Cold start with two batteries. 1

[pauljohn]

I vaguely remember reading that in a cold start situation with 2 available batteries you get more power if you heat one battery using the other then start the engine with the warm one rather than simply connecting them together.

Is this true and what would be the best method of heating?

Thanks for any help.

Paul

 

[swall]

How cold is cold?

 

[kenvlach]

This is technically true if the cold battery temperature is < 10[sup]o[/sup]F and if you can use one to heat the other to 80[sup]o[/sup]F.

You will need a dual (parallel) battery setup (that avoids draining the primary when engine is off). The primary battery is placed on some rigid polystrene for bottom insulation and wrapped in electrical resistance heating tape (the kind used to melt snow on eaves & keep pipes from freezing). The heating tape must be able to work off 12 VDC. The top is left as-is to avoid hydrogen buildup.

I considered one when I lived in Wisconsin, but I never had enough room under the auto's hood & didn't want to mess with the electrical. Similar to the 120 VAC battery warmer on the JC Whitney site:

http://www.jcwhitney.com/autoparts/...ku=battery+warmer&searchbtn.x=4&searchbtn.y=8

Carried a spare battery around for a while to do my own jump-starts, but eventually bought the highest CCA-rated battery that could physically fit.

For more info on dual battery systems and the effect of temperature on (lead-acid) batteries, see

http://www.uuhome.de/william.darden/carfaq7.htm#ccatemp

 

[pauljohn]

Thanks for the info kenvlach

 

[rmw]

Back in the old 6 volt days, I would take the battery out and bring it inside the house and put it by the hot water heater (the rest of the house had he heaters turned off at night) so that I could get my car started in the morning.

If I left it out in the car (temperatures about or just below freezing) it would never start, but bringing it in did the trick.

rmw

 

[MikeHalloran]

In isolation, I'd be real nervous about using my only reserve energy store to heat the primary one in the hope of making it work better.

Install a third battery and thermostatically controlled heaters under all three.





Mike Halloran
Pembroke Pines, FL, USA

 

[Tmoose]

It looks like warming a hard working lead acid battery from 0 F to 68 F might boost available capacity about 50%. Not bad.

http://www.mycableshop.com/300x300/fig2.gif

 

[TheBlacksmith]

1) Buy the biggest optional battery that will fit.
2) Use synthetic oil.
3) Keep the engine tuned up.
4) Worry about something worthwhile.

This has never failed for me, including starting a 10.5 to 1 compression Olds 455 in -30 degrees in Buffalo, NY and an Olds diesel in -10 in Rhode Island.

Blacksmith

 

[pauljohn]

I was more interested in the theory of it than setting up a system. I assume the battery prefers the steady low output of the heat tape than the quick heavy output the starter would require, esp. when it is cold.

If this is true then gel-cells would suffer even more when it was cold. We use gels alot on boats and it might be worth sacrificing a couple of batteries and try to heat up the start banks in an emergency if we are having trouble starting in cold weather.

 

[MikeHalloran]

On a boat, you could fit a propane fired space heater. Propane turns to liquid at atmospheric pressure, and won't come out of the bottle, somewhere around ~-40F, but at that temperature you've got other problems.



Mike Halloran
Pembroke Pines, FL, USA

 

[kenvlach]

A 'trickle' charger will also keep batteries warm. The output should be set to no more than 1 Amp at 13.5-13.8 volts* (max) for all lead-acids (auto, deep-cycle and gel). If no AC is available, isolate one battery to power an inverter for the charger.

*A higher voltage is actually required for charging at very low temperatures, see graph at

http://www.lifelinebatteries.com/marinegraphs.php

but 'trickle' charging keeps the battery slightly warm, so don't use a higher voltage w/o some type of thermostatic shut-off.

What minimum temperatures are observed inside the boat?
Ocean water freezes at 28-29[sup]o[/sup]F, so below deck temperatures shouldn't get really cold.

 

[patprimmer]

Hydrogen gas collecting below decks could be an exciting issue if not addressed with suitable and thoughtfully implemented ventilation.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[pauljohn]

Mike
-40F! If I saw that temp I'd be heading south the same day. I like the propane heater idea.

kenvlach sea temps around 40. Air temp maybe 20. The boat doesn't have any charging problems.

Pat-The nice thing about gels is that they do not gas when charged properly. That's just one of the reasons we don't use lead acid anymore.

Normally there is no problem, the boat has masses of starting power - Four 8D batteries, and that is just the starting bank. The boat has two house banks of eight 8D's each. But owners don't like to be bothered with minor details like charging batteries! He accidentally parallelled everything and ran all the banks down over a weekend which got me thinking about the cold start problem.

 

[MikeHalloran]

Ah. You need switches that make it impossible to parallel all the batteries.

I worked a cold, damp evening on a boat that had been built for service on the North Sea. She had a domestic furnace in the e/r. Really took the chill off.



Mike Halloran
Pembroke Pines, FL, USA

 

[Ashereng]

A cold battery has less power than a warm one. Something about heat of activation or reaction or someother (see professor, I was awake ... sometimes).

When we shoot videos on the ski slopes, the battery quickly die. That is why the spare is usually in somone else's jacket (under the arm pit is good for warmth). We swap batteries. The cold one gets reheated up, and we cycle it around again.

 

[patprimmer]

Even when the remote control batteries go flat, you can get a short reprieve by removing the batteries and rubbing them vigorously in your hands. The extra heat generated will give you enough time to get replacements next day.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[unclesyd]

For the boat we just use 12V/24V starters on 32V systems. Just don't lay on the starter button. I've seen this system used on both coasts and along The Gulf.

One other setup is to have small gasoline ONAN genset hooked to batteries and use it to peak the batteries and at the same time warm them up. All it takes is simple knife switch.

 

[unclesyd]

Forgot to add the latest battery charging gadget. They seem to be working on two local boats and on motorcycle.

http://www.ctek.com/us/home.asp

 

[frankiee]

"..cold start situation with 2 available batteries you get more power if you heat one battery using the other then start the engine with the warm one"

I have also heard of using the headlights first to warm a battery internally before trying to start in cold weather.
I have pasted a link that would describe the theory better than I can.
In a nut shell, you would use the spare 12 volt to power a 12 volt heat blanket for the battery you plan to start.
The starting battery in theory would be able to outperform the 2 batteries put together at a cold temperature.
I don't know if this happens.
I have tried turning on the headlamps to warm the battery first but got little or no results.
In the article it says to "bootstrap"
I would be very cautious if I ever tried this.
It would have to be a do or die situation.
Would be nice to know for sure if it would work.

Anyway. A cold battery just dont flow amps.
Trick is to get battery warm some way.

http://www.motherearthnews.com/libr..._Starting_and_other_Cold_Weather_Battery_Lore

 

[bentwings1]

My Dodge Cummins diesel has 2 of the biggest batteries I could find and it turns over just fine at -20F with 15-40 Rotella in it. Batteries are in parallel and have cables as big as a good sized thumb. It takes about 10 minutes running to recharge from the grid heaters and the start. Belive me it takes some kind of power to turn this motor over at that temp. It's well worth it to spend a little extra on big batteries up here in the cold weather belt. You only need to walk once in this weather to learn this. After 3 years regardless of the warantee you get new batteries. Simple solution to a cold problem.
I well remember the 6 volt days. Even the early 12 volt batteries had a tough time at -20F. It would be nice to be able to plug the block heater in but out in the middle of nowhere it's just you and the batteries.
There's lots of tales of preheating the batteries, lots of them blew up as they outgassed, frankly if there is a doubt, add another in parallel. If you have to take them in the house, fine, it sure helps.