Temperature compensation for battery

[kell]

If somebody were to manufacture a compact voltage regulator that would install next to or on top of the battery (in the oil tank) that would adjust charging voltage according to battery temperature, how well would it sell; how many of you would buy one? Say it cost 50 bucks.

[dj]

Sounds pretty trick there kell. $50.00 sounds reasonable for an item like this. I'm ignorant as far as the electrical significance of it. To guess, I would think that the voltage would decrease when the batt is hotter? It seems like I remember a thread where you were talking about it. I'll do a search.

[kell]

You remembered right.
Temperature of a battery in a bike's oil tank goes to such extremes that one charging voltage won't work under all conditions, because the best charging voltage at the extreme ends of the temperature range may differ by a couple of volts. At 130 degrees Faehrenheit, charging voltage should be reduced about a volt, compared to room temperature. Around freezing, you should charge the battery at nearly a volt higher than at room temperature.

[panster]

I'd buy a 12V one now.
J.

[Cotten]

Cycle Electric has been making "low" voltage regulators for oiltank applications for many years now.
(I requested the first 12v DC model nearly a decade ago, and I believe it is still in service to this day. After that, CE offered them at large.)

...Cotten
PS: $50 for a hidden unit would certainly be a bargain!

[kell]

I ordered enough parts to build two or three prototypes. I'll let you know when I get them done. They will have aluminum cases 1 inch by 1 inch by 3 or 4 inches. This voltage regulator needs to be in physical contact with the battery. It will use a negative temperature coefficient of about .025 volts per degree centigrade. This is about the average temperature coefficient recommended for charging various batter types, which ranges from
-.018 for AGM to
-.033 volts per deg C for flooded batteries.

I guess I should reiterate, this regulator doesn't have a fixed voltage. The voltage output adjusts up and down with temperature. That's why it needs to be in physical contact with the battery. It will give you the correct voltage when the battery is hot, but it will also give you the correct voltage when the battery is cold -- they are not the same.

[Cotten]

Kell!

Will it be specific for a particular battery, or anything that fits?
Will it need airflow?
(Meaning: will it have a visible heatsink?)
If you can make it look like the original cover, you can probably count on a healthy market!

...Cotten

[59Panman]

Kell,

Are we talking just 12V version or will you also build a 6V model if your prototype works well?
ozwick

[kell]

Cotten, the circuit I'm using in this regulator doesn't produce much heat of its own and doesn't require a heatsink or airflow. The idea behind this voltage regulator is to put it right next to the battery in the oil tank, or maybe on top of the battery. If somebody wants to install it somewhere else they can, but there's a caveat (see below).
I made one yesterday using hollow one inch square aluminum tubing (1/16" walls) and everything fit inside. It has four wires coming out of it: armature, field, battery, and ground. This prototype is almost four inches long but could be shorter. Maybe that would fit into a hollowed out original voltage regulator body, or something, I don't know. But if the installation is on some other part of the bike (not in contact with the battery), that defeats the temperature compensation. If a voltage regulator with temperature compensation is sitting out there in the freezing wind, it will put out quite a bit higher voltage than you want for a battery sitting in a hot oil tank. You would want a fixed-output reduced voltage regulator in that case. The installation is going to determine the type of regulator you should get. If the market wants looks more than optimal function, I can drop the idea of temperature compensation and build regulators with fixed output for installing in other locations on the bike.
Making six volt units is no harder than making twelve-volters, no biggie there. But at this point I'm building by hand and it takes forever. Production in any quantity will require, just for starters, coming up with a printed circuit board design, getting cad software from a pcb fab house, and sending in the design for them to make the pcb's. But for now I'll just build one or two more prototypes for people to try out and see what the market may have an appetite for. Maybe it will turn out the the whole temperature compensation thing has no appeal and it will be a better idea to cater the the desire for something that looks like original equipment, like a miniature regulator that can be installed within a hollowed-out original enclosure, or such.

[Cotten]

Kell!

Units with authentic appearance are already on the market: (http://www.45partsdepot.com/" onclick="window.open(this.href);return false;, click on catagory "Relay")
but temperature compensation isn't addressed.
Please consider an application directly under the battery cover. It sounds like a great idea with real advantages if you can work out the details.

...Cotten

[kell]

Okay, asking for a favor:
Is there somebody here with a stock bike that can mock up a block of wood or cardboard 1" X 1" X 3.5" and see if there's space to hide it under the battery cover, or maybe in some concealed spot behind the battery next to the frame of the bike. Use your imagination. I need to know how small I have to go with these doohickeys to get them where they can be hidden in some crack or cranny on a stock bike from the generator years.

[Cotten]

Can you get it down to 5/8" in one dimension?
Then under the lid is an option.

[kell]

I'll mount the parts on a thin aluminum plate, fold the edges up 5/8" and fill with silicone potting compound. That'll be my project next weekend.

Post by kell

They can be made 5/8" in the least dimension. What are the limits on the greater dimensions?

[Cotten]

Kell!

You really must have a cover in hand to judge your fit.
It will become indispensible when you consider a mount or retainer. Most likely a heavy foam cushion with a snug cavity for your unit will be the easiest, goobered upon the cover so that your regulator is removeable.

....Cotten

[hplhd]

kell, i don't know if this is a bad spot to hide it but i have the small 12v bat sitting on the extension and there is a bit more room under the bat and tray and out of site.