BMS with Relay: Temperatures🔥 and power losses⚡ 

When I saw that resistor in the BMS my first thought was: built in pre-charge resistor ?! Niiice !! You know you can not simply connect battery to inverter. There would be a big inrush and spark that damages the capacitors in inverter and the battery too. Or if relay was off and switched on there would be a big spark/arc inside the relay. So if it is a precharge resistor that is a big plus for this BMS. That screws are totally OK. Also I think you would need at least a fan (or more) for the box. Cells hate heat. One of the main reason for cell degradation (see first Nissan Leaf problems/disaster there in Australia). BMS is now 30 Celsius, no airflow, plastic (so thermal isolating) case (you lock in all the heat) ... it will be HOT in there. And ... good job :)

yeah!!! "frog works" at the end 👍🐸 considering the losses and also as a safety measure (fire prevention) you should consider, in your design, a way to automatically shut down the inverter when you are away or even when the battery is low

Hallo, besten Dank für deine Videos! Ich bin durch Zufall darauf gestoßen und bin begeistert. Du hast eine tolle Art es zu erklären und deine experimentelle Vorgehensweise macht es echt sympathisch. Liebe Grüße aus Germany.

LOL. The end was hilarious.

It also could be the big resitor is there to charge the capacitors from an inverter before connecting. This to prevent high inrush currents.

Hi Andy. Love your show since years… I have installed a similar JBD BMS with relay and this is clicking all the time. Whether charging or discharging. Any idea what could be wrong ? PS. I asked our friends from “Ali-E” where I purchased it, but they do not reply accordingly. Thx for any insights. Keep up the good work ! Greetings from sunny south of France.

I think using a machine screw and nut as you have done is essential as it is SOOO easy to strip those threads.

The end was so funny, now pick those cells and put back where it came from. lol 😂👍

Andy you are a character. Lol. Hey, BTW, only 4 countries in the world use Fahrenheit so don't bother converting it only encourages them to not conform.

It seems that you are concerned about the relay causing heat, I personally wouldn't be, I would be looking at the 10W resistor but I don't think that you are going to see it heat up yet, if that BMS performs a top balance, then that means the best time to check for temperature is after the batteries have been discharged and have been charging and they are almost fully charged, check the voltages of the cells, you are looking for different charge states of the cells and at some point the BMS will start it's balance process in which it has to burn off some energy from the cells that are higher than the rest to keep everything on the level, if this BMS was an active balancer, it would be taking excess energy from the higher charged cells and moving it to the next cell which is a more efficient way of doing it but the one that you have is the older style and it wastes energy to achieve it's goal which is also when it should be producing heat! That's where you need to look, the relay isn't an issue... It might get warm but not 10W warm... I put an extra led which I just wired it to an existing led through a 470 ohm resistor in a headphone amplifier that I built, that extra led caused the quarter watt resistor to heat so much that the aluminium enclosure got really hot right above where the resistor was! It probably had about half a watt across it before it finally burnt out! I couldn't believe how much heat came out of that little thing! I have also used the 10W resistor in a high frequency crossover for a piezoelectric tweeter! While testing, it was on a piece of carpet, it burnt the carpet where it was sitting! So basically yeah! They can get very hot 🔥! It all depends on how unbalanced the cells are after being discharged, this will determine how hard that resistor has to work! So when you start using the battery, keep an eye on it for some time until you have some sort of understanding of what happens when it's actually working, if it's making to much heat! Grab yourself a temperature controlled fan controller circuit board from eBay, they are super cheap and some even have a variable speed output for the fan and will only use what it needs! A fan with a dust filter and another hole with filter for the exhaust, the temperature sensor on the BMS and the turn on and off temperature settings set... Done ✅👍 Some of those controller's can use the three and four wire computer fan's and control their speed while others simply have a mechanical relay for simple off and on operation, but mechanical relays won't last as long and there's only one speed! You can't tell just by the sound of the fan's if it's really hot 🔥 or it just warm... I hope that this helps 😊.

I agree that idle power is relatively low compared to other components' like inverter. The thing with the typical bms is the effective dc resistance. I am using Daly BMS and it has dc resistance of 20mOhms. At 100A, it would be 200Watts. My nominal battery voltage is 27V so it would be 2700 watts output with 200 watts loss. That's about 7.5% loss. So regardless of current, assuming all other parameters are constant, power loss would be 7.5%. I guess why there is a relay in addition/parallel with the mosfet. That's to minimize resistance at higher loads to minimize power loss. Note, there's more on the connections from connecting individual cells to the lugs etc. Crazy amount of power loss. 😂

If you look at the specsheet of that BYD relay (BYD EVR300CPES) then you can find out what the power consumption of that relay is as the reference. The relay contacts, the shunt, and the fuse will get hot too when you start pulling lots of loads.

i think that resister for inrush for inverter when you connect it as i seen a lot of people put a resister only when connecting the neg to the inverter to pre charge the caps .

Which BMS is this? It doesn't look like the JBD one I've got but you use the same app. Could be that the 24v is different than the 48v but figured I'd check since it would be nice if there was a relay on my bms that I didn't really know about

Have you connected cell 8 positive to cell 9 negative yet. Check the voltage of the battery at the main positive to the negative that goes to shunt.

Might be worth changing the battery in your Multimeter as it can screw with the reading when it's low. Also, the spec is probably pretty wide on cheap meters like that one.

Nice video, im waiting to see u finished instalación . 8:18 the resistor i think is for leth a litl amouth of current pass for charging the inveter capacitors (Big load like 900A in one sec normali triger the bms protección. I think dat resistor is for dat purpose for slow charge the capacitors of inverter and then switch on the relay. 11:31 i think u shold not disconect batery from bms with balance leads conected

Can you please find out the part number/the model of the relay/contactor? I want to check it out for my project. Thanks.

Excellent video! Thank you... Connecting solar charge controller and panels will negate any of those minimal losses. Without solar connected, I would shut it all down anyway. Question: How much solar do you need to fully charge that beautiful bank of batteries fully after a days use/drain? Have you tried draining the batteries all the way down and solar charging them yet? I look forward to the next step - the solar connection! LOL

If u split a hose u can cover busbars!

Love the Frog!!!

Great project! Do u thnik about a air circulation in the box? U can cut 2 holes one air in, the other air out, with 2 small fans...maybe depending on box temparaure, greetings from austria...not australia.. :-)

08:16 ten watt resistor?

Parasitic or phantom loads are a problem long term. You dont need that BMS. The low battery voltage cutout is adequately taken care of by the inverter/s. The high voltage charge cutoff is handled by the charge controller, your BMS is duplicating these functions at the expense of unwanted loading and complexity. DO install a balancer for piece of mind. My 12kw lifepo bank is within 30mv after 3 years of use with no activity from the balancer that I have seen.. Cheap square wave inverters are far more efficient with lower standby current and will perform well with lighting and resistive loads, toasters etc. A smallish low frequency sine inverter will handle electronic and inductive loads, these can be simply modified to give a higher surge rating to allow a lower current inverter to start the fridge or washing machine. , this two inverter approach also giving redundancy to increase reliability of the whole setup over time. Keeping it simple is the key in my experience. Interesting series though, good work and very enjoyable.

clever on the screw + nut for a stud!

Interesting relay in BMS. I have thought about something similar to use relays on solar charge input protects at 150v. Use a MOSFET in parallel to briefly handle load while switching the relay. No contact arching and low loss at high current.

The frog is the star!

If the bms can't dump the full charging current or back off the charger to a level it can 100% handle without disconnecting charger from battery bank it has no place in the design . You need a better BMS …. Or a diy sub controller . Polling the bms ( are you balancing any cells ? Yes/No ) . If yes lower the charge current & maybe a dump load . Note Reading the total bank voltage just isn't going to work !

Buy the studs!! Use the studs!!!

The 2000w Jackery and Bluetti were close to $2000.00 dollars few month ego. They call them solar generators. Now, the Frogy box provide 13kw of energy. It would be interesting to see how much each part cost and the total for the diy Frogy box in comparison with the factory made.

If the relay is out and you want to charge a flat battery, I imagine that resistor will allow a small charge until the battery voltage come up at which point the relay will be engaged.

Is it the coil voltage heating the bms? Could you put a resistor, or 12v bulb in series to lower the current/ voltage? As long as it's still functional! I was looking into latching contactors, it would require a reversable current to open or close the circuit, not simple to use with bms, I guess it could be used similar to a breaker, only it would be reset with voltage! Maybe a pushbutton reset? I may look into it again!!

I would assume that the BMS will heat up quite a bit more under constant medium to heavy load.

Maybe Kermit has some batteries! I'm sure he lives off grid!! I have a 🐢 turtle. Sheldon, he lives off grid, but so do I !!.. I guess he is a he , maybe he is a Shelly??

Whaaaaat? It's coming from South Dandenong? WTF, why? I would have thought that Brisbane would be a bit closer? I'm sure that they would have a mail distribution center there LoL...

I think that the 10W resistor is for discharging! It's rated for 10 ohms, a current shunt should be less than 1 ohm! Besides, the negative already has a shunt on it...

Actually, that external shunt.... You could literally take it apart and connect it's electronics to the shunt inside the BMS! That way you get rid some resistance as small as it is! It just takes out one more thing that has some resistance in the path because resistance = heat and heat is simply the evaporation of electricity! Which makes efficiency go down! But that's just me being an efficient thinking German LoL... It's probably why I drive a BMW... More efficiency = better performance and more mileage...

Great video yet again . Any chance of a update on your frogs. Did the one in the barbecue find a new home ? Lol

LOL... I'll be checking for the low battery sign next video ;)

Yeah i feel ya on the shipping part. Goes faster shipping from Germany to Sweden then from Sweden internally.

Your AA battery inventory looks exactly like mine.

You might as well use 50v for battery voltage - easier math. :)

From the cells in the last szene you can create another battery ... lol

Remember... Your BMS should always, always be doing it’s job when hooked up.. You unbalanced the batteries by pulling load from only 4 cells. I would think that the BMS would go into overdrive not knowing what was happening... just doing it’s job.

so many batteries

I think ur deliberately making all ur vids so complex to discourage the new guys from learning, very disappointed in u

My guess is that resister is for burning off the balance, Stand by current is just the cost of producing your own power, my inverter never shuts off so standby is just part of the load.