vehicle, or it gets sunny for solar. It would be more difficult to ensure it is turned off when you leave for a while.

Engineering a solution would eliminate the manual requirements. It does take some time to get it right. The best solution is that the user doesn't know what is being done and never knew they had a problem.

https://www.amazon.com/Engineer-Solving-Problems-Methods-Understand/dp/1731526717

:)

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HRTKD

Boondocker
Joined
Apr 24, 2020
Messages
6,497
Location
Somewhere South of Denver
I've tried to have manual logic control on systems. It's failed. I have checklists to ensure that these manual actions happen, but I sometimes forget. Trying to give your wife, kids, friends a checklist is useless. Their eye's glaze over and it isn't done. I'd give it the first time my wife/kids started the truck, they wouldn't shut off the Sterling. If they shut if off, it wouldn't ever be turned on again. Too much to remember, too complex. Things get broken and I have to either replace things, or ban anyone from touching anything.

My goal in my RV's system was that no instructions are necessary. So far, there's no intervention required, unless the (optional) portable solar panels are deployed. For that, a circuit breaker has to be flipped on, but I could just as easily leave that breaker flipped on all the time, eliminating that step.
 
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