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Tinker

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Joined: 07/11/2007
Location: Australia
Posts: 1904

Posted: 10:33pm 16 Jul 2016

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I have a 48V/200Ah lithium (LYP) battery bank. I built my own BMS for it which works well. For low cell voltage disconnect there are two 80A latching relays in parallel.

So, how about in stead of using the 80A relays, shutting the inverter down via a small relay that duplicates the inverters ON/OFF switch? This would be quite easy to do with my set up.

The advantage is that its completely automatic. Detecting a low cell voltage the inverter would shut down, removing the load on the battery bank.
Now, as soon as the cells are recharged sufficiently (via solar), to a level a bit above the shut down value the inverter would soft start and power the load again.

Doable?
Crazy idea?

Klaus

fillm

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Joined: 10/02/2007
Location: Australia
Posts: 730

Posted: 12:19am 17 Jul 2016

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Hi Klaus,

No that's not a crazy Idea, I have Latronics program the LV Cut outs to suit lithium and it cuts out as below. There is a choice of 4 settings with 2 dip switches then it does not reconnect until the cells will reach a charge voltage. They are fairly conservative and capable of giving good DOD without damage.

SW pos1- Low Voltage Cut out 49.(3.06V)Re-Connect 51.SW 5 - ON / SW6 - ON

SW pos2- Low Voltage Cut out 50 (3.12)Re-Connect 52 .SW 5 - OFF / SW6 - OFF

SW pos3- Low Voltage Cut out 50.5(3.15)Re-Connect 52.5 SW 5 - ON /SW6 - OFF

SW pos4- Low Voltage Cut out 49 (3.06)Re-Connect 53 ..SW 5 - OFF /SW6 - ON

PhillM ...Oz Wind Engineering..Wind Turbine Kits 500W - 5000W ~ F&P Dual Kits ~ GOE222Blades- Voltage Control Parts ------- Tower kits

gpalterpower

Senior Member

Joined: 19/07/2009
Location: Australia
Posts: 175

Posted: 11:32pm 17 Jul 2016

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HI Guys,
I have a similar setup on my system at home. I purchased one of those cheap power star inverters about a year ago. Its been reliable powering my home and small workshop every...single...day without a hickup. The only drawback is that it consumes 110w on standby. so I decided to attach as little power saving device so it shuts down when the battery voltage is low

I live on grid/off grid. Off grid in the morning when the sun comes up and on grid after the sun goes down. I have a small battery bank but with more solar panels, some more batteries and if I can convince the the kids to turn off the lights and TV when not being used, I will be able to go off grid permanently.

I have a dual contactor setup for the changeover, so only one contactor can be electrically energised and mechanically locked at a time. This ensures that there is NO chance of cross over to the main grid. That is a definate NO NO!!! Its energised by a small relay which in turn is activated by a volt detect relay

I purchased a programmable volt detect relay thru ebay. Bypassed the main switch on the inverter thru a small relay and in turn is activated by the volt detect relay thru a timer, which was added to the equation to give the inverter a 10 sec head start to turn on. That way there would be full power when the change over occurs. Another stay-on relay was fitted so the inverter stays on for 10 sec after shutdown.

Timer near centre and the volt relay is above and to the right. I programmed it to switch on a 27.6v and off at 24.4v . Been working perfectly for 6 months now.

Marcus

if it aint broke dont fix it!!

Madness

Guru

Joined: 08/10/2011
Location: Australia
Posts: 2498

Posted: 11:37pm 17 Jul 2016

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Have you seen the fix to reduce the idle current of that inverter here.
https://forums.energymatters.com.au/solar-wind-gear/topic3344.html

There are only 10 types of people in the world: those who understand binary, and those who don't.

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