Very odd trailer light problem...

bevans6 · December 02, 2009, 08:03:17 AM

so I was testing my tow dolly with my bus today, proving in my install of the Gumpy converter. What I did, since I like redundancy, is install a dedicated 24v to 12v converter to power the trailer lights. I wired it so that it would also charge the breakaway electric brake battery on the dolly. What happened is that when I plugged the dolly into the bus, with the bus off, parking brake set, and main switch off, is the engine stop air cylinder Skinner switch puffed air and the brake lights on the bus came on! Wot is hup wit dat, sez I...

When shopping for a 24 volt to 12 volt converter, I bought the simplest and most robust unit I could find. It actually a neat device - it is also a 20 amp equalizer, and as a converter it converts 10 amps of 24 volt DC to 20 amps of 12 volt DC, nominal (it actually exactly splits the input voltage) or it converts 20 amps of 12 volt nominal to 24 volt DC. What happened when I plugged it in to the dolly is the little battery on the dolly supplied 12 volts to the converter, which converted it to 24 volts which fed into the buss that I drew power from, which is connected to the main buss system, which powered up the whole bus... Thankfully, the only things that were on were the skinner valve for the engine off cylinder and the brake lights, since the parking brake was set...

fun, huh? I am proud of myself, it only took me 10 minutes to figure this out!

Cheers, Brian

PP · December 02, 2009, 08:31:19 AM

Only 10 minutes, I'm impressed. When I wired up my toad it took me almost an hour to figure out that the brake lights were on because of the parking brake on the bus, duh

gumpy · December 02, 2009, 09:52:54 AM

Yeah, that's an interesting problem.

That's pretty good. It took me longer to read and understand you description than it took you to figure it out.

At least it wasn't that dang Gumpy converter you bought! Was getting nervous there....

So is this equalizer supposed to work both ways?

You could get a diode and mount it to the output circuit breaker on the toad converter. That would take care of that.

You also need to be a bit careful connecting your brake battery directly to the toad converter. A dead battery could potentially draw more than the 10 amp circuit breaker can handle. You might need a current limiter on the battery charge line.

craig

bevans6 · December 02, 2009, 10:14:57 AM

the converter is actually pretty cool. It's here: http://store.solar-electric.com/12to24or24to.html

It works as a bi-directional converter and as an equalizer. I think it's really an equalizer that happens to work as a converter, I think a Vanner would probably do the same thing. I fused the connection to the battery, it comes directly from the feed from the 12 volt supply, it doesn't go through the Gumpy box. Rather than play with it right now I'm probably going to just wire up a plug to the trailer that lets me connect a charger and charge it up from time to time. I have several trailers and probably should have done that a long time ago!

A diode would also drop the charge voltage to the little battery by .7 volts, if I recall correctly, which would drop the 14 volts (50% of the charging voltage on the start batteries) I get from the converter to 13.3, which would effect a trickle charge to the trailer battery if I have my sums right. What do you think?

Brian

gumpy · December 02, 2009, 10:30:43 AM

don't know what i was thinking. of course it wouldn't backfeed through the toad converter unless your lights were on activating the relays, and why would you hook it through the relays anyway, unless you only wanted to charge when your lights were on! Duh!

I'm not sure of the diode figure, but it sounds reasonable. Easy enough to measure, and if accurate, 13.2 trickle would work just fine for that battery. Might be off a bit, though, as I think your bus regulator should be set to 27.2 (the 1979 manual i'm looking at is saying 27.5), if I recall correctly. Might want to check on that. i think 28 will boil your batteries excessively.

DaveG · December 02, 2009, 05:20:49 PM

FWIW, some of the trailer break-a-way battery kits we sell these days have a little "charger" in the battery box and some of the other newer ones have an LED state of charge indicator lights with push button. What I am getting at is some of these might be configured to allow power in to the battery, but not power out the same wire (charge wire).

Could do some more checking if you'd like, or get you the part numbers, etc.

bevans6 · December 03, 2009, 04:58:05 AM

I would appreciate the detail on that. My other trailer does have a little box inside the battery compartment, but i confess I have ignored it and what it does, because it always just kind of works... If it ain't broke, I try not to fix it! But now I need to make sure everything is going to work, with my truck or my bus doing the towing.

Cheers, Brian

paul102a3 · December 03, 2009, 01:30:53 PM

This is a little off topic but I use the exact same converter to power the control systems of my diesel electric conversion in a boat and after 6 years, 1,200 hours of use, it has never failed or even hiccuped.

I have no affiliation with the company but they make a great product and customer service was terrific.

Paul