12V Low Voltage Disconnect (LVD) capable of switching 300W inverter?

[createthis]

Hello,

I'm thinking of buying a 300W pure sine wave inverter for my little portable solar system (basically, it's a Yeti 400 with a blown AC inverter and a 200W solar panel).

I'll have to run this guy from the anderson 45W chaining connectors on the side of the Yeti 400. Anytime I do this, I like to have a low voltage disconnect (LVD) inline to protect the battery. See this video for details of how I did this for my 12V fridge:

https://youtu.be/O_DnUwPpbKQ

The inverter will draw considerably more amps than my fridge, so I'm trying to figure out how to scale up the APO3 LVD idea to 60 amps or so. Unfortunately, my initial google searches didn't reveal a clear ready-made product available to do this.

Yes, the inverter I'm looking at has an automatic shutoff at 10V, but my battery would already be trashed that low. I'm thinking something in the 12.3 to 12.6V range would be better for my purposes.

Any ideas?

[jakesz28]

I did not watch the whole video but if you like your current low voltage cut off, I would just add a 60 amp ssr in your load circuit. You can use your current low voltage cut off to control the solid state relay. Or you can use a standard 60 amp relay/contactor but the coil would add a load to the circuit.

[inetdog]

I did not watch the whole video but if you like your current low voltage cut off, I would just add a 60 amp ssr in your load circuit. You can use your current low voltage cut off to control the solid state relay. Or you can use a standard 60 amp relay/contactor but the coil would add a load to the circuit.

I would have a slight concern whether the LVCO solid state relay will work with only the load of an SSR attached to it. Chances are it will work fine, but if not a small indicator bulb would probably draw enough current.

[lkruper]

Hello,

I'm thinking of buying a 300W pure sine wave inverter for my little portable solar system (basically, it's a Yeti 400 with a blown AC inverter and a 200W solar panel).

I'll have to run this guy from the anderson 45W chaining connectors on the side of the Yeti 400. Anytime I do this, I like to have a low voltage disconnect (LVD) inline to protect the battery. See this video for details of how I did this for my 12V fridge: https://youtu.be/O_DnUwPpbKQ

The inverter will draw considerably more amps than my fridge, so I'm trying to figure out how to scale up the APO3 LVD idea to 60 amps or so. Unfortunately, my initial google searches didn't reveal a clear ready-made product available to do this.

Yes, the inverter I'm looking at has an automatic shutoff at 10V, but my battery would already be trashed that low. I'm thinking something in the 12.3 to 12.6V range would be better for my purposes.

Any ideas?

Samlex makes them. Here is a 60 amp one. I have also seen 40 amp and 200 amp.

http://www.amazon.com/Samlex-Battery-Guard-RoHS-Compliant/dp/B00NM57BQG/ref=sr_1_6?ie=UTF8&qid=1444865590&sr=8-6&keywords=samlex+battery+disconnect

[createthis]

Samlex makes them. Here is a 60 amp one. I have also seen 40 amp and 200 amp.

http://www.amazon.com/Samlex-Battery...ery+disconnect

That might work. The highest voltage threshold it allows, according to the user manual, is 12V, which, according to this AGM state of charge table, is 25% remaining capacity: http://www.energymatters.com.au/comp...age-discharge/

That's definitely better than the automatic disconnect on the inverter. I like that it uses mosfets rather than relays too. I just wish it had higher voltage set points so I could target 75% or so.

[lkruper]

That might work. The highest voltage threshold it allows, according to the user manual, is 12V, which, according to this AGM state of charge table, is 25% remaining capacity: http://www.energymatters.com.au/comp...age-discharge/

That's definitely better than the automatic disconnect on the inverter. I like that it uses mosfets rather than relays too. I just wish it had higher voltage set points so I could target 75% or so.

I had read that it had 10 set points. It is odd that 25% SOC is the highest.

[createthis]

I had read that it had 10 set points. It is odd that 25% SOC is the highest.

Indeed. Here's the table from the Samlex BG60 user manual:





Here's the AGM SOC table:

[lkruper]

Indeed. Here's the table from the Samlex BG60 user manual:





Here's the AGM SOC table:

I suppose that for float service and occasional emergency usage that 25% SOC works well enough. For cycling the goal would be to have the load sized so that discharge does not happen below the SOC of 50% or higher and only use the disconnect to save the batteries when something unusual happens, like > 5 days of clouds, etc.

[createthis]

I suppose that for float service and occasional emergency usage that 25% SOC works well enough. For cycling the goal would be to have the load sized so that discharge does not happen below the SOC of 50% or higher and only use the disconnect to save the batteries when something unusual happens, like > 5 days of clouds, etc.

Agreed. 25% is definitely better than nothing or 0%.

[createthis]

So, my 300W inverter arrived. I was testing it last night and I think I found out why Samlex doesn't offer a higher voltage set point in it's LVD. Voltage sag. Under a 180W load, my AGM battery sagged to about 12.3V after about 10 seconds of run time. Removing the load saw the voltage rise back up to say 13.2V after 30 seconds or so. Now I understand why amp hour meters cost so much. Voltage is a useless measure of state of charge unless the system has been idle for about an hour.

[inetdog]

Voltage is a useless measure of state of charge unless the system has been idle for about an hour.

You have made an important realization! You also want to wait a few hours after charging too.

But all is not lost. If you are willing to take the time to run a lot of tests, you will be able to build a table of SOC versus voltage for several values of discharge and charge current. (Measure resting voltage, try different loads and measure working voltage, rest and measure again. Repeat for charging currents.)
That is still not as good a Specific Gravity for determining SOC, but since you have AGM batteries it will be the best you can do.

[PNjunction]

For small stuff like this, if you aren't pulling more than 35A, you may want to look into these LVD's aimed primarily at the lead-acid emergency vehicle market:

http://www.powerwerx.com/emergency-vehicle/dc-automotive-timer-lvd-battery-guard.html

Either the ITS-12 or perhaps the LVD35 might do the trick. Both have a hard-set LVD, in addition to a *timed* lvd which is voltage selectable. The timed lvd is handy, and I shoehorn that feature into place for my lifepo4's.

Check the manuals online, and see if the hard lvd and the user selectable timed-lvd voltages might be a better fit.

[lkruper]

For small stuff like this, if you aren't pulling more than 35A, you may want to look into these LVD's aimed primarily at the lead-acid emergency vehicle market:

http://www.powerwerx.com/emergency-vehicle/dc-automotive-timer-lvd-battery-guard.html

Either the ITS-12 or perhaps the LVD35 might do the trick. Both have a hard-set LVD, in addition to a *timed* lvd which is voltage selectable. The timed lvd is handy, and I shoehorn that feature into place for my lifepo4's.

Check the manuals online, and see if the hard lvd and the user selectable timed-lvd voltages might be a better fit.

That is pretty cool. The one thing I cannot figure out is any rhyme or reason for the LVD settings associated with the timed events. For example, there is an 11.0 at 30m bracketed by 11.4 for both 15 min and 1 hour. It looks like both conditions must be met, both the timed event and the LVD setting, is that correct? That way voltage sag is not a major issue?

[PNjunction]

Ah yes, it can be slightly confusing with those docs with the two unrelated columns next to each other.

The *timed* event for the ITS-12 starts roughly at 12.8v, and you choose the time based on the first column and set the switch accordingly.

The hard-lvd, is either 11.0 or 11.4v.

So the user decides what is the best combination for their style of operations.

In MY case, the timed event starting at 12.8v was very fortunate, since that is about 80% DOD for a 12v lifepo4. Lightly loaded, ie about .2 - .3C, the timed event will occur BEFORE the 11.x volt hard limit - which for me is too low for lifepo4, but better than nothing.

So yes, this lvd is smart enough to deal with voltage sag from a huge load which hits the hard lvd first, or a light load (like dome lights left on, or radios in receive only mode etc) will trigger the timed event at a higher voltage sooner.

The reason for setting a timed event which starts at 12.8v would be primarily for say an emergency vehicle leaving all their gear running and still needing to be able to start the vehicle. If the only thing it had was the low 11.xV hard limit, once you reached that point, you may not be able to start the vehicle, although you have saved the battery.

The APS-12 only has a timed lvd starting at 12.6v. (some units were 12.8v) 25A max
The ITS-12 is the smartest having both the timed (starting at 12.8v) and a hard lvd. This is what I currently use for lifepo4 set for the shortest timeout.
The APS-35 only has a hard-lvd, but one can set the voltage anywhere from 10.6 to 12.2v. Set too low, and you'll save the battery but possibly not start the vehicle.

Obviously designed for lead-acid, but for small-scale "pack level" lvd's with lifepo4, one could shoehorn these into service - but not for the guy next door.

[lkruper]

Ah yes, it can be slightly confusing with those docs with the two unrelated columns next to each other.

The *timed* event for the ITS-12 starts roughly at 12.8v, and you choose the time based on the first column and set the switch accordingly.

The hard-lvd, is either 11.0 or 11.4v.

So the user decides what is the best combination for their style of operations.

In MY case, the timed event starting at 12.8v was very fortunate, since that is about 80% DOD for a 12v lifepo4. Lightly loaded, ie about .2 - .3C, the timed event will occur BEFORE the 11.x volt hard limit - which for me is too low for lifepo4, but better than nothing.

So yes, this lvd is smart enough to deal with voltage sag from a huge load which hits the hard lvd first, or a light load (like dome lights left on, or radios in receive only mode etc) will trigger the timed event at a higher voltage sooner.

The reason for setting a timed event which starts at 12.8v would be primarily for say an emergency vehicle leaving all their gear running and still needing to be able to start the vehicle. If the only thing it had was the low 11.xV hard limit, once you reached that point, you may not be able to start the vehicle, although you have saved the battery.

The APS-12 only has a timed lvd starting at 12.6v. (some units were 12.8v) 25A max
The ITS-12 is the smartest having both the timed (starting at 12.8v) and a hard lvd. This is what I currently use for lifepo4 set for the shortest timeout.
The APS-35 only has a hard-lvd, but one can set the voltage anywhere from 10.6 to 12.2v. Set too low, and you'll save the battery but possibly not start the vehicle.

Obviously designed for lead-acid, but for small-scale "pack level" lvd's with lifepo4, one could shoehorn these into service - but not for the guy next door.

Thanks, so if I understand you, one can either pick a particular time with an associated LVD, an LVD with an associated time, but not each independently.