Low Voltage Disconnect for pump on 24V system.

[mungewell]

Hi all,

I'm busy build my system, and am at the 'water pump stage'. I am intending to use a DC pump as I understand that they are much more efficient, but I'd like to include a low voltage disconnect to prevent damage to battery pack in the case of deep discharge.

1). Any one know of a good source?

The ones that I have found so far seem to be of the relay type (for lower currents, I want to switch 15A max) and these obviously draw a certain amount of current to keep the thing energised (24/7!).

2). Am I being paranoid about phantom loads?

Also the one that I have seen seems to have a high disconnect voltage (25V), which looking at the idle voltage/SoC tables appears to be around 80% charged/20% discharged.

3). Isn't the voltage of an 'in use' battery likely to be lower than this, and what set point would people suggest for say 60% charge/40%discharge?

I would probably set this a little higher than than the inverter as 'no-water' is more pleasant than 'defrosted freezer', and is a good indication to wife/kids that all is not well in DC land ;-)

Cheers,

Simon.

[ghurd]

I have a circuit (and kit) that would work, with a bit of reworking.  The current to keep it energized is about 10~15ma.  

It has no over voltage disconnect, although a second kit with reworking could provide that feature.

The 24V version of the kit is being tested for glitches as time permits.  It is a slow going process.

An `in use' 24V battery could pass 30V on occasion.

G-

[mungewell]

> An `in use' 24V battery could pass 30V on occasion.

I was thinking more about the drop in voltage from discharging cells under load in the middle of the night.

Although I hadn't thought to ask about the maximum allowable voltage, better phone the supplier....

Simon.

[SamoaPower]

I think you want a Trace/Xantrex C40 controller. Both low voltage disconnect and reconnect points are adjustable and works on 12,24 and 48V systems. It handles 40A and uses no relays.

[electronbaby]

the c-40 charge controllers will use PWM on the output. For use with an external relay, you have to filter out the PWM waveform with some caps. It is do-able.

[mungewell]

Wow, what a good suggestion! - didn't even occur to me that these can be used as a load controller which offers output/battery protection with a min->max voltage range.

Price isn't too bad either. My 'pet' dealer (who's getting far too much of my money of late) has the C-35 for CDN 125.00

Thanks,

Simon.

[SamoaPower]

Roy,

In the load control mode, the C40 doesn't use PWM (not needed). Also no need to drive a relay. The C40 has three modes of operation, series for PV, diversion for PV, wind or hydro and load control.

73 de AH8A

[electronbaby]

oh ok. my bad. Ive never used that controller in that mode. Ive always used dedicated circuits. I have had very bad luck with those controllers. I have tried to swap out everyone I have. the old trace units work well. I think xantrex had some QC issues when they took over possibly. I now run all mx60's. They have a dedicated aux relay that you can change the bias of within the firmware. Im sure your aware. :-)

[mungewell]

Just to follow up on this, I did indeed purchase a C35 for doing low voltage disconnect - lets hope it never actually has to trip out.

I was a little wrong in it's operation, there are two dials to set disconnect voltage and restore voltage. It does not do overvoltage protection.

It's hooked in to the DC side of my outback system, and provides a bus-bar of power to the DC loads (only my pump at the moment).

See my image files for pictures.... http://www.otherpower.com/images/scimages/2645/panel.JPG

Cheers,

Simon.

[mungewell]

Just a friendly reminder to me and all with DC applicances.... Remember to isolate the loads when performing battery equalisation.

Simon.