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modual that monitors the output of a bms??
#1
hello
wonder if there is such a modual or pcb that i could use to monitor the output of a bms so when it is on it just detects voltage then does something like 5v, which i could then switch a contactor or relay, i want to get a cheep bluetooth bms say that switches 20amps, and use that output to switch a larger output like a contactor? i want to get one of those cheep chinese bluetooth bms for an electric skateboard
hope that makes sennse
thanks
Battery is li iron using 18650s, 14s, 0p, and growing cell so far 300, untesteded.
Bms is a diy open source by stuartpittaway.
No solar yet, 
Building wind turbine, 48v im after a 48v motor if anybody has one for sale.
Cells 2000 to 2500ma.
Cells 1500 to 2000ma.
Cells 1000 to 1500ma.
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#2
A proper BMS do it for you.

But what I expect you want is to triger something else externally? Can you describe what you want to trigger and with what?
It sounds like an extra relay but how to trigger that depends on the output you have
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#3
Why not use the output of the cheap BMS (eg the 20A output) to drive the external contactor coil directly?
If you find the right contactor, they only need a pulse to switch states, eg the gigavac ones at evparts or similar.
Running off solar, DIY & electronics fan :-)
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#4
i was thinking of trying to turn on a relay or contactor or an ssr? and i need to drive something capable of running 100a pluss dc.
i was thinking maby using a voltage devider to reduce the voltage a bit to drive a ssr, 30 v but the voltage will vary as the output from the bms varys due to the battery going down
Battery is li iron using 18650s, 14s, 0p, and growing cell so far 300, untesteded.
Bms is a diy open source by stuartpittaway.
No solar yet, 
Building wind turbine, 48v im after a 48v motor if anybody has one for sale.
Cells 2000 to 2500ma.
Cells 1500 to 2000ma.
Cells 1000 to 1500ma.
Reply
#5
When to trigger it?

A proper BMS do have such outputs. Batrium is even configurable so you can set up when to trigger and why
The Ultimate DIY Solar and build place
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcoming: 14S 18650~30kWh | Automatic trip breakers, and alot more
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#6
(10-27-2019, 07:33 PM)Jonisingt35r Wrote: i was thinking of trying to turn on a relay or contactor or an ssr? and i need to drive something capable of running 100a plus dc.
i was thinking maybe using a voltage divider to reduce the voltage a bit to drive a ssr, 30 v but the voltage will vary as the output from the bms varys due to the battery going down

An SSR won't care much about the voltage as long as it's always within the specs for the input. You could just use a resistor divider.
Just make sure the SSR only sees voltage that's in-spec for it's input.  Allow for the lower battery voltage under heavy load or it might cut in/out. 

Your notes suggest a 48V system, so for step down something like a golf cart voltage reducer module (ie rated for 40V to 60V input, 12V output) like found on aliexpress from "daygreen" like this: 
http://s.click.aliexpress.com/e/MlBqMnmg
or similar 10A one would work well for driving an SSR.
If driving a contactor, get select one to suit the contactor's coil.
I'd put a 5W, 2.2ohm resistor & a fuse in series with the input (resistor to limit in-rush current).

The daygreen units are great for providing a 12V supply to other electronics too.

Like daromer says, there's other functions that the better BMS's can do.
Running off solar, DIY & electronics fan :-)
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#7
If you go the SSR route make sure you have proper sinking. Those suckers get hot! I use them on my electric brewing setup (switching 26 amps of 240vac) and with a giant heat sink, good contact and high-end thermal paste I still need to run a cooling fan to pull air across the heat sink.
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#8
Depending on the tech they use in DC SSR's they might not get so hot - but good point re the heat.
The AC ones use triacs/thyristors which doo run hot.
If the DC ones use FETs they might run cool. Suspect they use IGBT's which get warm.
Running off solar, DIY & electronics fan :-)
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#9
Good to know! I hadn't thought about a different trigger/coupling device. Victron uses FETs in their battery protect devices. Those can switch some pretty big loads and don't have functionality for heat sinking built in. Must not be too much of a problem.
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#10
So it seems there's quite a few different types of DC SSR
http://www.crydom.com/en/products/panel-...dc-output/

A quick test would verify internal devices in an SSR:
- switch it on with the specified input voltage
- run a small load say 1A (whatever is handy, load doesn't matter exactly)
- use a multimeter to measure the voltage across the output terminals
From the crydom data sheets, the MOSFET ones drop ~.6V, the Bipolar ones drop ~1.1V, the IGBT ones drop ~1.5V

Not sure why you wouldn't just use a bank of MOSFETS driven with the right voltage to the gate? next to zero drop because the output drive circuit isn't powered by the load like it is in DC SSR's
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