Diversion Heater - Relay Setting

Gbridgem

I have added a HL 100 diversion heater to my set up with a mechanical relay. I am controlling it through my F
lexMax 60 charge controller. I don't think I have the diversion relay settings correct. The relay seems to be cycling on and off and never warming up. It seems like a self fulfilling profacy - whenever the voltage rises to trip the relay, the resister reduces the voltage and trips it off. Yesterday, I was in absorb for the 1hr before moving to float for almost five hrs, with little diversion load production. I would have thought this would have been a good day for the diversion heater.

Any experience / advice with this set up?

Guy

waynefromnscanada

Re: Diversion Heater - Relay Setting

http://www.infinigi.com/hl100-air-heater-diversion-load-p-1656.html

Hate to have to tell you, but it's very likely working as designed. Electric heat takes a ton of electricity.
Some questions for you:
What do you have for a charging supply, solar or small wind turbine? What wattage the panels? Or what make and model the turbine?
What for batteries, what for loads?
With this info, we can be more specific with our answers.
Oh, and welcome to the form

Gbridgem

Re: Diversion Heater - Relay Setting

Have posted a couple of questions before - with helpful replies.

Have a 3x220w + 2x245w PVC panels. Have 8x135ah AGS batteries @ 24vdc. MS4024 PAE inverter. This is a w/e cabin - main load is small electric fridge - but have been leaving inverter off during week when were away - so no load on when we are looking for diversion heat to save on propane. Based on log, seems to hold at 25+ vac all wk.

(BTW - much improved since we added the 2x245 panels this summer, pointed all (roof mount) panels due S and cut down a few trees. Haven't run generator in months.).

Photowhit

Re: Diversion Heater - Relay Setting

So what size heater are you trying to run?

With 1150 Watts of array, you can get a through perhaps 800 DC watts or 600watts AC if things are pretty close to perfect, if things aren't perfect or your using a larger heater, the load will be drawing on the battery and reducing the voltage and your charge controller will shut things down.

Gbridgem

Re: Diversion Heater - Relay Setting

The heater is an "alternative energy engineering" HL-100 "air heating diversion load. We left it at the factory setting of 4 ohm. It can be set at 1' 0.5 and 0.25 ohms.

The highest output I have noticed from the 5 panels since putting them into service in October was 860 w.

I gather that I should be able to divert energy to the heater so long as the batteries are full (voltage above float voltage of 27.2vdc.) and the draw from the heater in watts is less than the panel output (watts).

Question. The charge controller seems to keep it at 28.8 vac in absorb and then 27.2 in Float. When would it be allowed to climb above these settings to ever trip diversion relay?


Guy

BB.

Re: Diversion Heater - Relay Setting

If I understand your question correctly--The voltage should never rise above those levels.

Normally, what is done is the MPPT charge controller (Outback, Midnite, possibly others) have a programmable output that when the charge controller enters "float"--The controller turns on the "float" signal and as long as your loads are less than the available solar power, the charge controller should keep the battery voltage at float.

Once the load current exceeds the solar array output (sun going down, clouds, etc.), the voltage will fall to below ~12.7/25.4/50.8 volts (probably programmable value for many controllers) and the controller will go from float back to bulk/absorb (and turning off the "float" signal).

If you have a separate diversion controller--It will be difficult to coordinate when to turn on the dump load.

One way around it is to set the Absorb voltage "high" (say 14.8/29.6/etc. volts), and then program the diversion controller to be your "master charge controller" and do all of the charging stage/voltage set points. The MPPT charge controller just stays in "maximum" output from solar array all day long.

Diversion controllers are not "as good" at charging a lead acid battery bank--But it does work.

-Bill

Vic

Re: Diversion Heater - Relay Setting

Gridgem,


This question comes up from thim-to-time.

You may need to select the value of hystersis carefully to reduce any chatter.

DC switching can damage mechanical relay contacts. Often Solid State Relays do a much better job of switching.

See this thread on the Outback Forum, and see the link early in that discussion as well:

http://www.outbackpower.com/forum/viewtopic.php?f=29&t=2865

Good Luck, Vic

Gbridgem

Re: Diversion Heater - Relay Setting

Thank's for the link Vic. I revised my settings as follows: relative volts to 0.2 above float and Hystersis to 0.2 meaning (as I understand it) ie should trip to inactive when it falls 0.2 below the relative volts - or back to the float voltage. I also reduced the delay to zero and the hold to 25 seconds.

When we arrived last night around 4 pm - sunset, the relay was active and the thermometer sitting on the heater was 25c - whew was the rest of the basement was 10c. So it must have been on for a decent amount of time. Will monitor it this w/e if we get sun.

Guy

waynefromnscanada

Re: Diversion Heater - Relay Setting

Vic wrote: »

You may need to select the value of hystersis carefully to reduce any chatter.

DC switching can damage mechanical relay contacts. Often Solid State Relays do a much better job of switching.

Vic

So true. Mechanical relays tend not to last long in such use. Too bad you couldn't come across a decent solid state relay, or use hi-current FETs to handle the switching.

vtmaps

Re: Diversion Heater - Relay Setting

BB. wrote: »

then program the diversion controller to be your "master charge controller"
<snip>
Diversion controllers are not "as good" at charging a lead acid battery bank--But it does work.

I have read this several times on this forum, but it is not obvious to me why the diversion controller is not as good. Care to explain? --vtMaps

BB.

Re: Diversion Heater - Relay Setting

Diversion controllers tend to be On/Off type devices... And they are usually sized, at least as large, as the maximum "uncontrolled" charging source...

So, your controller is usually alternating between giving the battery a goodly charge at 14.xx volts and hitting the battery with a 5%-13%-25% load and discharging the battery to 13.xx or below 12.xx volts, then starting the whole cycle over again. Just more overall stress on the battery and the lack of ability of a diversion controller to hold a fixed voltage for a multi hour period.

From our host's Battery FAQ:

Note that many shunt-type charge controllers sold for solar systems will NOT give you a full charge - check the specifications first. To get a full charge, you must continue to apply a current after the battery voltage reaches the cutoff point of most of these type of controllers. This is why we recommend the charge controls and battery chargers listed in the sections above. Not all shunt type controllers are 100% on or off, but most are.

-Bill

vtmaps

Re: Diversion Heater - Relay Setting

BB. wrote: »

Diversion controllers tend to be On/Off type devices
<snip>
So, your controller is usually alternating between giving the battery a goodly charge at 14.xx volts and hitting the battery with a 5%-13%-25% load and discharging the battery to 13.xx or below 12.xx volts, then starting the whole cycle over again.

What is the frequency of this on-off cycle? And don't all charge controllers turn on-off (at least after absorb is reached) to maintain battery voltage?
--vtMaps

Cariboocoot

Re: Diversion Heater - Relay Setting

vtmaps wrote: »

What is the frequency of this on-off cycle? And don't all charge controllers turn on-off (at least after absorb is reached) to maintain battery voltage?
--vtMaps

Charge controllers pulse at a very high frequency to maintain Voltage level. This is very rapid and the Voltage doesn't change much up or down because there isn't much current draw from a fully charged battery. Add a significant load and the controller can be pulled back into Bulk stage.

In this case powering a 'dump' or 'diversion' load to utilize 'extra' solar power you have an instance of engaging a significant load for a much longer time; the Voltage can drop off greatly. If the power available from the solar isn't sufficient to make up for the load, the Voltage sags below the set point for the load and the controller shuts it off again allowing the Voltage to quickly rise back up to where the controller turns the load on again and ...

Lather, rinse, repeat.

Sometimes it's a bit difficult to predict in advance just how much "extra" solar power you'll have available, especially as it tends to vary from one day to another.

vtmaps

Re: Diversion Heater - Relay Setting

Cariboocoot wrote: »

Charge controllers pulse at a very high frequency to maintain Voltage level.
<snip>
In this case powering a 'dump' or 'diversion' load to utilize 'extra' solar power you have an instance of engaging a significant load for a much longer time; the Voltage can drop off greatly.

So you are saying that the problem with diversion controllers is that their frequency is too slow and that the voltage swings are therefore too great? I thought that some charge controllers can be used as diversion controllers, and I thought that their frequency and voltage control were similar in either mode. --vtMaps

Cariboocoot

Re: Diversion Heater - Relay Setting

vtmaps wrote: »

So you are saying that the problem with diversion controllers is that their frequency is too slow and that the voltage swings are therefore too great? I thought that some charge controllers can be used as diversion controllers, and I thought that their frequency and voltage control were similar in either mode. --vtMaps

They can be.
It's all about balance again: getting the right amount of diversion load for the power available.
Since a certain amount of the solar power is needed to maintain Float Voltage of the batteries against the varying 'normal' loads, getting the right amount of 'extra' load to make use of the remaining power available can be tricky. Usually you end up sacrificing some of that power for functional stability.

Ordinarily you'd have something like:
1000 Watts available from array at peak sun minus
100 +/- Watts to maintain battery Float with standard loads leaving
900 Watts available for additional load such as water heating.

Now, put a 1500 Watt element in to heat the water and guess what happens? Every time the dump load is engaged it pulls the Voltage of the system down to where Float can't be maintained and the diversion load is switched off causing the Voltage to rise again.

Change the load to <900 Watts and it remains stable for hours until there isn't enough sun to maintain output from the array or some other load comes on demanding more power.


I believe MidNite has a very nice diversion control system in their Classics which can attend to the disparity, tailoring diverted power to whatever 'extra' is actually available.

BB.

Re: Diversion Heater - Relay Setting

The charger has to pretty much "micro discharge" the battery by the amount of excess charging energy to refill the battery back to turn on the dump load again.

Could a shunt controller run at high enough frequency (100's to 10,000's of Hz) to make use of the "capacitance" of the battery to store the excess charging energy between "cycles"--Perhaps (they may even do that now--I don't know).

But you are talking about switching ~60 amps to a load vs switching ~6 amps from the series type controller. Lots more noise in the system.

There are other (older/smaller?) shunt controller designs where the shunt (load or dead short) is applied to the source and a series diode blocks the battery bank from back-feeding into the shunt load. That would prevent the micro discharges (interestingly, the few places I have seen this design were applied to solar panels--which do not need a shunt controller). I have not seen any wind turbine system documented with this particular topology.

Battery Chemistry wise--It is probably an interesting question that not many people have asked/answered.

-Bill

PS: Per Marc's (Cariboocoot) post, Midnite with its clipper system is probably pretty close to the ideal shunt controller inplementation to this date--I don't know if they isolate the battery from the shunt load or not.

Gbridgem

Re: Diversion Heater - Relay Setting

I watched the diversion relay yesterday with good sun and my actual on / off experience fits well with the posts below. With good sun around noon, (500W) the diversion relay came on part way through absorb and stayed on into float (after 60 min absorb cutoff). It remained on until production dropped below 300 W, (likely a bit more than the 4ohm heater). It then began to cycle, with the heater dropping the voltage, running for the 25 second hold time, then back on when the voltage popped back up to 27.2 plus the 0.2 relative volts. This continued for about 10 min until production dropped below 200W and voltage remained below 27.2 +0.2.

To reduce chatter, I increased delay time to 5 seconds (to avoid momentary recovery above 27.2 + 0.2.). Looks like cycling is a transition phenoomenon when there is not quite enough surplus production to drive heater without dropping voltage below hyst cutoff.

Looks like a process of trial and error with the settings. i have both relative and hyst at 0.2. Maybe increase them both to 0.3. May not come on as much but reduce cycling. If the cycling kills the mechanical relay, could look at replacing it with more expensive SS relay and just live with the inevitable cycling when this combination of production, load and battery state of charge materialize.

In the meantime, any further advice / experience with mechanical diversion relay settings would be appreciated!

Guy

Gbridgem

Re: Diversion Heater - Relay Setting

It has occurred to me that the mechanical relay I installed to control the diversion heater is a bit of a clumsey device for this purpose. As this is simply on and off, I will always get the cycling when I am on the edge of having enough power to operate it. Adjusting the settings may reduce cycling at the cost of some production.

Am I correct in thinking that I would not get on / off cycling had I installed a solid state relay? The relay would prorate the power between the batteries and the relay to hold their charge at the float coltage. A smoother diversion control process?

Guy

stephendv

Re: Diversion Heater - Relay Setting

BB. wrote: »

Diversion controllers tend to be On/Off type devices... And they are usually sized, at least as large, as the maximum "uncontrolled" charging source...

The diversion controllers I'm aware of, like the morningstar tristars are not on-off devices. They use the same PWM signal for diversion load as they do for battery charging. But instead of sending the PWM to the battery they send it to DC resistors. So you get exactly the same smooth charging profile from these controllers as you would when they're in "solar" mode.

BB.

Re: Diversion Heater - Relay Setting

I would argue that charging/no charging (series controller) is different from charging/maximum discharge (diversion controller).

The diversion controller has to "micro cycle" the battery bank to "average" out net zero charging energy to a full battery bank. A series controller only has to turn off current to average net zero charging to the battery bank.

-Bill

Eric L

Re: Diversion Heater - Relay Setting

I thought that some charge controllers can be used as diversion controllers, and I thought that their frequency and voltage control were similar in either mode.

Just to expand on what Coot mentioned above, the Midnite Classic controllers have an AUX function which has a (fast) PWM mode that can signal a solid state relay to vary the voltage precisely as needed to maintain the charging cycle. Chris Olson started a thread on this here.

It only works with something, such as a resistive heating element, that can take a constantly fluctuating voltage input. But it does work well with large loads without introducing the constant cycling problems discussed above.

Cariboocoot

Re: Diversion Heater - Relay Setting

Gbridgem wrote: »

It has occurred to me that the mechanical relay I installed to control the diversion heater is a bit of a clumsey device for this purpose. As this is simply on and off, I will always get the cycling when I am on the edge of having enough power to operate it. Adjusting the settings may reduce cycling at the cost of some production.

Am I correct in thinking that I would not get on / off cycling had I installed a solid state relay? The relay would prorate the power between the batteries and the relay to hold their charge at the float coltage. A smoother diversion control process?

Guy

Solid state relay is still either on or off (you hope; otherwise the semiconductor is leaking outside of specifications). The advantage over mechanical relays is that there are no moving parts, lower operating current, and no contacts to arc when switching.

To achieve 'smoother' control you need to be able to vary the resistance of the load, either linearly or in increments. That requires more complex circuitry.

Gbridgem

Re: Diversion Heater - Relay Setting

When I first actived the AUX Fcn, I inadvertently put it on diversion SS causing the mechanical relay to chatter. It also displayed a % that moved up and down - making me think that the cc was regulating the amount of power it diverted to the heater as opposed to 100% on or off with the aux diversion: SS setting.

Seemed to me that the FM60 aux Fcn would work more seamlessly with the aux diversion: ss Fcn as opposed to the aux diversion: relay Fcn. Also the relay setting mentions suitable for hydro and wind (not solar).

Guy

gww1

Re: Diversion Heater - Relay Setting

Eric L
I also have followed chris's post that you linked to. I understand that the midnight classic has a pmw mode divertion. When I read the outback fm60 manual, it stated that its auxillary mode is also pmw. I haven't had a chance to try it yet but have bought a ssr and intend to. I believe it can be set the same as the classic and should work the same (hope). I have the mx 60 charge controller. The whole Ideal is not a full 2000 watt load at the exspence of the batteries but not to lose solar power that is being made with nowhere to put it.
Thanks
gww

inetdog

Re: Diversion Heater - Relay Setting

gww1 wrote: »

Eric L
I haven't had a chance to try it yet but have bought a ssr and intend to.

Not likely to be a problem if you got an even slightly larger than needed SSR, but be aware that the power dissipation in an SSR is at its highest while it is switching on and off. The max continuous current rating may not allow you to run an average current that high if you are switching at a high frequency.

gww1

Re: Diversion Heater - Relay Setting

Inetdog
I can't remember but it was either 470 volt or 600 volt, 25 amps. I am going to run 240 volts 8 amps through the inverter through ssr to hot water heater. I guess I will put a decent heatsink salvaged from a TV on the ssr. Thanks for the advise.
gww