# [EVDL] Caution When Installing HV Accessories



## EVDL List (Jul 27, 2007)

Hello everybody,

This message started out as a question to the group last night, but I
figured out what I was doing wrong as I was writing the message. I thought
I would pass it along just in case it could help others.

While checking up on my car's charging last night, I noticed that the
relatively newly-installed DC-DC converter was making a soft "tick" noise
every 10 seconds or so. I thought that was really strange because it was
supposed to be off when the key was off and the car wasn't being driven.

I put a volt meter across its inputs and watched the voltage climb to around
100V. At that point, the converter would click on and the voltage would
quickly fall. Climb again to 100V and repeat.

At first, I was perplexed, until I opened up my high-voltage box and saw the
pre-charge resistor. I had installed the DC-DC converter positive input on
the output of the main contactor. Since the main contactor comes on with
the key, I thought it worked great to turn on the converter also. However,
I forgot about the pre-charge resistor and its job of keeping the contactor
output at pack voltage.

Bottom-line, I had caused two issues. First, the DC Converter was
continually draining off charge from the pre-charge resistor, so my battery
pack was being drained when I wasn't expecting it and stressing my
pre-charge resistor with constant current flow. Second, the pre-charge
resistor wasn't getting to do its job of keeping the controller caps charged
up so I wouldn't have a high current inrush when the contactor was
activated.

I now have a solid-state relay on order to have a separate enable switch for
the DC-DC converter off the key switch (without a pre-charge resistor!).
Until then, I have the manual disconnect off whenever I'm not driving the
car. No sense draining the pack and continuously switching the converter on
and off needlessly.

Reading through Mike Brown's "Convert It" book, he clearly goes over this.
I obviously missed that fine detail the first time!

I will obviously do the same thing for the new heater I'm getting ready to
install.

I know that many people have two contactors between the battery and the
motor controller. So far, I only have the one. I know that I'm missing an
element that could be a key safety factor if the main contactor welds
closed. I'm trying to figure out where I would put the second one. They
are big!

I hope this helps some other person with less experience avoid this mistake.

Mike


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## EVDL List (Jul 27, 2007)

> I now have a solid-state relay on order to have a separate enable switch 
> for
> the DC-DC converter off the key switch (without a pre-charge resistor!).
> Until then, I have the manual disconnect off whenever I'm not driving the
> car. No sense draining the pack and continuously switching the converter 
> on
> and off needlessly.

Make sure the solid state relay output is DC rated.

The AC rated ones are just an SCR, which means you can turn it on no 
problems, but can only turn it off when there is no current flowing.

If you did get an AC rated one, you could use it to turn the pre-charge 
resistor on.
once the contact or closed, the SCR current will fall to 0, and it can be 
turned off.

Matt

----- Original Message ----- 
From: "Mike Nickerson" <[email protected]>
To: "'Electric Vehicle Discussion List'" <[email protected]>
Sent: Thursday, September 23, 2010 12:24 PM
Subject: [EVDL] Caution When Installing HV Accessories


> Hello everybody,
>
> This message started out as a question to the group last night, but I
> figured out what I was doing wrong as I was writing the message. I 
> thought
> I would pass it along just in case it could help others.
>
> While checking up on my car's charging last night, I noticed that the
> relatively newly-installed DC-DC converter was making a soft "tick" noise
> every 10 seconds or so. I thought that was really strange because it was
> supposed to be off when the key was off and the car wasn't being driven.
>
> I put a volt meter across its inputs and watched the voltage climb to 
> around
> 100V. At that point, the converter would click on and the voltage would
> quickly fall. Climb again to 100V and repeat.
>
> At first, I was perplexed, until I opened up my high-voltage box and saw 
> the
> pre-charge resistor. I had installed the DC-DC converter positive input 
> on
> the output of the main contactor. Since the main contactor comes on with
> the key, I thought it worked great to turn on the converter also. 
> However,
> I forgot about the pre-charge resistor and its job of keeping the 
> contactor
> output at pack voltage.
>
> Bottom-line, I had caused two issues. First, the DC Converter was
> continually draining off charge from the pre-charge resistor, so my 
> battery
> pack was being drained when I wasn't expecting it and stressing my
> pre-charge resistor with constant current flow. Second, the pre-charge
> resistor wasn't getting to do its job of keeping the controller caps 
> charged
> up so I wouldn't have a high current inrush when the contactor was
> activated.
>
> I now have a solid-state relay on order to have a separate enable switch 
> for
> the DC-DC converter off the key switch (without a pre-charge resistor!).
> Until then, I have the manual disconnect off whenever I'm not driving the
> car. No sense draining the pack and continuously switching the converter 
> on
> and off needlessly.
>
> Reading through Mike Brown's "Convert It" book, he clearly goes over this.
> I obviously missed that fine detail the first time!
>
> I will obviously do the same thing for the new heater I'm getting ready to
> install.
>
> I know that many people have two contactors between the battery and the
> motor controller. So far, I only have the one. I know that I'm missing 
> an
> element that could be a key safety factor if the main contactor welds
> closed. I'm trying to figure out where I would put the second one. They
> are big!
>
> I hope this helps some other person with less experience avoid this 
> mistake.
>
> Mike
>
>
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## EVDL List (Jul 27, 2007)

>> I now have a solid-state relay on order to have a separate enable switch
>> for the DC-DC converter off the key switch (with no precharge resistor)...



> matt lacey wrote:
> > Make sure the solid state relay output is DC rated.
> > The AC rated ones are just an SCR, which means you can turn it on no
> > problems, but can only turn it off when there is no current flowing.
> ...


----------



## EVDL List (Jul 27, 2007)

Mike,

Interesting timing on your message. Thanks for confirming what I've
suspected for a while. I've been struggling lately to figure out why my
range is reduced on Mondays. I don't use my EV as consistently on the
weekends. It may sit totally unused or be used for a short trip late in the
day on either Sat or Sun. Turns out my DC-DC (Iota DLS-55; yes I know it's
not the best) was wired by the guys who did my conversion so that the
positive input wire goes to the main contacter and the negative input wire
goes to the controller. I don't think I have a precharge resister - the
guys who did my conversion say on their website that Logisystems controllers
don't need them and I can't see one (Yes I know that may be an issue in
itself).

Anyway looking at the Iota manual (very short and pretty vague in spots) it
looks like it tries to float my accessory battery at 13.6V. If that's true
then it will be continually drawing from my traction pack to keep it
there. And if I don't happen to be charging at the time, that means my pack
will be drawn down. That might explain my reduction in range on Mondays.

I have a main circuit breaker and I've started activating it to open the
traction pack circuit whenever my car is parked and not charging (maybe
that's what you meant by your "manual dissconnect"). Anyway, that should
prevent the DC-DC from needlessly sucking power from the traction pack.
And, as you say Mike, it should also prevent the converter from going on and
off all the time which saves wear and tear on it too.

btw - when my Quick Charge charger is finished its AGM routine, it switches
to float so it's drawing AC power until I unplug it; that should mean I
don't have to worry too much about the DC-DC unnecessary drawing down the
traction pack during my overnight charge.

Anyway - good catch Mike!


Peter Flipsen Jr
Meridian, ID
http://www.evalbum.com/1974



> Mike Nickerson <[email protected]>wrote:
> 
> > Hello everybody,
> >
> ...


----------



## EVDL List (Jul 27, 2007)

Lee,

It's good to know about the energy use on float, but two points:

1. I don't let it float that long. Whether I'm using my EV that day or not
I unplug the charger in the morning. Thus it might float the traction pack
for 8-10 hrs at the most (more often 5-6 hrs) What I've added now is that
when I do unplug it, I also engage the main breaker to prevent the float
from the DC-DC to the accessory battery from drawing off my traction pack.

2. As I think about this issue I've been struggling also with how best to
keep my accessory battery charged. If I re-wire the DC-DC so it only comes
on when the key is on (and I don't know how to do that), wouldn't that also
mean that it doesn't come on when the charger is on? Short of using a
separate charger and eliminating the DC-DC altogether, isn't that precisely
the best time to charge the accessory battery (via the DC-DC)? btw - I only
have a single 20A circuit in my garage.


On a related note, I've been thinking about another option for the weekends
and that's to install one of those battery shutoff switches on the accessory
battery. Any thoughts on that?

- Peter



> > btw - when my Quick Charge charger is finished its AGM routine, it
> switches
> > to float so it's drawing AC power until I unplug it; that should mean I
> > don't have to worry too much about the DC-DC unnecessary drawing down the
> > traction pack during my overnight charge.
>
> Recognize that most chargers have very low efficiency with light loads.
> You could easily consume more electricity with your charger on 24hrs
> float than with 1 hour of charging. Many EV batteries don't benefit from
> float, either.
>
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## EVDL List (Jul 27, 2007)

Thanks everyone for the interesting discussion. I hadn't thought about the
DC-DC converter having capacitors too. I just ordered inrush limiters to
install when I do my rewiring. I'm assuming my MES-DEA RM4 heater wouldn't
need that. I should think it wouldn't because it should present a resistive
load. I hope not because it could draw 30 amps on startup and I couldn't
find current limiters that could support that kind of draw. 

I did get DC rated solid-state relays. They are rated for 220V DC and 40A
load when used with a heatsink. I got 5 ohm, 12A limiters. I'm thinking of
using two in series to keep the inrush down to 14A or so. I hadn't ever
stopped to think that they are really just high-current thermistors with
negative coefficients, but that makes sense.

I have strong feelings about the DC-DC converter. My car arrived without
one and I spent the first few weeks driving without it. It was my first
purchase and upgrade. I learned two things:

1. It is really nerve-wracking to realize that you can only drive so long
after dark and the car will die when the 12V battery dies. (I learned that
the hard way!)
2. Most vehicle accessories claim to run on 12V, but what they really
like is to run on the 13-14V from the alternator. With only a 12V battery,
headlights are dim, windshield washers move slowly, etc.

I really think it's important to have the converter active while you're
driving, just in case. Once you've done that, there is really no reason to
have it run with the key off, as long as you have a battery you trust. The
battery only has to provide enough juice to turn on the relay that enables
the DC-DC converter. After that's done, the battery is being charged again.
As long as everything is working as designed, your accessory battery should
be fully charged when you park the car.

I'm going to hook my DC-DC converter up to the hot (always on) side of the
main contactor. It will then go through the DC relay, through the inrush
limiter and into the positive side of the DC-DC converter.

Mike

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of SLPinfo.org
Sent: Thursday, September 23, 2010 2:13 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Caution When Installing HV Accessories

Lee,

It's good to know about the energy use on float, but two points:

1. I don't let it float that long. Whether I'm using my EV that day or not
I unplug the charger in the morning. Thus it might float the traction pack
for 8-10 hrs at the most (more often 5-6 hrs) What I've added now is that
when I do unplug it, I also engage the main breaker to prevent the float
from the DC-DC to the accessory battery from drawing off my traction pack.

2. As I think about this issue I've been struggling also with how best to
keep my accessory battery charged. If I re-wire the DC-DC so it only comes
on when the key is on (and I don't know how to do that), wouldn't that also
mean that it doesn't come on when the charger is on? Short of using a
separate charger and eliminating the DC-DC altogether, isn't that precisely
the best time to charge the accessory battery (via the DC-DC)? btw - I only
have a single 20A circuit in my garage.


On a related note, I've been thinking about another option for the weekends
and that's to install one of those battery shutoff switches on the accessory
battery. Any thoughts on that?

- Peter



> > btw - when my Quick Charge charger is finished its AGM routine, it
> switches
> > to float so it's drawing AC power until I unplug it; that should 
> > mean I don't have to worry too much about the DC-DC unnecessary 
> > drawing down the traction pack during my overnight charge.
>
> Recognize that most chargers have very low efficiency with light loads.
> You could easily consume more electricity with your charger on 24hrs 
> float than with 1 hour of charging. Many EV batteries don't benefit 
> from float, either.
>
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## EVDL List (Jul 27, 2007)

My,my how complicated it can be, I am so glad I use Wayne's (of electric
Blue) method and use the glider's alternator to keep the 12 V. topped off
with the internal Alternator regulator's control. 1/2 a mile down the road
and the battery (12.8v.) is fully charged and no power from the pack when
stopped.
Regards,
Dennis Lee Miles (Director) E.V.T.I. inc.
www.E-V-T-I-Inc.COM (Adviser) EVTI-EVA Education Chapter
Phone (863) 944 - 9913
---------------------------------------------------------------------------=
-------------------------------------------------


> SLPinfo.org <[email protected]> wrote:
> 
> > Lee,
> >
> ...


----------



## EVDL List (Jul 27, 2007)

> Mike Nickerson wrote:
> > I'm assuming my MES-DEA RM4 heater wouldn't need that. I should think it
> > wouldn't because it should present a resistive load.
> 
> ...


----------



## EVDL List (Jul 27, 2007)

Lee,

I can't think of anything. My car has manual door locks and windows, and no
security system (Hardly necessary anyway. A thief would have to be pretty
desparate to want to steal a 1991 Plymouth Colt). For a clock I use a
battery operated unit velcroed to the dash. I almost never use the radio -
with my short 5 mile rush hour commute I have lots of stop and go and pass
two schools and find the radio is just a distraction. So I would not lose
anything by shutting off the accessory battery.
- Peter Flipsen Jr
Meridian, ID
http://www.evalbum.com/1974

>
> > another option... install one of those battery shutoff switches
> > on the accessory battery. Any thoughts on that?
>
> Do you have any 12v loads that must be powered all the time? Things like
> clocks, radio presets, trip odometers, security systems, remote locks,
> etc. will lose their data if you don't keep the 12v power on.
>
> --
> Lee A. Hart | Ring the bells that still can ring
> 814 8th Ave N | Forget the perfect offering
> Sartell MN 56377 | There is a crack in everything
> leeahart earthlink.net | That's how the light gets in -- Leonard Cohen
>
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## EVDL List (Jul 27, 2007)

> A DC/DC converter can imitate this solution (fixed 14.x volts when the key
is on, off when the key is off). Or, you can get a little fancier:

> 1. You can wire the DC/DC to be on all the time, and float the battery
> at 13.x volts. (I don't happen to like this solution; see above).

> 2. Your Iota can run on AC or DC. You can switch it to run on AC when
> plugged in and charging the main pack, and on DC when driving.
> If you do this, you'll want the Iota to have the "IQ" module so it
> switches to "float" upon reaching full charge or it will chronically
> overcharge the 12v battery.

> 3. You could add a separate small 12v battery charger (battery
> maintainer) that only operates when AC is connected and the main
> pack is being charged.

Remember that this limits the total draw you can have while driving.
Probably not a big deal until winter when your entire commute distance might
be in the dark. Also, I found that headlights are dimmer than I would
normally expect on a 12V battery (instead of 13.xV converter/alternator).
Since my commute time is 30-40 minutes, I think I might risk draining the
battery.

I was actually doing this until the cheap battery charger failed (without
any indication) and left me stranded because the 12V battery died.

Personally, I've gone with the compromise of the DC-DC converter on while
the key is on. It can still overcharge the battery, but the system works
most like the other cars I drive.


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## EVDL List (Jul 27, 2007)

>> 3. You could add a separate small 12v battery charger (battery
>> maintainer) that only operates when AC is connected and the
>> main pack is being charged.



> Mike Nickerson wrote:
> > Remember that this limits the total draw you can have while driving.
> > Probably not a big deal until winter when your entire commute distance might
> > be in the dark. Also, I found that headlights are dimmer than I would
> ...


----------



## EVDL List (Jul 27, 2007)

Lee and Mike 

Thanks for the input. I literally just finished removing the Iota. Decided to try without it. will charge the accessory battery with my 12v smart charger while I charge the pack. My pack charger draws no more than about 10 amps and I can run the other one at 2 amps and it shouldn't overload my single garage circuit. 

thanks for the heads up on the wiring, Mike. May need to do that at some point. Am also considering xenon headlights and LEDs elsewhere to reduce the current load. May even go into the archive and look at the discussion on more efficient wiper motors that I recall from some time back. But we just moved to a new house and my wife's been out of work for quite a while so cash is short as you might imagine. So those things may need to wait some.

Peter Flipsen Jr 

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