Hi, I've got a Generac Guardian 10kW generator as backup for my off-grid PV system. The generator specs recommend a thermostatically-controlled battery warmer and crankcase warmer where temperatures regularly fall below 32 F, and here in central Ontario we often fall below 5 F. My only concern is that this would put a constant drain on the batteries at such temperatures. Does anyone know what the load would be for such warmers? My guess is that I'll just have to accept this as good insurance for cold weather power. Thanks, ...Terry

I have a warmer on our VW diesel, a battery warmer is usually about 60w and we have a 1000w coolant heater. My guess it is a smaller stick on heater in the 50-100w range. Seems odd you would need those unless your below 0F. I would skip the battery warmer and add a smart battery maintainer, it will keep the battery in good shape and charged, it also slightly warms the battery. Keep synthetic oil in the genset and it won't care as much about cold temps and won't break down over time as fast.

I agree - I'd use a fully charged battery sized for the temperatures, synthetic oil and make sure that the generator runs for awhile after it starts before it sees load.

Thank you for that feedback, Brock and Jon. We do regularly get below 0 F in January and February. Fortunately we do have a battery maintainer, although I don't know how smart it is. I'll be putting synthetic SW 5-30 in it as well. So one approach is to just ensure it runs for a while before it sees load, but myGenerac Guardian in auto mode (signaled by my Magnum auto gen starter) only warms up for 5 seconds before seeing load. The only way I could change that is to do a manual start in 0 F days, trudging out to the back of the house through the snow to start it -- it would take me a few minutes to get back to the electrical room and transfer the load, enuf to warm up the generator.

Perhaps the best thing would be to put in that battery warmer but add a switch to it that I manually flicked on when I'm expecting those below-0-F temps. Wish I could just change the thermostat built into the warmer instead to be 0 F instead of 15 F or whatever it is. Or change the genny's 5-second warmup to something longer, but that's hardwired.

Or maybe I should just stop being a crybaby, warm up my snowshoes, and stick with manual starts, simplifying the system!
...Terry

Can you get it to send the start signal while the actual load is off? Is it an auto transfer switch or ?

I don't think I know enough about this to understand your question, Brock. The inverter's auto generator starter (http://www.magnumenergy.com/Doc-Lib-AGS.htm, standalone) detects a low battery voltage and sends a start signal to the generator. The generator's remote startup logic starts the engine and waits 5 seconds before sending power to the inverter. The inverter sends this to the battery charger and the house load.

Oh, I believe you can set how long the Magnum takes to transfer as well once it sees a stable voltage. At a minimum it will be about 20 seconds until the inverter see a stable input. It has to be flat for that long for it to sync up and then transfer. Even once it transfers, the Magnum should then ramp up charging depending on what loads are present.

You should be good to go and again I would just put a trickle charger on the battery and nothing else since you have an inverter already in the mix

That's great news, Brock -- thanks!
...Terry

Consider an AGM battery - it should be fine with a slight trickle charge. You could also use warmers for battery and generator but control them so they only come on in bitter cold weather.

Maybe you could put a manual start switch inside - work but at least it's warm work. Full load out of a 0F generator 5 secs after starting isn't very good for the engine - although a crankcase heater helps some. Engine oil starts to lubricate well around 160F. But this wear issue is unrelated to a starting battery warmer - I believe than an oversized or an oversized AGM battery fully addresses that issue without wasting energy.

Most commercial emergency and stand-by power generators maintain a block temperature of ±100° to 110° and are required to go to full load in the 5-9 second range...that is what they are designed to do.  If you are not going keep the block warm, you should disable the 5 second transfer and convert it to manual to avoid possible engine damage.  Not following the mfgr's recommendations may void your warranty, however.

Bruce

Bruce you are correct. The catch is in this situation his inverter will trigger the genset to start due to a low battery situation, and then the inverter will have to see a stable voltage, typically +/- 1 hz and stable voltage to lock on, usually not varying more than 1% or 2%. It has to see that for a minimum of 30 seconds to lock. So as the genset warms up it might fluctuate a bit push the 30 seconds out longer before the inverter will sync up and start demanding power from the genset. With most inverters you can set the sync time or transfer time longer on the inverter itself, say for a stable 60 or 120 seconds. You usually cannot however change it shorter than 30 seconds. During this time the inverter is still supplying power to the loads via batteries and most inverters also have a max draw rate from a genset, so if the loads are using the total capacity the inverter it won't try to change the batteries at the same time, but rather wait until the loads decrease then start to charge the batteries.

Bad news, Brock, my inverter manual says "After the AC input power is qualifi ed (approximately 15 seconds), the incoming AC power will transfer through the inverter". And unfortunately there isn't a setting on the inverter to extend this 15 seconds. Guess I'll just wait and see if the battery maintainer and synthetic oil do the trick...

Bummer on not being able to set it out longer. I looked on my Xantrex 6048 and you can set the time out longer, oh well.

You could go with a simple delay unit. Basically it starts counting when it sees power then turns on. They come in all different times and you can even get adjustable ones. I use them to stagger when motors come on so my inverter doesn't get with with them all at the same time. The trick is they are rated like 10 amps at 120v, so I use one to control a 50 amp 240vac contractor. You could just put that between your genset and inverter.

I expect that Brock's suggestion would pay for itself many times over in reduced engine wear. If they are expensive, I'd probably build one with a $10 igbt.

The time delay relay I am talking about is this one

http://www.icmcontrols.com/products/category.php?cat_pk=12

commonly refereed to as "delay on make" controllers, search for that on ebay, I got mine for about $10 each. Then I just used a standard contactor, just make sure it is 240 vac and rated for what ever the genset can put out (I would double it).