Low-Voltage Battery Alarm

[rseagle]

I was snooping around my winterized CCD this afternoon and was putting distilled water in my house battery. I noticed that my Power Pulse Desulfator LED wasn't flashing. I checked the monitor panel and it read 13.6 VDC for the battery. Looked good, I thought. I checked the 30 Amp fuse at the battery. Good. Voltage at battery read 3.0 VDC with a volt meter. Dead as a doorknob! What happened? I started troubleshooting at the ManateK 7300. Breakers were good. 30A fuses were good. 120VAC shore power was converting to 12 VDC OK in the trailer. Lights and stereo came on. But when I unplugged the shore power everything went dead. I sat down to check the 20 Amp fuses on the fuse board, but cut my knee on the cover corner. I'll have to see if a 20 Amp fuse blew later. I didn't want blood to drip all over the trailer. Yeh, it was that bad. A mess. Anyway, I hope it's only a blown fuse. If not, the charger is bad. I did get a 1 year extended warranty from Parrallax, so I'm still covered.

The battery is probably a lost cause, so it'll have to be replaced. My question, finally, is does anyone use a low-voltage battery alarm (similar to smoke detectors) that will chirp or sound when the battery drops below a pre-determined setting, say 11.9 VDC? If I had one, my battery could have been saved. Can anyone recommend a brand?

[lewster]

Hey Bob,

Don't know of any for automotive use, but there are a bunch for motorcycles that would do the job nicely. Look at Kisan Technologies or Kuryakyn.com. You should find a few there.

[rseagle]

Thanks, Lew. I'll look into getting one.

Also, I was thinking that the charger must be OK because I was getting 13.6 VDC to the minitor panel. Something must have happened in the circuit between the monitor panel and the battery. The 30 Amp fuse at the battery was good. I'll give the fuse holder a voltage check and check the connections on the monitor panel tonight. Other than wiring, what else is between there? Maybe the "Battery Store" switch. That suppose to be open when shore power is applied.

[Buttercup]

I don't know how handy you are with electronics but you could build your own low battery alarm from a kit.
I found one for about $7 from qkits.
http://store.qkits.com/moreinfo.cfm/FK915



A kit like this can be assembled in about an hour. The included instructions with kits like this are very simple to understand.

[overlander63]

Originally Posted by rseagle

Maybe the "Battery Store" switch. That suppose to be open when shore power is applied.

IIRC, the "store" position isolates the batteries, if it did that, you would get no charge to the battery, as well as not getting anything out of it.
Turn it to "run", or however the I-want-to-use-the-battery position would be, and try charging the battery you have for a while. You MAY luck out, and it will come back, at least for one more camping season.

[garyk1970]

i hope the battery switch will resole your problem.if you need a new battery i recommend an optima(yellow,blue,red top)my battery goes completely dead (o volts)every winter and this does not damage it unlike a "plate" battery.no possibility of "fumes" inside camper , no corrosion on battery terminals.youre on the right track checking everything with your metter.if not switch, usually a loose/bad connection somewhere.

[DreamStreamr]

Yeah, Bob. Same here. I was going to move the AS to work on it and no tongue jack. Everything inside working fine. Check battery voltage. 3 volts. Well, crap. Battery overcharged and gone. My fault for leaving isolation switch ON and connected with battery to converter.

Now have AGM and will keep battery isolated when storing. Shopping for nice digital vm to monitor battery better, without spending too much for vm. FUN!

[Zeppelinium]

In my vintage trailers I replaced my Univolts with Intellipower(s). As part of the converstion, I installed an 8-place fuze block, the type that uses automotive fuzes. The neat thing about this block is that either or both batteries can be completely disconnected by pulling its fuze. This provides independent protection for each battery in case of a short and a cheap (vice the $20 copper knife switches usually used for manual battery disconnects).

Oops, I hear the squawks out there--how can this small fuze block handle big battery cables? News flash--you aren't starting a cold motor with these batteries. You don't need bazillion Amp wire. Depending on your charger, #8 or #10 wire is more than sufficient to handle the 12 Amp demands of your trailer. It looks funny, but only because you're used to seeing how a battery is installed as starting power in a vehicle.

Generally speaking, you NEVER want to discharge a battery at a current that would take the battery down to 20% charge in less than 2 hours (and you'd stop at 20%, right? to prevent damage). So for most batteries, MAX current should be limited to 50 Amps and the average (not including all that time it is zero) should be WAY LESS.

The one variable you have to worry about is when you've been out boondocking and have discharged the battery to a low level. The initial charging current, lasting tens of seconds to maybe 2 minutes, will be as high as your charger can deliver. But within that time, charging current will decrease to capacity/6, or less than 20 amps for most batteries. A 40 Amp converter solves all these problems automatically!

For those of you with 1000 W inverters, have a good day, ignore the above, and turn down your HD TV when you're in the wilderness... ... it will be dark (and quiet) real soon.

[RoadKingMoe]

If your Airstream wiring is anything like ours, the master cut-off switch does NOT disconnect the converter from the batteries. On ours, the batteries' positive terminals lead to 50A circuit breakers and then to a common bus bar through #6 wire. The converter output attaches to this bar with unfused #6 wire. On the bus are three more circuit breakers, a 50A that leads to the main breaker panel through the master cut-off switch, a 30A that leads to the charge pin on the 7-way tow vehicle plug, and a 20A that leads to the break-away switch.

Look for the first breaker you come to after the battery terminal on the positive cable.

[RoadKingMoe]

addendum to above: just noticed you found and checked a good 30A fuse at the battery. Keep tracing that wire back until you find where the converter connects in. Yours may have a fuse at that point as well.

[rseagle]

Here is an low voltage alarm that might be worth investing in:

http://www.batterycellmate.com/bat_alarm.html

Further trouble shooting of my situation revealed that no voltage or continuity at my battery leads or the fuse holder at the battery. The 30 Amp fuse was good.

Troubleshooting my voltage at the converter/charger fuse block between the blue wire and the DC ground (with all the fuses removed) indicated 13.67 VDC. This is an overvoltage situation according to the manufacture's schematic. Since the battery was disconnected and no substantial appliances were operating, a "short circuit" condition exists. Running an AC outlet check indicated an "Open Ground" condition at my wardrobe/galley outlet and night stand outlet toward the front of the trailer. All others outlets were good.

I take the trailer back in to the dealer service center on Monday. They corrected a "short" to my refrigerator and replaced CB4 last September. I wonder if they caused this situation while fixing the last situation.

[rseagle]

Well I got my trailer back from the shop this week.
Tha VAC problem was a loose crimp in a circuit between the outlets in the galley. An easy fix, but not cheap.

The DC problem was that the Battery Isolation Switch was inadvertantly switched to STORE with the shore power hooked up. Even though I was getting 13.7 VDC to the coach from the converter, none was going to charge the battery. The Red light was on. Yet, all the Phantom Loads were eating away at my battery capacity. Great setup, huh!

Anyway, when the battery voltage drops below 10.5 VDC, switching the Isolation Switch to USE does no good because there's not enough battery capacity to energize the isolation soleniod switch under the front bed. You either have to hook up your tow vehicle with the 7-pin connector, or use a another charger hooked directly to the battery to recharge it above 10.5 VDC.

I'll be more cautious about ensuring the switch is always set to USE while hooked to shore power, but I think I'll still hook up an alarm to warn me if the voltage ever drops again for any reason.

If you're reading this and your trailer is charging on shore power, you might want to check and make sure your battery voltage is above 10.5 VDC and your Battery Isolation Switch is in the USE position.

[DreamStreamr]

Bob
I always kept battery connected to converter when on shore power. I was careless and let my battery run dry. 2.9 volts. This seems too easy to do since the converter doesn't seem to be multi-stage -- it just drives 13.77 volts all the time to the battery whether the battery needs it or not. A good friend always kept his battery disconnected while storing, but reconnected one day every few weeks. His battery survived magnificently. Hmm, how about an autodialer on that low voltage alarm you're creating? No, I just need to pay better attention to what I'm supposed to be doing. BTW, my pictures are posted for our battery replacement with the AGM in case you're interested. I don't know how to place a link to them but everyone else on this forum probably knows way better than I how to find things here. Later. . Jim

[rseagle]

Hi Jim,

I thought our Parallax 7355 was a DC output “electronic switch mode” converter/charger that trickles down as the battery reaches full charge. At least that's what I think it means in the attached. I could have misunderstood it. See what you think.

http://www.parallaxpower.com/

[DreamStreamr]

Bob,
We have some excellent electronics types reading these forums. I think you are probably one too, so I'm not too sure you aren't leading me into something way over my head in this question. I referred this to a good friend who has been working on some issues with his Parallax and is fluent in Electronish.

But isn't the answer that the switched power mode thingy has to do with the AC-DC conversion and not about being an excellent battery charger? My meager understanding is a switched mode power supply has a switching regulator on the load current to keep the output voltage steady. In the case of the battery charger part of the CCD's converter it still lacks, I think, the capability to maintain float charge dynamics for our battery's health.

How about it all you electronics nerd-types? You guys are so great on this stuff -- I just know about life safety codes and stuff and missed out on all this cool (and more useful) tech knowledge. Can you lend a pen onto this question?