Battery Discharge Protection

Submitted: Monday, Nov 28, 2011 at 07:53

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lesterb

Can someone give me some advice on battery discharge protection. I've destroyed my deep cycle battery because something has been left on in the caravan and the battery has fully discharged and now it won't hold a charge.
I don't have solar panels at the moment but the anti-discharge part of the solar regulators looks to be the answe.
Can I connect one of these without solar panels just to prevent over discharging the battery?
If so, where do I connect my battery charger, the solar panel input or straight across the battery?

Lester

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Reply By: Member - Frank P (NSW) - Monday, Nov 28, 2011 at 08:08

Monday, Nov 28, 2011 at 08:08

You could use something like this.

There are other brands as well.

Cheers

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Follow Up By: lesterb - Monday, Nov 28, 2011 at 08:18

Monday, Nov 28, 2011 at 08:18

Thanks for your input but this link doesn't work.
Can you provide another link?

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Follow Up By: lesterb - Monday, Nov 28, 2011 at 08:20

Monday, Nov 28, 2011 at 08:20

Sorry, it did work. It came up with a message about bad request but it did open the web page.

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Follow Up By: Racey - Monday, Nov 28, 2011 at 09:17

Monday, Nov 28, 2011 at 09:17

It worked for me. If you are having trouble go direct to the REDARC website direct at www.redarc.com.au Redarc

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Reply By: Cobsy - Monday, Nov 28, 2011 at 11:36

Monday, Nov 28, 2011 at 11:36

Gday,

You could use a low voltage cut out device which can be set to different voltages ie: 10.5, 11.5 etc. I think ABR sidewinder has them for about $80 on ebay

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Follow Up By: ABR - SIDEWINDER - Monday, Nov 28, 2011 at 13:47

Monday, Nov 28, 2011 at 13:47

Hi Lesterb

Here is the pdf file for the 12V 60A unit. 12V-60A-Unit

Regards

Derek from ABR

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Follow Up By: ABR - SIDEWINDER - Monday, Nov 28, 2011 at 13:49

Monday, Nov 28, 2011 at 13:49

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Follow Up By: lesterb - Sunday, Dec 11, 2011 at 08:19

Sunday, Dec 11, 2011 at 08:19

I've found another similar device that may be of interest to members.
Projecta Intelli-Volt

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Reply By: Dennis Ellery - Monday, Nov 28, 2011 at 12:02

Monday, Nov 28, 2011 at 12:02

I use a couple of these for similar purposes – about $70 from the 12volt shop (12volt.com.au)
The ARRID Auxiliary Voltage Controller (AVC) is a small yet powerful device that is used to prevent damage to low voltage appliances (including fridges, halogen globes or televisions) from both high and low voltage. The ARRID AVC will also prevent excessive discharge of batteries, and is available in a higher voltage version for starting batteries (11.8 V DC cutout) or a deep cycle model that allows deeper battery discharge (10.8 V DC cutout). The ARRID AVC will disconnect DC loads when the battery voltage exceeds 16 V DC.
The ARRID AVC has a maximum rating of 25 amps, but will actually cope with higher inductive loads than many similarly rated discharge protection devices.
This is because the ARRID AVC features a 60 second time delay between reaching the designated cut off voltage and disconnecting the load. The AVC will not disconnect the load due to short decreases in voltage caused by the high start-up currents of inductive loads, (eg. compressor refrigerators). This feature eliminates the annoying “chatter” effect that may occur with low voltage cutouts that do not have this feature. Voltages can be adjusted for specific requirements. For further information and specifications contact ARRID.

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Follow Up By: Dennis Ellery - Monday, Nov 28, 2011 at 12:16

Monday, Nov 28, 2011 at 12:16

I should have also noted that devices such as these (that use a mechanical relay) do cause another problem. Some draw up to 250 milliamp (1/4 amp) when in use. This means that if you leave the device connected for a long period of time, it will flatten the battery to its predetermined cuttout voltage.

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Follow Up By: Member - Frank P (NSW) - Tuesday, Nov 29, 2011 at 10:36

Tuesday, Nov 29, 2011 at 10:36

Yes, my off-road caravan manufacturer used a customised Redarc SBI as a low-voltage cutout. Right idea, wrong product for the job as it drew half an amp or more to remain "on". Would readily flatten the battery in storage, then switch off, thereby protecting the battery that it had flattened!!!

I have replaced that with a solid state relay that needs only 3 milliamps to remain latched on - that's about equal to the self-discharge rate of a lead-acid battery.

Point being, a conventional relay WILL draw current, but you are not limited to convention. The solid state option is better, and you can get them in big capacities.Mine is 100 amp, from Jaycar.

I don't know what technology the Redarc unit I linked to elsewhere in this topic uses.

Cheers

Frank

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Follow Up By: Dennis Ellery - Tuesday, Nov 29, 2011 at 10:49

Tuesday, Nov 29, 2011 at 10:49

Thanks for the tip Frank,
That makes excellent engineering sense.
It makes you wonder why the manufactures of Voltage Cutoff Relays don't do it in the first place.
I intend to run a couple of fridges through it, about 10 amps at the most - do you think your 100 amp Jaycar will handle that without a heat sink?
Regards Dennis

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Follow Up By: Member - Frank P (NSW) - Tuesday, Nov 29, 2011 at 16:31

Tuesday, Nov 29, 2011 at 16:31

You're welcome, Dennis.

You'll have no problem with 10 amps through the 100 amp SS relay without a heatsink, though I suppose if you can mount it on something metal, like a bit of camper framework, that would be best. The relay I use is about 50mm square, 15mm thick, looks like epoxy or plastic. I have it mounted on a bit of aluminium frame in my Karavan, 3mm thick, 30 wide. No problems with 30 amps going through it. I don't think it even gets warm.

You'll need some kind of voltage sensing device to drive it, as by itself it doesn't sense voltage. I'm sure there are kits or chips out there. Find one that suits your desired drop-out voltage.Mine is 10.8V which is the 5% state of charge, or 95% discharge of my AGM batteries, controlled by my DC-DC smart charger which has a low voltage cutout output, but a chip or a kit could achieve the same thing. (I'm not sure about 10.8V - I think I would like it higher, about 11.2V - I might be able to get a custom mod for that)

In total, about 8mA to stay latched on.

Here's a link to a self-contained unit that draws 15mA, but the cut-out is too high for my money - 11.9V is a touch more than 50% discharge for AGM, so too early in my opinion.

Cheers

Frank

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Follow Up By: Dennis Ellery - Wednesday, Nov 30, 2011 at 11:51

Wednesday, Nov 30, 2011 at 11:51

Thanks Frank,
I will modify one of my Arrid voltage controlers and replace the 25amp mechanical relay. These have a pot inside that varies the trip points.
Regards Dennis

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Reply By: Nomadic Navara - Monday, Nov 28, 2011 at 12:28

Monday, Nov 28, 2011 at 12:28

If you are intending to add solar panels in the future then don't waste your money on an interim solution. Go straight to your chosen solar regulator. Mount it where you can observe it if it has metering on the front. You do not have to alter the battery charger wiring, the two will work in parallel.

Run heavy cabling up to the controller from the battery and then back to the distribution fuses. Use at least 6 square mm cable (not 6mm auto cable which only has 4.8 squ mm of copper in it.) If you have an inverter wired to your battery you have a couple of alternatives. If the load capacity of the regulator will accommodate the inverter load then use much heavier cabling and run it through the protection of the controller. If not then connect the inverter directly to the battery and be careful you don't forget to switch it off when not in use.

If there is provision for external sensing of the battery voltage run smaller wires for this direct from the battery terminals to the controller external sensing terminals. If there is battery temperature sensing available, run that in as part of your initial installation. Everything will be ready to roll when you add the panels. You could also run the cables for the panels up to the place where you will eventually penetrate the roof at this time. Where cabling is exposed you can get small ducting with snap on lids from the usual suspects like Bunnings and electrical wholesalers.

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Follow Up By: lesterb - Monday, Nov 28, 2011 at 12:57

Monday, Nov 28, 2011 at 12:57

Thanks PeterD this is exactly the confirmation I was looking for. I too am a retired radio and electronics technician with very little experience in 12 volt systems. Started my working life as an apprentice radio tradesman (the word electronics was hardly heard of in those days) but progressed to computers and spent the last 10 years of my working life as a local area network administrator.
I'm thinking of a 20A solar regulator off ebay. I had a 10A version with a 10W solar panel and small sla battery in my old van just for auxiliary/emergency led lights and it worked well.

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Follow Up By: Battery Value Pty Ltd - Monday, Nov 28, 2011 at 13:58

Monday, Nov 28, 2011 at 13:58

Hi Peter,

if you do get a solar regulator with the electronic switch in it, just be aware that a great majority of them are switching the negative.

So if your load has a connection to chassis negative, and the deep cycle battery also, then this electronic switch would need to be in the positive leg, otherwise it would get bypassed by the chassis negative current path.

Our MPPT solar regulators do have the switch in the positive, but are limited to 10A continuous/35A peak.
For higher output currents, you could utilise a relay.
A relay would also make a negative switched regulator useful by providing the necessary isolation function by breaking this chassis negative bypass.
Of course relays do have significant self consumption as has been mentioned earlier.

cheers, Peter

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Follow Up By: Nomadic Navara - Monday, Nov 28, 2011 at 16:24

Monday, Nov 28, 2011 at 16:24

Good point Peter.

Lester - What peter was referring to is the Plasmatronics and Steca type controllers. They were designed for the communications industry that uses positive earth systems. They are more difficult to use than ones designed for negative earth systems. The negative terminals for the panels, battery and load are all at slightly different potentials, you can only earth one of them or you will upset the operation of the controller.

If you are getting a Plasmatronics controller do not get one of the PL series. Get yourself the Dingo model - These are similar to the PL series but have been re-designed for negative earth systems.

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Reply By: Ross M - Monday, Nov 28, 2011 at 21:12

Monday, Nov 28, 2011 at 21:12

You mentioned the battery went flat. I am a bit unclear as to the real problem.
If this flattening of the deep cycle happened over a period of time it is possible the radio unit or similar has been left connected to the battery and caused the discharge. Is it possible there is nothing wrong at all except the slow but sure discharge of the entertainment devices keeping their memories alive.
With batt charged you can check with a LED and 600ohm resistor between batt terminal and lead. If it lights there is flow out of your battery. Neg lead is ok to check.
Probably best to switch off the main battery lead or disconnect it if leaving the gear unused for a while. Always disconnect neg lead first in all batt operations to be safe.
Regards Ross M

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Follow Up By: lesterb - Tuesday, Nov 29, 2011 at 08:06

Tuesday, Nov 29, 2011 at 08:06

Hi Ross,

My battery is not just flat it's had it.
Reason for arriving at this conclusion are;
Battery voltage 2.6v when problem discovered.
Extreme battery heating during charge.
Sulphur smell during charge.
Battery now drops back to 0v after charger remove.
At around $200 for a battery I'm putting in a solar regulator with discharge protection when I install a new battery.
This was in a new van (new to me that is) and I think I must have left the radio on when trying to find out what all the wiring by the previous owner did. Needless to say the radio is now disconnected and I'm going to tidy up the accessory wiring.

Regards,
Lester B

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