# Accessory Battery



## maiku (Jun 1, 2008)

Would a single 12V accessory battery be enough to power all necessary stuff?
I'm looking at just using one high Ah 12V battery with a voltage regulator to keep constant 12V to power the brakes, steering, heater, lights, radio, basically anything in the car that needs 12V

maybe install a permanent 12V battery charger than would take the same 110V line as the pack charger

this removes the need for a DC-DC converter and leaves more power for the motor


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## Coley (Jul 26, 2007)

I put a 95AH marine deep cycle, 12volt battery, in my car for the car system battery.

Using the headlights, wipers, radio and all stop/turn signals, it still took 20 days of daily driving, to pull it down to a SOC of 90%.

A 225 AH battery would be good, if you have high amp draw like a stereo, etc. A volt meter just for it, would be a nice addition to the dash.

An EV system battery doesn't need high CCA to do it's job, just good AHs.

And it saves the cost of a DC/DC expense.


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## adric22 (Jan 17, 2008)

I used a 33ah wheelchair battery. It is a very small 12V AGM about the size of a lawn-mower battery or something similar. I rarely drive at night, but even on tests where I had everything running: Lights, stereo system, etc.. It barely affected the SOC. Then again, my car only has a 20 mile practical range so the traction pack is always going to run out before the 12V battery will. It saved me from having to buy a DC-DC converter and I'm using a little $18 charger I bought at wal-mart that is connected to the car's main power inlet along with the traction charger.


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## maiku (Jun 1, 2008)

obviously i'm only going to use a battery that can last the drain as far as i'm hoping to drive (roughly 50 miles)

i guess maybe an exide orbital 50Ah should do the trick
it's only 40lbs and should be enough to power all 12V


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## ww321q (Mar 28, 2008)

maiku said:


> obviously i'm only going to use a battery that can last the drain as far as i'm hoping to drive (roughly 50 miles)
> 
> i guess maybe an exide orbital 50Ah should do the trick
> it's only 40lbs and should be enough to power all 12V


Any thing that is deep cycle , AGM , or Gel . No car cranking batteries . I found out about that when my truck was new and I was running an inverter to run tools on . J.W.


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## favguy (May 2, 2008)

Yep, sounds good, that's exactly what I'm planning to do. 

You need to add up the current draw assuming night time driving in bad weather, so include all lights, blower motor, contactor load, wipers, radio. Also allow a percentage of the current (I used 10%) of the indicators, brake lights, brake vacuum pump running, heated rear window element. 

When you've got the total current for that lot, work out the maximum time your car is likely to run on a slow trip until its maximum range has been done.

Use the battery wiki to calculate the Ah you'll need to run that current over that time allowing for a maximum dod of about 60% 

I worked out that 100Ah would be fine for mine.


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## VDubber (Jun 2, 2008)

I once had my alternator in my ICE go out (completely). Being that you almost have to remove a driveshaft to replace it (crazy engineers), I simply grabbed one of the deep-cycle AGMs that I use in my 'electric' fishing boat.

It would run the car for quite a bit before needing charging, a couple days even. But I didn't like the slow heater fan, dim lights (both inside and out), and brownish headlights that result from running a bunch of 13.8V-14.5V accesories at 12V.

If I was not using a DC/DC, the next best thing might be using a 14V battery (racing battery or 6+8 pair). Of course that can cost almost as much as a converter...


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## adric22 (Jan 17, 2008)

VDubber said:


> But I didn't like the slow heater fan, dim lights (both inside and out), and brownish headlights that result from running a bunch of 13.8V-14.5V accesories at 12V.


Keep in mind that if you change out all the lights in your car to LEDs then it will really cut back on the power you use. For example, I used to draw about 8 amps of power just by running the parking lights, brake lights, and interior lights. I was at about 14 amps with the headlights on too. But replacing everything with LEDs brought that down to under 1 amp for all of the lights except the headlights. When running those I was at about 7 amps total. However, they aren't cheap. Expect to spend about $150 changing them all out.


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## VDubber (Jun 2, 2008)

adric22 said:


> Keep in mind that if you change out all the lights in your car to LEDs then it will really cut back on the power you use. For example, I used to draw about 8 amps of power just by running the parking lights, brake lights, and interior lights. I was at about 14 amps with the headlights on too. But replacing everything with LEDs brought that down to under 1 amp for all of the lights except the headlights. When running those I was at about 7 amps total. However, they aren't cheap. Expect to spend about $150 changing them all out.


That's good advice, and the mega lifespan of the LEDs pretty much pays for themselves. But how would it change the slow fans and dim headlights?

Auto bits are intended for the 13+ volts that a running car has in it's system - not 12V. You can run them at 12V just fine, but at a lower performance. Some people don't mind, but then there is a potential safety issue with the headlights and brake lights.


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## adric22 (Jan 17, 2008)

VDubber said:


> But how would it change the slow fans and dim headlights?


Well, to be honest, I've never noticed these issues. Then again, when I bought the donor car it was never running to begin with so I never saw how these things acted at 13 volts. Still, the headlights seems perfectly bright to me. Since the vehicle doesn't have a working airconditioner I haven't really messed with the fan much, though I have turned it on. I usually roll the windows down (they are power windows too!) 

However, it may vary from vehicle to vehicle. For example, in my gas car, I've turned on the headlights before starting the vehicle and I do not notice them being brighter after starting. obviously they dim while the starter motor is turning, but afterwords it is the same.

Another possible issue is that various vehicles may draw more amps from the battery for all the different things being used and more amps lowers the voltage. Since I removed so much stuff from my car, about the only thing the 12V battery is running during a regular drive is some relays, the stereo system, and the instrumentation on the dash (which is all custom and very low power usage) At night about the only thing that consumes any power is the headlights. 

It might be interesting to see what voltage your vehicle is at while the headlights are on and the engine is not running. For my EV, I have a digital volt meter on the dash and it reads around 12.1 volts during a daytime drive and 11.9 volts when the headlights are on. I wonder if yours goes lower than that?


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## VDubber (Jun 2, 2008)

True, it is a old car and the wires may be aging. The voltage was 12.3 at the bat with the lights on, but 11.7 at the headlights.

This pops up another suggestion: When using a battery instead of a DC/DC, keep it close to the headlights (the single biggest user of 12V in a EV) and use nice fat juicy short wires and a relay if you want to get the most out of it.


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## Corvettemike (Jun 1, 2008)

Im a new bee so please excuse any stupidy I may be saying here. What about a double shaft on the dc motor and run a pully to an altenator and a 12 volt battery for my accesories.?


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## VDubber (Jun 2, 2008)

Corvettemike said:


> Im a new bee so please excuse any stupidy I may be saying here. What about a double shaft on the dc motor and run a pully to an altenator and a 12 volt battery for my accesories.?


This would work to charge the 12V battery, just inefficient. Alternators don't make very good chargers, and a separate 12V charger for the accessory bat seems cheaper then working up an alternator mount and all that.

But I still like DC/DC converters better. $188 doesn't buy much battery these days, anyways.


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## maiku (Jun 1, 2008)

VDubber said:


> But I still like DC/DC converters better. $188 doesn't buy much battery these days, anyways.


i think the point was to try and avoid using the pack voltage
i'm not sure how much of a draw it would cause, but with EV's, every little bit counts


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## adric22 (Jan 17, 2008)

VDubber said:


> This would work to charge the 12V battery, just inefficient. Alternators don't make very good chargers, and a separate 12V charger for the accessory bat seems cheaper then working up an alternator mount and all that.


I've actually seen two different vehicles where they were designed in this manner. However, I think it is a horrible design for many reasons. 


It is mechanically a lot more complicated to design and build
It pulls torque away from your motor, so you'll have less power for driving
Alternators are not very efficient so in the long run, you'll waste more power that way.
I prefer a seperate charger on the 12V pack, but a DC-DC converter is acceptable also. I don't like the alternator designs.


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## Qer (May 7, 2008)

maiku said:


> i think the point was to try and avoid using the pack voltage
> i'm not sure how much of a draw it would cause, but with EV's, every little bit counts


If your car is using 300 Wh/mile and you're going 40 MPH, that means the motor will draw 12 kW from your main pack. If you add head lights etc to that, it's maybe 12.2 kW instead. Add power steering and you might be up to 12.4, vacuum pump, radio etc might add a hundred Watts or so on top of that. So yes, it does affect the range but if you're going to pull hundreds of Watts from an auxiliary battery it has to be a serious battery -> more weight to haul around or less weight left for the main pack.

So in the end it doesn't really matter. Everything that chews electricity will affect the range, directly or indirectly and all the power you use up will have to be stored in lead (or if you have the budget, Lithium). Having an auxiliary battery is technically simpler and probably cheaper but will mean a Voltage that's slowly degrading during the discharge which will mean less light from the head lights (try to use the main lights in the darkness on an ICE-car with and without the engine running).

Having a DC/DC-converter instead means that all the lead weight can be put in the main pack so depending on the situation it might actually give you more range (although not much more) and better light from the head lights, but instead it's a technically more complicated and expensive solution. However, you should still have a small auxiliary battery (like MC-size or so)! You don't want the car to black out if the DC/DC dies on you.

Going for a battery or DC/DC is a design issue, really. Both have cons and pros. I do lots of driving in the dark (approximately 4 months are pitch dark when I go to and from work where I live) and I just can't stand bad head lights (that's when you smack on huge extra lights quicker than quick around here). If you live closer to the equator it's probably not an issue for you. YMMV, as they say.


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## maiku (Jun 1, 2008)

i guess the minute amount of wh taken from the pack from a DC converter isn't that high
maybe it's better to use a 12V during daytime and DC/DC at night


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## desiv (May 20, 2008)

Just a question.
If you use a DC/DC, do you also need to charge the 12V when you charge the main pack, or will the DC/DC give you enough voltage to not have to charge the accessory battery when you charge the pack?

desiv


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## VDubber (Jun 2, 2008)

desiv said:


> Just a question.
> If you use a DC/DC, do you also need to charge the 12V when you charge the main pack, or will the DC/DC give you enough voltage to not have to charge the accessory battery when you charge the pack?
> 
> desiv


Many of the DC/DC converters offered for EV use will output 13.8volts - this is a good voltage to float charge a 12V SLI battery and matches an alternators output.

You can use a cheap 12V motorcycle starting battery, since it is only used to fire up the controller/contactors and for emergency backup. It also helps smooth out any current spikes from starting smaller motors (aka the heater and wipers). Just hook the converter to chassis ground and the battery's positive terminal. Then hook the battery up as usual to the car. Think of the converter as a solid state alternator


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