Heater inside repeater case?

Birken Vogt · Post by **Birken Vogt** » Fri Dec 02, 2005 6:47 pm

I am about to install a TKR-720 in a remote site where it probably will get down to 0° in the winter and looking for a good solution to keeping the radio stable. Since the power does go out up there, it will have to be able to run on batteries so we were toying with the idea of an internal 12v heater. Is this idea crazy, and is there such a thing we could buy ready made?

Birken

Alan · Post by **Alan** » Sat Dec 03, 2005 10:47 am

Unless you have a few weeks of back up battery power, I would skip the 12 volt heater. It will just reduce your battery run time.
I have bought small 110 volt heaters from the electical supply house. It looked like a large heatsink. I think they were available in 100 or 200 watt models.
I can dig up a brand/model if required.

440roadrunner · Post by **440roadrunner** » Sat Dec 03, 2005 11:38 am

I have no idea what your delta from high to low temps is, but I think depending on heaters is ill advised.

Remember, a heater that's only 100 watts, on nominal 12-14V, wil draw a pretty substantial 7-8 amps.

How about this? I assume the radio is in an enclosed cabinet? The gear itself will generate some heat, how about installing thermostatic fans to operate when the cabinet temp becomes warm, and configuring the cabinet (insulation, vents, etc) to take advantage of the radio's inherent generated heat?

I assume normal operation entails 120V AC being available? Can you just apply 120V heaters, and "wing it" during outages?

RKG · Post by **RKG** » Sat Dec 03, 2005 12:05 pm

According to the TKR-720 Service Manual (B51-8088-10(N)750 (1994), the unit is rated for operation in the temperature range -22F to 140F. Note also that the frequency standard is TXCO, which implies that, within this range, cold should not cause the station to operate out of spec. (Frankly, I'd be skeptical about operating it at 140F and expecting within-spec stability and power.)

We have two TKRs that sit in an unheated building through the New England winter (peaks at about 0 or so for a low) and summer (peaks at about 100 or so for a high inside the building). Both have been operating for over 10 years with no apparent failures of any kind.

Birken Vogt · Post by **Birken Vogt** » Sat Dec 03, 2005 12:06 pm

This is a high mountain site that never gets very hot in ambient temperature so the battle will be keeping the place warm. A 120v heater is the obvious solution but without it, it will get cold, and very fast. We are thinking probably 0 degrees is a reasonable minimum. At that temperature we are thinking at best the radio will be quite a ways off frequency and at worst may not even work at all. And of course when the power goes out is when it is needed the most. Rather than being on a dead end line like most repeaters, it is actually in the middle of the line that feeds the town that it serves. There is no power grid here, a single line is all that feeds the town and it goes through miles and miles of the steepest, snowiest, most heavily forested areas ever seen, on poles, hardware, and wire that have been there since the 30s. That is what is left, a lot of it having been smashed by falling trees as evidenced by broken stuff laying all over the ground under the lines.

So anyway, my thought is that to have a radio that will last a while on batteries is better than to have one that will have plenty of juice but is frozen up by the cold. I dunno, maybe it would be better to have it slowly drift toward uselessness instead...in any case you can bet that anything bad that can happen to this site, will probably happen at some point.

Birken

Alan · Post by **Alan** » Sat Dec 03, 2005 3:19 pm

Look at the temperature spec on the repeater. There will be no issue at all with it operation down to 0.
The unit will be frequency stable well below that.
The main reason for the heater is to drive out moisture for long term reliability, not for short term operation.
Look at the picture in this link http://www.danelec.com/library/english/newsletters.asp

Do you think that they have any heaters at all in there? This is a British Columbia Forestry (or Highways) site. They run mountain top stuff all over the province without the aid of heaters.

But, just for aruguments sake, lets say you do put in a 12-volt heater. Lets say a 200 watt heater. That means about 16 of 17 amps of current at 12 volts to run that heater (if it's that cold it will run steady). How big of a battery bank will you have to give you a couple of days back up. You will need at least 800 amp hours of battery capacity just for the heater, not even allowing for the repeater load.

psapengineer · Post by **psapengineer** » Sat Dec 03, 2005 6:15 pm

This is kind of a brain teaser question.

Batteries, when cold, do not deliver much energy. How are you going to keep the batteries warm?

How long is the typical longer utility outage?

Will the batteries have a LVDC (Low Voltage Disconnect)?

How long will the batter plant last in normal tempratures and typical duty cycle?

Can you get to the mountain top late fall and late spring?

Will the batteries be sealed or vented?

Is this a ham, commercial, or public safety application?

Let us know............ Bob

psapengineer · Post by **psapengineer** » Sat Dec 03, 2005 6:22 pm

I posted a few questions but here's where this is leading:

I'm envisioning a system that, when cold, keys the repeater for a few seconds each 10 minute period and sends a CWID. Double insulate the box really well and the quiescent dissipation and intermittent keying could keep it warm and eliminate the need for a heater.

Bob

RFdude · Post by **RFdude** » Sat Dec 03, 2005 6:47 pm

Capex versus Opex, that is the question. Pay capital money now to buy a system like the Daniels that will go down into deep freeze and still work, and enjoy low opex costs later. Or choose the cheap radio with some sort of heater, or other consideration to keep it warm, and you may have reliability and opex costs to contend with on an ongoing basis.

I've even bought used Glenayre mountain top radios from BC and they are still in serivce now after many years on my hill top with virually no maintenance... and solar power only. -40 to +40C in the shelter. NO worries.

The other thing you can try is to put your proposed radio into a freezer. Get it down to -20C or so then pull it out and see how it works. As quickly as you can before it warms up, check the freq stability (Both tx and LO), and note the receive sensitivity. You may have to tweak the frequency reference. I pick a middle of the range temperature, like FREEZING (0C/32F) and make all my adjustments at this temperature.

RF Dude

Birken Vogt · Post by **Birken Vogt** » Sat Dec 03, 2005 8:50 pm

I see your point. I was thinking more of a heater just for the channel elements, whatever they may be (have not looked at the radio in a long time.) It is already in service but we are just moving it to a new location. I do agree that the freezer is an excellent notion. Now I need to figure out how I can go about actually doing that experiment. The radio is one of many selectable by tones on a countywide fire department system but its purpose is basically to serve one small VFD who has trouble with coverage. There are two other, more reliable repeaters they can use in a pinch but the coverage is much worse. The radio can go for days without transmitting so much as a peep so nothing to help keep it warm really.

Birken

nmfire10 · Post by **nmfire10** » Sun Dec 04, 2005 12:45 am

Again, the TKR can handle 0 degrees just fine with no heaters. -22 way below zero. You don't need heaters to keep the radio working properly. It will be just fine on it's own in the cold.

Instead of wasting you money heating something that doesn't need to be heated, spend it on a battery system that won't be a usless brick at 0 degrees.

Birken Vogt · Post by **Birken Vogt** » Sun Dec 04, 2005 7:04 am

Yeah I guess I should have looked at the spec sheet before posting this question. Since then I have looked at the specs for all the other components except the power supply (can't remember what it is) and they all say the same thing, -22.

So, I will simply install a 120v heater to keep the moisture off.

Any words of experience on how much battery this should take? The system is the TKR-720, and a ~110W TPL amp. Estimate 2 hours of transmit time per week. Right now it's got a pair of group 31s I think.

Birken

nmfire10 · Post by **nmfire10** » Sun Dec 04, 2005 7:41 am

What do you have for a power supply and what do you have charging the batteries right now?

The float charging I've found by nature will make a little bit of it's own warmth for the battery just because there are electrons flowing. Putting a battery blanket around the battery to help keep that heat in might be helpful. Deep cycle marine, and even better, gel cell type batteries are sealed and much better than lead acid batteries.

My knowlege of batteries is pretty much limited to that. I'm sure there is someone here that knows of something quite perfect for this.

jim · Post by **jim** » Sun Dec 04, 2005 11:18 pm

Optima batteries work well and last for years. Some will argue that you need $500 "site" batteries, but so far I haven't been able to see a performance difference between the yellow Optima and a "site" battery and for 1/4 the cost......

For heat, a simple 130VAC 60W light bulb will do wonders. Use a "DC puck" in the base of the socket since DC will allow the filament to last longer.

RKG · Post by **RKG** » Mon Dec 05, 2005 7:07 am

A quick and dirty on battery backup.

First, figure out your average draw (xmit power * xmit duty cycle + rx power * rx duty cycle + standby power * standby duty cycle). The result will be watts. Divide by 10 to get amps. Now decide how long you want the radio to be able to run on batteries (in hours) and multiply that by the result of the first calc; the result is AH. Double that figure and that is the size of the battery bank you want.

I'd stay away from Optima batteries (grossly overpriced and only mediocre performance) and flooded cells (require maintenance and severely degraded by cold) and go for a premium deep cycle gel cell. My recommendation is Group 31 8G31DT by East Penn. These are worth about 95AH per battery; additional capacity comes by wiring multiple batteries in parallel.

Now, acquire a TruCharge smart charger. Comes in 20A and 40A flavors; I'd go for the 40A assuming you'll need between 2 and 4 of the gel cells wired in parallel. Wire the charger to the battery bank, program it for gel cells, and plug it in. Whenever there is utility power, the TruCharge will fully recharge your batteries (as fast as is possible) and then float them while simultaneously serving as a battery eliminator to power the radio.

Foregoing assumes the radio can be configured to run of 12VDC, and is connected directly to the battery bank. No switching is needed; when utility power is lost, the TruCharge stops and the batteries continue to power the radio. When utility power comes back on, the TruCharge will automatically restart itself in bulk stage.

If your radio has to see 110VAC, then you need to wire an inverter to the battery bank and the radio to the inverter. In this case, I'd substitute a Heart Interface Freedom 10 for the TruCharge: it combines a smart charger (50A), an inverter (1KW) and a very fast transfer switch (about 20 msec). When there is utility power, the Heart will simultaneously charge and float the batteries and pass utility power to the radio; when utility power is lost, the Heart will switch to inverter mode and power the inverter, which will power the radio.

The gel cells neither need nor tolerate any maintenance; once every year or so I'd load test them. So long as they are not drawn below the 50% point, they should be good for 500-750 deep cycles, though in your application, life is a function of time alone and not cycles, and they should be good for 5-10 years.

Since the site is not manned, consider wiring in a low-voltage cutout switch. Depending on the device used, this can be programmed to cut the batteries at something like 11.2 VDC or X AH (50% of nominal capacity), which will cause the radio to shut down but prevent killing the batteries altogether.

Very approximate cost:

8G31DT's: about $150 per battery.
TruCharge 40A: about $300.
Freedom 10: about $800.
LowV Cutout: about $200.

nmfire10 · Post by **nmfire10** » Mon Dec 05, 2005 7:22 am

RKG- Optima's are[/i] gell cells. Are you sure you're not thinking of something else? All those things you listed as being good about gells cells are benefits of an optima.

We have a charger / power supply on our TKR-850 that does the same as that TruCharge. It provides 13.8vdc to the radio and charges the batteries when there is AC Power. When AC fails, it switches over and sends battery power to the radio. I even has a little display on the front that will tell you volts & amps. There are also status and alarm contacts on the back for site monitoring. I forger who makes it, I will look when I get home.

The 60w lightbulb is so simple, it's one of things that makes you go "DUH!" when you hear it. You can get a 4-pack of 'heaters' from the supermarket for $1.50 and you'll have a source of light when you're working on equipment!

Oh yea, whatever you do... never let it end up like this!
http://batboard.batlabs.com/viewtopic.php?t=29071

Birken Vogt · Post by **Birken Vogt** » Mon Dec 05, 2005 7:36 am

This I do know (I am a mechanic and electrician by trade not a radio tech): Optimas are AGM which is Absorbed Glass Mat. That means that they have a fiberglass-like substance between the plates that is filled 90% to capacity with acid. This means there is air space all throughout the electrolyte so if they do get frozen they do not expand and crack the case. Gel on the other hand has a silica in its electrolyte which makes it like sloppy Jello. Not sure how they react when frozen. I had been leaning toward Optimas because that way if the power does go out I can let it run until it won't work no mo' and just let them freeze at that point. Not the best for the battery but the best for the firemen anyway....

Probably what I will most likely do at this point is leave the existing flooded batterys in their tubs and if they break they break, at least they are contained, and if I come back in spring and they are broken, then decide what to do, otherwise I will leave them in there until their life span is up, we did just buy them IIRC (this is after all moving an existing repeater installation).

The power supply is also fairly new I think, or has just been repaired, it is a model that is designed to supply the radio and charge a battery and switch over automatically.

As far as the heater, I am not to keen on light bulbs, they burn out at the most inopportune time and one fine feature of the Sierras is it can get quite warm when the roads are still impassible by snow (and mud) so I would not want to toast it in spring before I can get up and turn off the light, neither would I want it to burn out in the dead of winter where there is no hope of accessing the site, nor would anyone know anyway. The light might also attract shotgun toting vandals and punks....

I know some fire sprinkler closets I have seen have small thermostatic electric heaters built in but I am thinking I might even be able to find something at Kmart that will work.

Birken

Nickb · Post by **Nickb** » Mon Dec 05, 2005 8:54 am

I second RKG's battery recommendations. East Penn makes both AGM (adsorbed Glass Matt) and Gel battery types, so you can take your preference. I would avoid batteries designed for automotive use.

For heaters, how about an automotive 'battery blanket' that wraps around the battery? Keeps batteries warm while heating the cabinet. When AC goes, batteries will cool off very slowly and you get best power from them. Will probably still be warm by the time they get fully discharged.

You should be able to find some kind of off the shelf thermostat for them too. Maybe a baseboard heater thermostat, turned down to its lowest setting? Or another automotive idea, a thermostat for a block heater ?

440roadrunner · Post by **440roadrunner** » Mon Dec 05, 2005 10:47 am

Probably a better idea than a "light bulb heater" is a "light bulb heater."

Instead of using a 120-130V lamp, use a 240V lamp, but OPERATE it on 120. The bulb will last forever. You of course will have to use a bulb rated at 4 times the wattage to get anywhere near that out of a 240V bulb. In my Mom's old wellhouse, in the winter I use a 200W 240V bulb--so about 50watts at 120.

RKG · Post by **RKG** » Mon Dec 05, 2005 1:12 pm

Those who are interested (really interested) can find a lot of literature comparing battery chemistry. Particularly in the last few years, there have been a number of papers done on AGM batteries. Most have concluded that the AGMs, which are sort of a cross between valve regulated gel cells and flooded cells, where the liquid electrolyte is absorbed in the glass strands rather than just sloshing around, provide no benefits over well-made gel cells.

Optima batteries are a subspecies of AGM. They do have one standout trait, and that is vibration resistance. As a result, the Optima starting batteries are widely used in racing and off-road vehicles -- for starting purposes. The starting Optimas are not deep cycle batteries.

No battery should be 100% discharged. A flooded cell that reaches OCTR (open circuit terminal voltage) of 10.5 VDC -- which is the definition of completely discharged for a nominal 12 volt battery -- is dead. It cannot be recovered. Well-made gel cells can take one or two complete discharges and be substantially (though not fully recovered), but their cycle life will be impaired. AGMs are, in this respect, closer to flooded than gels.

One primary advantage of gels over flooded is that they can be recharged (by a properly programmed multi-stage charger) far more quickly than flooded cells. And, because they can be bulk charged below the gassing point, they do not gas and do not lose electrolyte. In this respect, AGMs closely mimick gels.

A flooded cell that freezes will crack its case and become useless (at best; dangerous, at worst). What happens is that the chemicals (primarily sulphuric acid) dissolved in the water component of the electrolyte precipitate out and the pure water freezes. It is all but impossible to freeze a gel cell; an AGM can freeze.

nmfire10 · Post by **nmfire10** » Mon Dec 05, 2005 1:20 pm

Crap, you're right. Not sure why I had gell cell in my head for optimas.

jim · Post by **jim** » Tue Dec 06, 2005 7:19 am

Either way, a battery shouldn't sit in a site for more than 5 years. A yellow Optima OR you choice of a $600.00 site battery will both work. I still don't like a 50A charger on any floating cycle battery. There's no need to hit a battery tha hard. A simple 10A smart charger will charge an entire bank slowly and not overheat them.
Optimas actually weren't deisgned for automotive use either!

RKG · Post by **RKG** » Tue Dec 06, 2005 2:17 pm

1. A 50A charger does not put out 50A in float mode. By definition, it will not enter float mode until the charger had detected that the batteries are 95% charged (i.e., that acceptance at a nominal 14.5 (flooded) or 14.2 (gel) (in both cases adjusted for battery temperature) steadies at less than 2% (or 2A per 100 AH of programmed battery capacity). Upon entry into float mode, the charger maintains output terminal voltage at about 13.5 VDC (flooded) or 13.8 VDC (gel) (adjusted for temperature), and it will output as much, or as little, current as is necessary to maintain that voltage. In practice, output current upon entry into float mode will be in the range of 1-2A for a 400 AH bank (plus any external load) and quickly tapers to less than 100-200 mA for that same bank.

2. Actually, deep cycle batteries (at least of the lead acid variety, which includes flooded, gel and AGM) do not like to be charged slowly. The like to be charged at a constant current of between 20 and 50% of nominal capacity until terminal voltage reaches a point just above gassing (flooded) or just below gassing (gel and AGM), at which point they should be charged at that setpoint until acceptance reaches the 2% point. Charging this way reduces charging time to a minimum (and therefore reduces sulphation), and it also insures a depth of PbSo conversion in the deeper reaches of the plates that cannot be achieved at lower charge rates.

3. I'm sitting six feet away from a Quantar that is on a power supply much like the one I described. The batteries are two 8G31DTs by East Penn; they are four years old and at last load test (about 6 months ago), they tested at no measurable decrement from nominal. In this application, there is a back up generator, but it is a manual start, so the power supply has to carry the Quantar for as much as a couple of hours before either utility power is restored or the generator is started. In fact, the batteries have spent more than 99% of their time on float, with no impact.

Zaputil · Post by **Zaputil** » Tue Dec 06, 2005 5:55 pm

Look here: http://www.hoffmanonline.com/pdf/Spec-00051.pdf

I used these Hoffman cabinet heaters in the past- they work well for outdoor cabinet. The thermostat is important for those unseasonably warm days.

To agree with some previous points, don't worry about a battery powered heater. Insulate as best as possible. The equipment can take the cold much better than we can!

Good Luck!
SZ

Birken Vogt · Post by **Birken Vogt** » Tue Dec 06, 2005 6:18 pm

I got a "Pick A Watt" heater from the electrical supply place with a thermostat and installed it today. I set it for 250W and the stat is around 60 degrees. The one I got is designed to install in between the studs of a house (zero clearance to combustibles sides and back) which is good because I need all the room I can get. So I did install it between studs.

Now it is a waiting game, waiting for the power company to get the power to the place.

Birken

Heater inside repeater case?

Heater inside repeater case?

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