Topic: Convert 7747 (daytime) FARS to a 24-hour FARS

[CW7221]

Ok--got a daytime FARS because, as spring started, my daytime temps were about 7ºF above MADIS projections.  Now, as we start to get summer-like temps, my overnight temps are spiking while daytime are within acceptable ranges.

I noticed, while installing the 7747, two spots molded into the fan plate that were clearly intended to be battery compartments--my assumption is (and was at the time I bought the daytime-only model) that the only difference between the two models was the night-time power supply.  

Based on the molds, I'm guessing that just some other hardware is needed to convert the 7747 into a 24-hour model.  Based on the 775x install instructions (7750 FARS Manual), I'm most likely need to get a pair of 1.2v NiCads, wires and "battery covers"--the big question is; does the junction board in the 7747 have terminals for the batteries (without pulling mine apart again)?

Would anyone have any idea if this is do-able, or should I just get a 24-hour model and dump the daytime model?

Thanks in advance!


-Tim

Eichman.net Weather

[dalecoy]

When I last checked with Davis:

1.  There's no kit to add 24-hour fan, at all.  If you didn't buy the VP2 with it, you can't add it.

2.  There's no kit to add 24-hour capability (batteries) to the daytime kit, and although there is a place for the batteries, they won't tell me how or what to add.

3.  Nobody else has revealed info, either.

I'm interested in the same thing you are, so I hope somebody has better info.

[CW7221]

I'm interested in the same thing you are, so I hope somebody has better info.

Figured I wasn't alone... If I find anything out, I'll let you know (maybe I'll pull mine apart again this weekend to take a close look at [and photograph] it to see what might be done...).


-Tim

[bigdog660]

I've done it to a daytime FARS VP1. The only reason I was able to was because I had ordered a 24 hr. FARS VP2 for my house (my Dad has the VP1), and copied the circuit board. Basically I made my own with a printed circuit etching kit from Radio Shack. You will also need a couple of resistors, a diode, 2 NiHM "C" size batteries, and a couple of connectors (looks like PC fan connector).

I do not remember the value of the resistors, but I know the batteries were rated 1500ma/h. All I could find was 1200ma/h; however it has been working over a year now just fine. I bought batteries with tabs for easy soldering and to resolve the missing connectors.

Also lacking are the battery covers and connectors. Although probably not recommended, I just cut a piece of duct tape to cover the battery. I probably could ask Davis to send me the two covers.

Beware if you call Davis and tell them that you want to buy the circuit board, batteries, and you tell them what you are doing (changing a daytime FARS to 24 hr. FARS), they will not help you (they won't even send you the parts). Not that I'm condoning lying here, but probably the part you'd want the most is the battery covers (with seals).

If someone can scan the circuit board (my station's on the root), and post it (front and back), you'll see it's very easy to make.

Hope this helps.

[dalecoy]

I've done it to a daytime FARS VP1. The only reason I was able to was because I had ordered a 24 hr. FARS VP2 for my house (my Dad has the VP1), and copied the circuit board. Basically I made my own with a printed circuit etching kit from Radio Shack. You will also need a couple of resistors, a diode, 2 NiHM "C" size batteries, and a couple of connectors (looks like PC fan connector).

I do not remember the value of the resistors, but I know the batteries were rated 1500ma/h. All I could find was 1200ma/h; however it has been working over a year now just fine. I bought batteries with tabs for easy soldering and to resolve the missing connectors.

Hope this helps.

So, are you saying that the only parts (other than the batteries) are:

2 Resistors
1 Diode

?  If so, it's a very simple charging circuit.  (I would have expected at least two diodes).  Not a big deal to design.  The next time I have a chance, I'll measure a couple of things, and give it a try.

[bigdog660]

Yes, that's about it. There might have been a electrolytic capacitor too, but it's a common value (something like 4.7µF?). I'm going to try to post some pictures tomorrow.

[Jim]

Were you able to figure anything out. I am in the same boat as you.I just got the daytime FARS and if I knew the value of the resistors and the diode I know I could make It work I run A CNC machine in a machine shop and the battery covers would be a piece of cake to make. any help would be appreciated
Jim

[G2003]

Hey, everyone!

I'm VERY interested in doing this, but i'm not very good with electronic boards. Does anyone have a diagram of the board. Or better yet, if some would could make me a board, i'd be glad to buy one!

[xmas111]

Also lacking are the battery covers and connectors. Although probably not recommended, I just cut a piece of duct tape to cover the battery. I probably could ask Davis to send me the two covers.

I have the VP1 with the 24 hour FARS and as for the batteries it's a pain in the neck to replace them. You have to remove the FARS and that's not fun.

What I did was run the wires from the VP1 battery compartments to a external closure. Then I bought a battery holder from Radio Shack and placed the batteries in the enclosure.

I haven't had to replace the batteries yet but it will be a snap when needed.

Here's a picture of the enclosure, it's the small gray one beneath the VP1 enclosure.

Hope this helps to simplify the modification.