Two Battery Extreme Cold Weather Engine Start

261

02:22:51

Simulator does not like the two parallel connected batteries but should work fine in vehicle.

Top lamp is starter motor at 300 amps.  10 amp current source is car alternator at idle speed and current output amperage tops about 1500 engine rpm.

Cut out switch on each battery to charge with alternator each battery with top battery to assist cold starts bottom battery being the run battery with the alternator after the engine is warmed up and running.  Vertical switch at bottom goes to vehicle ignition and electrical systems.

Note output from the alternator goes through both cut out switches ( probably knife switches or able to handle high currents.

published 9 years ago

2ctiby

9 years ago

You are right about EC not liking two batteries together in parallel.....here is a little work around which should make your circuit here work nicely:

2ctiby

9 years ago

Just put a 1 ohm resistor in series at the lower battery positive terminal

thebugger

9 years ago

Voltage sources in parallel is usually not a good idea, unless the currents (therefore the voltages) through them are evened. Otherwise the voltage difference will cause current to flow from the higher potential to the lower, and in case of car batteries where the internal resistance is very low it may cause one battery to overheat until the voltages even out. That's why before putting them in parallel both must be either completely dead or fully charged. After that it's no problem.

lmccoig

9 years ago

Thanks for the one ohm resistor tip. Probably best with engine stopped to pull one cut out switch to stop battery discharge current flow.

hurz

9 years ago

1Ohm at 12V for 300A, LOL

2ctiby

9 years ago

@Hurz, like I said....the 1 ohm was just a quick workaround to get the EC to work.

thebugger

9 years ago

And as i said it's not a workaround. In reality current will flow through non equalized power sources when in parallel

2ctiby

9 years ago

In real life, two similar batteries can be placed in parallel providing they are in a compatible state. My 'workaround' was just to get rid of the EC non working presentation so that he could at least alter his circuit and make a real life starting point. It was not meant to be a working practicality.....that's why I called it a workaround rather than simply suggesting that it would be a suitable entry....I suppose the word 'workaround' means different things to different people.

2ctiby

9 years ago

With car batteries, it is commonplace to jump start a car which has a poor battery by using a good similar V battery. That is putting them in parallel, so your phrase 'must be' is not appropriate.

thebugger

9 years ago

Yes, i know, and current does flow from the more charged battery to the discharged one. In real life power sources can never be fully matched, so current will always flow from one to the other when in parallel. The thing that matters is the potential difference of the two sources and the internal resistance. Let's say we have an internal resistance of 0.5ohm and a potential difference of 3V. Then the current will be I=U/R I=3/0.5=6A

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