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Battery maintenance (float) charger?


jamouton
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Reading the owners' manual, I see that they expect that if a C-MAX is left sitting for more than a month, the low-voltage battery may be discharged.  Well, I often go away for more than that, and I have used float chargers -- just maintain the battery at full voltage, don't actively charge it up -- on my other cars. 

 

Is it going to be OK to use a float charger on the C-MAX?

 

Jerry

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I'd think it's fine. The 12v battery is a standard lead-acid car battery. The biggest oddity is that it's in the rear, just behind the high voltage battery. But there's connection points under the hood for jump starting, you should be able to connect a float charger instead and be all set.

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Why does the C-Max need the 12v battery?

 

The easiest answer is electrically all of your C-Max, except for the electric traction motor and battery, is just like any other car Ford makes...it's all 12VDC.    It is technically possible to put a transformer on the traction battery to reduce the voltage to 12VDC but that would add weight and complexity while eating usable space.  Transformers are very inefficient, as in they waste a lot of power converting one voltage to another, put off significant heat, and are heavy.  That transformer would be required to run constantly to power your electric power steering, lights, radio, A/C and anything else electrically powered. 

 

And If you needed a jump start it would take a source as big as the traction battery to jump you off...forget about calling AAA. :)   It isn't really practical from either an engineering or cost view point currently...

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I have an electric scooter with a 96v lithium battery. It has a built-in DC-DC converter to provide power to all the usual 12v components on a motorbike, like the dashboard, signals, and headlights. Honestly, I think the DC-DC converter would be lighter than a 12v lead acid battery, though it's probably also marginally more expensive. But there also has to be an alternator of some sort, to charge the 12v battery, adding more weight and cost.

 

The decision to use a 2nd battery is probably more one of reliability: there's safety circuits that will disable the traction battery if something looks wrong, and the car can still drive if that happens.

 

But jump starting raises an interesting question. I was thinking that there was no 12v starter motor on the C-Max, that it used the main electric drive motor and the transmission to rapidly start the engine (that's why you can't start the engine when you shift into neutral). But if you can start the engine without the traction battery, then there must be a conventional starting system for the gas engine. So what do we actually have?

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But jump starting raises an interesting question. I was thinking that there was no 12v starter motor on the C-Max, that it used the main electric drive motor and the transmission to rapidly start the engine (that's why you can't start the engine when you shift into neutral). But if you can start the engine without the traction battery, then there must be a conventional starting system for the gas engine. So what do we actually have?

 

My understanding is that there is no starter of the traditional sort.  Starting is handled by the motor generator located in the transaxle case (there is also a larger traction motor that also provides regenerative breaking).  My further understanding is that the 12v battery powers the control circuitry required for the transaxale to work and that is the reason the car won't operate without a good 12v battery.

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The decision to use a 2nd battery is probably more one of reliability: there's safety circuits that will disable the traction battery if something looks wrong, and the car can still drive if that happens.

 

Does this mean if we disconnect the C-Max's high-voltage battery, the car can still be driven?

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