Bi-Directional DC-DC Confirmation

**IamIan** · 08-02-2006, 11:21 AM

I freind of mine forwarded me an Email he got from Ford about thier Hyrbid SUVs.... Most of it wasn't new and made sence.... the part I copy and pasted bellow made me wonder though ...

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One more note: If the NiMH battery gets too low to start the ICE, locate a small switch on the left foot well inside kick panel under a cover. It can be switched on and the 12 battery will start to charge the HV battery pack. There is an 8 minute timer so the 12 volt battery won't go dead. It can be recycled on as many times as you need to until the HV battery pack can start the SUV. Once it starts let the SUV run so that both batteries get recharged. Your scan tool will show you SOC. Use a charger on the 12 volt during this process. Great idea! Honda and especially Toyota need this feature.
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While I myself am not interested in driving a SUV of any kind Hyrbid or not...

I am trying to find out if this is true that the DC-DC is bidirectional and will let Ford Hybrid SUV Owners have a what looks like a very easy way to put a booster battery or grid charge on thier Hyrbids as from this they come with a factory way of charging the High Voltage 330V Hybrid BAttery Pack from the 12VDC Battery which is easy enough to charge with a 12V Lead Acid Battery charger....

I am just wondering if anyone can conferm this one way or the other.... the only thing I have been able to find so far on web searches is that it doesn't seem to use a back-up 12V Baised starter when the Hybrid battery is low as the Insight , Civic , Acord , Priud all do.

thanks to anyone who can conferm either this email I was forwarded or the suspitions that I have that it it not true.

Rick · 08-02-2006, 08:14 PM

I've never heard of that, but that would be a cool feature to have! And for potential modifications in the future.

Mike Dabrowski 2000 · 03-03-2008, 07:22 PM

The ford hybrids do have a 12V to 330V dc/dc just for that situation where the HV pack can't turn over the engine.
I saw it demonstrated in one of the hybrid classes.

Calpod · 03-04-2008, 12:28 AM

I have an Escape Hybrid, I didn't know that, but I will check next week.

Mike Dabrowski 2000 · 03-04-2008, 01:58 AM

I just looked at the slide from the seminar.
Ian"s detailed description is 100% correct.
I would expect all model years to have the same system?

**gpsman1** · 03-06-2008, 05:03 PM

Hi Mike. I'm the lucky owner of a 2005 Ford Escape Hybrid, and I have "Detailed Files" on this car.

The 12v to 330v "jump start" switch is very limited:

The Jump Start button does nothing if the HV battery has enough SOC to start the car.
The input ( human request ) from a button push is normally ignored, even though the LED lamp lights.
The HV battery SOC must be at a very low level, and this level is below 20% SOC.
20% SOC is strong enough to start the car.
Pressing the "jump start" button only rasies the HV battery to this minimum level, not past.
I have one reference that says this button "heats the battery" rather than directly charges it.
The FORD HV battery has built-in heaters.
If you buy a 120vAC engine block heater, you also get a 120vAC to 24vDC transformer that sends 24v into the battery to warm it. The battery heater is thermostatically controlled, and goes on when the battery is less than 50'F, and shuts off when the battery reaches 60'F. The block heater has no thermostat and is always on.
The block heater is ~400w and the battery heater takes 75w. ( directly measured as 3A at 24.5v )

I have not confirmed, but my hunch is, the 12v "jump start" only uses 12v to HEAT UP the battery pack, and does not apply a direct charge. The wire size ( 20ga I think) indicates only low 12v wattage to be possible. Heating the battery will increase the voltage, and available current temporarily, will it not? I say this because there are references in Ford documents that say this button is likely to be used only in very cold weather, or of the battery had sat unused for more than 30 days.

Can I help you guys with any other Ford Hybrid questions?
-John
( Still shopping for an Insight.... )

**IamIan** · 03-06-2008, 05:36 PM

Quote:

Originally Posted by gpsman1

I have not confirmed, but my hunch is, the 12v "jump start" only uses 12v to HEAT UP the battery pack, and does not apply a direct charge. The wire size ( 20ga I think) indicates only low 12v wattage to be possible. Heating the battery will increase the voltage, and available current temporarily, will it not? I say this because there are references in Ford documents that say this button is likely to be used only in very cold weather, or of the battery had sat unused for more than 30 days.

Can I help you guys with any other Ford Hybrid questions?
-John
( Still shopping for an Insight.... )

Any Battery has reduced capacity the colder it gets... the colder the battery the slower the chemical reactions that give you the electricity back out.... some battery chemistries are effected by this more so than others.

I do not know what the vehicle does... but it seems to me that just heating the battery instead of trying to charge it is just silly.... unless the Battery is nearly full in its SoC.

If you try to charge the battery any current you pass into the battery either goes into recharging the battery which is an exothermic chemical process for NiMH which means it gives off heat... and / or any current you pass will directly generate heat from the batteries internal resistance.... as a NiMH battery reaches higher SoC more and more of the electricity supplied to the battery will be converted to heat...

Also if the High Voltage battery were drained / near the bottom of its SoC no amount of heating will help it... you would have to give it some charging ....

It shouldn't be too hard to test I would think... a current sensor should be able to tell you if any current is going into or out of the battery... unfortunately that means high voltage work which always risks voiding warranties and killing the car or you... If it truly is limited by temperature.... I wonder how easy it would be to fool the temperature sensor?

**gpsman1** · 03-06-2008, 07:03 PM

Quote:

Originally Posted by IamIan

I do not know what the vehicle does... but it seems to me that just heating the battery instead of trying to charge it is just silly.... unless the Battery is nearly full in its SoC.

Maybe I wasn't clear. I'm telling you what the car does.
It does heat the battery. This I know for sure. This I have measured.
I have not put an ammeter on the HV battery while the jump-start button is pressed.
So I do not know if it applies high voltage and heating at the same time.

Also, if your cell phone dies on a cold day, put it near your body ( inside your shirt ) and warm it to close to body temperature. You will now get 5 to 10 minutes of extra talk time. Did your body "charge" the cell phone? Of course not. You just made the chemical reactions work better. I once was in a bind, away from home, without a wall plug and my laptop battery died. I needed desperately to copy files onto a USB drive. I took out the battery, and put it in front of the heater ducts in my car ( 100'F ??? 115'F??? ) for about 10 minutes. Then, surprisingly, even after needing to reboot the whole computer and spin up the drives and everything, I got about 15 more minutes out of that laptop... enough time to get all my files on to the external drive. The battery was so low to start with, it shut itself down and would not let me restart before.

Heat ( in moderation ) helps a battery more than you may think.

Also, in the Fords ( and probably yours ) there is a nearly linear drop in current output vs. temperature drop.

You get about 70 amps output at 95'F, and you get 45 amps output at 30'F.
( going by memory here, I have charts with the exact numbers, but not with me now )
-John

Armin · 03-07-2008, 10:26 AM

Wouldn't it be much more useful to have push-button activation of the regular DC-DC converter to charge a dead 12V battery from the high-voltage one? Many of us (myself included) have been in the situation where a dead 12V battery prevented starting the car. It's much easier to inadvertently drain the 12V battery! I've never had a dead HV battery prevent starting the car.

Caveat: In Insights the car can start off of the 12V starter, which it does at low temperatures, but has anybody ever seen this happen in warmer weather where it would presumably triggered by low charge in the 144V battery? I guess this supports Johns observation that that ominous button really only triggers a heater, not a charger to the HV pack of those other hybrids. That makes perfect sense since extreme cold is the most likely scenario where a car that doesn't have a 12V starter would fail to start.

**gpsman1** · 03-07-2008, 11:25 AM

Correct. There is no 12v starter in Ford hybrids. In there in a Prius?

I am happy to learn there is a 12v starter in the Insight.
When the salesman told me there was, being a Ford owner, I thought he was full of B.S.
Seems redundant at first, but now, I am happy the Insight does have that.
Since I want to buy an 8 year old car, it is comforting to know I can (probably) still drive when the IMA battery finally goes kaput.

Lets say for argument the Ford HV battery can only output 15 amps at -20'F.
Let's also say this is not enough to start the car.
You have a 12v battery on board, but there is no 12v starter.
It is confirmed there are HV battery heaters built-in to the pack.
Lets say for argument the 12v battery can raise the HV battery to 0'F in 8 minutes.
Let's say the HV battery can output 30 amps at 0'F and this is enough to start the car.

I do not consider this "charging" the battery.
But for lay-man speak, Ford calls the button a "jump start button" in the owner's guide.
For the lay-man, it seems to be a "charger".
For technical minds, like those around here, it is not really a charger, now is it?

-John