Cordless Block heater - PeachParts Mercedes-Benz Forum

Chad300tdt · #1 12-22-2008, 10:39 PM

I've been considering putting a deep cycle marine battery in the trunk of my CD with a power inverter and a timer to hook up the block heater.

I'm thinking this could allow a 1-2 hour preheat with the block heater before my wife leaves work. With the temps getting lower I want to make her diesel experience as easy as possible.

I'd put the battery on a charger overnight when she got home so the battery would be fully charged for the end of the next work day.

Any reason this wouldn't work? What would be the best power inverter to use? What deep cycle battery would you recommend?

Matt L · #2 12-22-2008, 10:48 PM

At 300 watts and a 100% efficient inverter, that's 25 amps from the battery. 500W is nearly 42A. What size heater do you want to run?

Of course, the inverter is not 100% efficient. Figure 85% and add that to what you need for two hours. A standard group 31 AGM battery should do the job just fine, and would probably run for more than one winter. This will cost you about $150. I do not know where to buy big inverters such as this, but boat shops should carry it (as well as the battery).

A set of smaller cells to provide 100V+ DC could power the heater directly. That seems like a lot of trouble, and a charging circuit would have to become creative, but it would be more efficient.

Chad300tdt · #3 12-22-2008, 10:53 PM

It has the factory block heater. I don't know the specs.

I've seen diesel and propane pre-heaters, but they run close to $1000. I'd like to do something for under $500.

Matt L · #4 12-22-2008, 11:00 PM

With the engine hot, measure the resistance across the plug. It's probably a 400W unit. Divide the resistance into 120 to find the current, then multiply by 120 to find the wattage. Equivalently, divide V^2 by the resistence (120*120/R).

Note that inverters have two limits, VA and watts. VA is volts * amps, and always VA >= watts. The VA rating is usually what is listed in big letters, the watt rating must be found in the specification. VA differs from watts when the load in an AC circuit is inductive or capacitive. Your heater is neither, so watts = VA, and you must buy a heater that supplies both 400VA *AND* 400W. That will probably be a 600VA unit, or higher.

pawoSD · #5 12-22-2008, 11:18 PM

Why spend all that money and effort....a properly tuned engine with a good starting/charging/battery/glow plugs should easily start down to -10F.....you're only in PA, not Antarctica.

It gets ultra cold around here and our cars have had no issues. In fact its only 6F outside right now!

redassag00 · #6 12-22-2008, 11:20 PM

Why not hook wires to it so the car could charge the battery on her commute?

Chad300tdt · #7 12-22-2008, 11:26 PM

The CD took 12 seconds of cranking this morning in 5˚ after 2 glow cycles and 3 seconds in 12˚ this evening after 2 glows.

I just changed the plugs, reamed the chambers, adjusted the valves and rack damper, changed the oil/filter, fuel filters, air filter. The only thing I still want to do is the injectors (it leaves a soot spot on the ground from the time spent warming up).

It does get to below 0 in the middle of winter here and I'm not sure the CD will benefit that much from tuned injectors.

Chad300tdt · #8 12-22-2008, 11:27 PM

Quote:

Originally Posted by redassag00

Why not hook wires to it so the car could charge the battery on her commute?

I thought of that, but wouldn't I need a bigger alternator?

pawoSD · #9 12-22-2008, 11:37 PM

Injectors do make quite a bit of difference, I forgot to mention I have 1.5 year old Bosio nozzles in mine...made a very big difference.

Soot on the ground when idling/warming up is normal. Mine does that too.....when the engine is real cold and idling the combustion isn't that great, so it makes more soot.

Jeremy5848 · #10 12-22-2008, 11:43 PM

The standard factory block heater is 400W or about 3.5 Amps at 115 VAC. If you wired eight (8) 12 volt batteries in series you would have a little over 100 Volts; the block heater would draw about 3 Amps at that voltage or about 300 Watts. That would heat the engine at Pennsylvania temperatures in about 4 hours, maybe less.

To be able to draw 3 Amps for 4 hours, you would need 12 Amp-hours but the battery would need a much higher rating to not be totally exhausted at the end of 4 hours. I would recommend a battery with a 20-hour rating of 3 Amps, which is a 60 A-H battery. That is the size of a small car battery. You would need 8 of them. That would power the block heater without the loss of an inverter.

A timer to work on 12 Volts DC is possible; I don't know how reliably an inverter made for 60 Hertz sine wave AC will work on the hash that comes out of the typical small, inexpensive inverter.

Wiring would not be difficult. Use 16 gauge wire, insulate it heavily and fuse both leads coming off of the battery pack. Make sure the batteries are securely mounted so they don't tip over or short, one to another.

Charging the batteries is another matter. It will take a fancy switch setup to change the batteries from series to parallel so a standard car batter charger will work. You might be better off building a charger that will produce about 120 Volts at 5 Amps or so to recharge the batteries overnight.

Interesting project. Happy to discuss this further with you.

Jeremy

Chad300tdt · #11 12-22-2008, 11:55 PM

Wow the cost of 8 batteries alone would make a propane preheater an affordable option.

Here's one whunter linked in another post:
http://www.servicemate.com/catalog/partdetail.aspx?PartNo=LP6500-12V

redassag00 · #12 12-22-2008, 11:59 PM

Forgive my ignorance chad, why arent you hooking the block heater to a cord with a timer and plugging into the wall?

Chad300tdt · #13 12-23-2008, 12:03 AM

Quote:

Originally Posted by redassag00

Forgive my ignorance chad, why arent you hooking the block heater to a cord with a timer and plugging into the wall?

I can do that at home, but I want to have a preheat option for the parking lot at my wife's place of employment so when she goes out to her car at the end of the work day, she can easily start the CD. She often works 10 hour days and the car sits all day in the cold and even gets a few hours of sitting after the sun goes down and the temps start really dropping.

redassag00 · #14 12-23-2008, 12:18 AM

Ahhhh I see. Same issue with me, at work I start cold...

raslaje · #15 12-23-2008, 12:32 AM

Why not a remote starter and your wife can activate it a couple times during the day and heat the interior for her too?