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Old 31-05-2019, 18:43   #91
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Re: Are these cheap lithiums ok to use??

I don’t like the cheap so called ‘drop-in’ lithium batteries with built-in BMS. I prefer to be able to measure each cells voltage to check what’s happening. I also like to have a replaceable BMS and relay rather than have it sealed within battery. The internal mosfet type relay cannot carry the same current as a mechanical contractor and that is why the charge/discharge currents are so low. If several of these cheap lithium batteries are paralleled to provide the current required for a big inverter you create a few extra problems. If for any reason one of the batteries BMS trips, all the current has to be provided by the remaining batteries which further loads up the remaining relays.
My Winstone LiFePo4 cells on the boat are now over 9 years old and still perform great. I have just put a set of CALB cells with external Zeva BMS in the camper. I tried solid state relays with this new installation and have now gone through two relays under warranty. They cannot handle the loads. I am reverting back to the old style contactor. If it was integrated in the sealed battery then the whole battery would have to be replaced.
In my opinion individual cells with external BMS & relay is the way to go.
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Old 01-06-2019, 10:36   #92
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Re: Are these cheap lithiums ok to use??

+1
always better to have full control of the cells and design the system to your needs.
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Old 01-06-2019, 12:54   #93
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Re: Are these cheap lithiums ok to use??

9 years? That could be our first report from a long-term user!

Solid state relays is just a marketing word, that's a MOSFET transistor doing the switching. Which has some reasons and purposes, but the dumb old solenoid relays just aren't as sensitive as electronics are. Although, since they no longer make relays with mercury-wetted contacts, relays have a life limited by the quality of the contacts they are using. Always a trade-off.

The drop-ins make sense for the user who only needs one, and doesn't want to be bothered with setting up or matching outboard electronics.
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Old 01-06-2019, 19:49   #94
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Re: Are these cheap lithiums ok to use??

Quote:
Originally Posted by hellosailor View Post
9 years? That could be our first report from a long-term user!

Solid state relays is just a marketing word, that's a MOSFET transistor doing the switching. Which has some reasons and purposes, but the dumb old solenoid relays just aren't as sensitive as electronics are. Although, since they no longer make relays with mercury-wetted contacts, relays have a life limited by the quality of the contacts they are using. Always a trade-off.

The drop-ins make sense for the user who only needs one, and doesn't want to be bothered with setting up or matching outboard electronics.
I think the MOSFET (solid state) relays are ok if you battery setup is just to run light loads but as soon as you run inverters for coffee machines, AC and hot water the mechanical relays are better for high current use. Itís cheap to carry a spare and easy to replace when external from the battery bank.
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Old 01-06-2019, 19:54   #95
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Re: Are these cheap lithiums ok to use??

Quote:
Originally Posted by Seawindcruiser View Post
I think the MOSFET (solid state) relays are ok if you battery setup is just to run light loads but as soon as you run inverters for coffee machines, AC and hot water the mechanical relays are better for high current use. Itís cheap to carry a spare and easy to replace when external from the battery bank.
not exactly .
If the mosfets can't adequately handle your inverter usage then you undersized the bms .
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Old 01-06-2019, 21:31   #96
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Re: Are these cheap lithiums ok to use??

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not exactly .
If the mosfets can't adequately handle your inverter usage then you undersized the bms .
I was referring to MOSFETs that are seperate to the BMS. The BMS only activates the Solid state relay/s.
I go back to my original point that a lot of the Ďdrop-iní replacement LiFePo4 batteries that have inbuilt BMS and relays are not rated for heavy inverter (or big charger) use.
Furthermore, if they are sealed they canít be repaired or replaced easily. In my opinion an external BMS and seperate conventional contactor/relay (std or latching) is better for live-aboard use.
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