Yet another inverter question

[woodlecj]

Just started dabbling in this for a Man-shed. I referenced some of the doc's that FilterGuy alluded to. If I'm using a 12V 100A Lifepo and I use the formula 2000W/.9/12 = 185A. The battery claims a 1C discharge rate of 100A. How do I protect the battery? Is a 1000W inverter a safer bet?

In my testing yesterday I totally forgot about discharge rate and ran the heat gun at full blast for about 10 min. Shunt meter showed 12.07V @128A! Inverter was happy, battery was happy. Battery BMS did not shut it down. I hope I didn't shorten the life of my new battery.

Thx,

 

[Ampster]

You are the only one that can protect the battery by the loads you use. I don't think a small discharge above 1C for a few minutes is going to shorten the life. A smaller inverter will not be worth the investment. More batteries would be a better investment because you would have more capacity.

 

[John Frum]

A 100 amp hour battery likely has a BMS that will be stressed to the max passing 100 amps.
Same BMS will probably trip on 30 seconds at 120 amps.
Unless you know your inverter has a programmable low voltage disconnect you should do the math like this.
1000 ac watts / .85 conversion factor / 10 volts low cutoff.

 

[Alice2021]

Usually,small inverter no load current is smaller than bigger inverter,for example,1000W pure sine wave inverter noload current is about 0.5A, but 2000W pure sine wave inverter no load current is about 1.5-2.5A.So if your appliance is small, you can change another 1000W pure sine wave inverter

 

[magicmike]

Just started dabbling in this for a Man-shed. I referenced some of the doc's that FilterGuy alluded to. If I'm using a 12V 100A Lifepo and I use the formula 2000W/.9/12 = 185A. The battery claims a 1C discharge rate of 100A. How do I protect the battery? Is a 1000W inverter a safer bet?

In my testing yesterday I totally forgot about discharge rate and ran the heat gun at full blast for about 10 min. Shunt meter showed 12.07V @128A! Inverter was happy, battery was happy. Battery BMS did not shut it down. I hope I didn't shorten the life of my new battery.

Thx,

Try a fuse between the battery and the inverter. As close to the battery as possible. Also check on the inverter if it has low cut off on it and that u active it the battery should have a low battery cut off on the bmi. Check that is turned on. Make sure the inverter low cut off goes off before the battery. This way ur whole system will not shut down and u can still solar charge the battery. Hope this helps.. good luck

 

[woodlecj]

Thanks for the responses. I guess one of my points being if it's a 100A BMS, shouldn't it have tripped? 128A for 10 minutes seems like a long enough time for a BMS to figure out over it's current. I just wonder if the BMS is no good (it is a Chinese battery after all). If I add another like battery in parallel, that would give me 200A; right? Also what OCPDs do you folks like?

 

[John Frum]

Thanks for the responses. I guess one of my points being if it's a 100A BMS, shouldn't it have tripped? 128A for 10 minutes seems like a long enough time for a BMS to figure out over it's current. I just wonder if the BMS is no good (it is a Chinese battery after all). If I add another like battery in parallel, that would give me 200A; right? Also what OCPDs do you folks like?

Assuming that was for me, It varies by BMS.
Which battery do you have?

 

[John Frum]

I just wonder if the BMS is no good (it is a Chinese battery after all). If I add another like battery in parallel, that would give me 200A; right?

Good idea

Also what OCPDs do you folks like?

for 12 volt LFP I like MRBF fuses.

P: MRBF-Series: 1646: Search: mrbf

mrbf

www.waytekwire.com

 

[woodlecj]

Shentec bought on Amazon. Seems decent so far.

https://www.amazon.com/Shentec-Rechargeable-Overland-Off-Grid-Application/dp/B0B4SFJT1C/ref=sw_img_rp_a_ewe_4_wdg_289_2?_encoding=UTF8&pd_rd_i=B0B4SFJT1C&pd_rd_w=oTIrC&content-id=amzn1.sym.1d2557e2-42a2-47c9-9ca0-efcedaefbe26&pf_rd_p=1d2557e2-42a2-47c9-9ca0-efcedaefbe26&pf_rd_r=NJNWXQ7G1KCHGAGH18NS&pd_rd_wg=cPXA5&pd_rd_r=3528f5ec-2896-40cb-8b4d-c06977124c4b

 

[John Frum]

Shentec bought on Amazon. Seems decent so far.

https://www.amazon.com/Shentec-Rechargeable-Overland-Off-Grid-Application/dp/B0B4SFJT1C/ref=sw_img_rp_a_ewe_4_wdg_289_2?_encoding=UTF8&pd_rd_i=B0B4SFJT1C&pd_rd_w=oTIrC&content-id=amzn1.sym.1d2557e2-42a2-47c9-9ca0-efcedaefbe26&pf_rd_p=1d2557e2-42a2-47c9-9ca0-efcedaefbe26&pf_rd_r=NJNWXQ7G1KCHGAGH18NS&pd_rd_wg=cPXA5&pd_rd_r=3528f5ec-2896-40cb-8b4d-c06977124c4b

Never heard of that one.

 

[woodlecj]

Well, there's a million of 'em! A lot of them seem similar as I've watched Will and others tear them apart.

 

[John Frum]

Suggest you get batteries with a smart bms.
That way you can see what is going on with the cell balance.
Also you won't need a shunt if you have smart bms.

 

[Bud Martin]

You should ask the seller for the full spec of the BMS, according to the web page, it shows 300A/10s board, not sure what that means.
The used SOK12V 100Ah I bought has cutoff current of 330A!

 

[John Frum]

You should ask the seller for the full spec of the BMS, according to the web page, it shows 300A/10s board, not sure what that means.
The used SOK12V 100Ah I bought has cutoff current of 330A!

I see 200 amps for 3 seconds.
330 amps is probably considered short circuit current.
I doubt that BMS would survive long at ~150 amps.

 

[woodlecj]

Well it seems like people love the SOK batts. And if the specs are similar on both, isn't the BMS over spec'd for both?

 

[John Frum]

Well it seems like people love the SOK batts. And if the specs are similar on both, isn't the BMS over spec'd for both?

No