# dc/dc wiring



## Hondacrzy (Mar 15, 2008)

PatricioIN said:


> Ok... my wiring diagram from KTA shows the output from the dc/dc going to a wiring strip (which I have) and then being used for various things. I'm sure that keeps everything all nice and tidy, but I don't actually have that much coming off my dc/dc... so...
> 
> I have kept the car's original battery for back up and extra power.
> 
> ...


I wired the Dc/Dc positive terminal to the main fuse block where the alternator originally connected to, that wa the wiring is protected by the original fuse. I also used a solid state relay to control the dc/dc, but it only charges at 13.5 volts. Foat voltage is 13.2v.


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## ElectriCar (Jun 15, 2008)

My Iota 55 is setup like a battery charger to not overcharge and maintain with a trickle after it charges up. It adjusts it's output like an alternator to keep the battery drain to a minimum.

I'd wire the plus directly to a fuse block or the plus terminal and have everything down stream fused. If you go backwards through a fuse it may not be sized properly for the DC unit's capability and you may not be able to draw as much current as it's rated as it would blow the fuse.


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## elevatorguy (Jul 26, 2007)

I was going to use my alternator wire to connect the dc/dc to the battery. It will work if your dc/dc puts out less current than the old alternator (likely) 
You may want to check the fuse and size it for your dc/dc for proper protection.


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## PatricioIN (Jun 13, 2008)

well.. my dc/dc is kinda wimpy at 25amps.. so I really don't think I'll have a problem with too much amperage. I'm sure the OEM alternator put out more than that.


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## tj4fa (May 25, 2008)

elevatorguy said:


> I was going to use my alternator wire to connect the dc/dc to the battery. It will work if your dc/dc puts out less current than the old alternator (likely)
> You may want to check the fuse and size it for your dc/dc for proper protection.


That's what I did. 

The Ranger's power distribution box had one of the alternator wires capable/fused for handling 60 amps. I de-rated the fuse down to 50 as the directions for my DC/DC converter called for.


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## judebert (Apr 16, 2008)

I did that too. DC/DC is wired directly to the battery with an appropriate fuse.


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## ElectriCar (Jun 15, 2008)

judebert said:


> I did that too. DC/DC is wired directly to the battery with an appropriate fuse.


Don't know about your situation but my IOTA 55 is rated for 190V max. While charging the system voltage is 175 for a 144V system.

*Obviously you don't want to over voltage your unit* so some recommend the DC unit only be powered when the ignition is on thus it will be OFF while the pack is on charge and experiencing this charging voltage.


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## judebert (Apr 16, 2008)

Since I'm running 120V, I don't have to worry about frying it from overvoltage. (Mine's a Todd, rated for up to 144V nominal.) 

However, I had the opposite problem last night: I was cruising along in the slow lane, and got surrounded by vehicles before my left-hand turn. I decided to trade a five-second voltage drop (I try to stay above 110V) for some acceleration to get in front.

As the voltage dropped below 96V, I smelled roasting insulation. I think my DC/DC converter was the culprit, pulling loads of amps to keep the lights and radio running. This implies that my accessory battery is shot. I'll have to check everything out when I get the time; meanwhile, I'm wondering if there's a way to disconnect the DC/DC converter when voltage drops.


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## dtbaker (Jan 5, 2008)

judebert said:


> ...I decided to trade a five-second voltage drop (I try to stay above 110V) for some acceleration to get in front.
> 
> As the voltage dropped below 96V, ... This implies that my accessory battery is shot.... if there's a way to disconnect the DC/DC converter when voltage drops.


I have a silly question.... not having a running EV yet, and not having watched pack voltage in action, I am wondering why pack voltage would drop so significantly under heavy load? 

I would expect motor amps to go up of course, but why would voltage suddenly go down?

D


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## ElectriCar (Jun 15, 2008)

judebert said:


> Since I'm running 120V, I don't have to worry about frying it from overvoltage. (Mine's a Todd, rated for up to 144V nominal.)
> 
> However, I had the opposite problem last night: I was cruising along in the slow lane, and got surrounded by vehicles before my left-hand turn. I decided to trade a five-second voltage drop (I try to stay above 110V) for some acceleration to get in front.
> 
> As the voltage dropped below 96V, I smelled roasting insulation. I think my DC/DC converter was the culprit, pulling loads of amps to keep the lights and radio running. This implies that my accessory battery is shot. I'll have to check everything out when I get the time; meanwhile, I'm wondering if there's a way to disconnect the DC/DC converter when voltage drops.


Don't know which unit you use but the IOTA 55 has brown-out protection to prevent just that! I just learned that yesterday. Hate it but I fear your device is toast now! Once you let that smoke out of it it's usually a goner. Sometimes though it will live to ride again, one more time maybe...

Good luck!


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## judebert (Apr 16, 2008)

dtbaker said:


> I have a silly question.... not having a running EV yet, and not having watched pack voltage in action, I am wondering why pack voltage would drop so significantly under heavy load?
> 
> I would expect motor amps to go up of course, but why would voltage suddenly go down?


It really depends on your batteries, but all lead-acids exhibit this behavior. It's called "sag". They have an internal resistance; the more you try to pull current out of them, the lower their voltage drops. It's just the way they work.

So much so that I actually watch the voltage while I drive to make sure I'm not accelerating too hard. My batteries shouldn't drop below 10.5V each, and they're not well balanced, so I try to keep my voltage above 110V total for the 10-battery pack.

Generally, AGM and gel batteries sag less than flooded batteries. (We also say they're "stiffer".) NiCd batteries hardly sag at all -- stiff as rocks. I don't know about lithium or NiMh, except that most people build lithium packs with such high voltage that they use (relatively) quite small current.

I was putting the pedal down; I was probably pulling my controller max current (supposedly 500A). The voltage sag is expected behavior.


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## dtbaker (Jan 5, 2008)

judebert said:


> It really depends on your batteries, but all lead-acids exhibit this behavior. It's called "sag".


aha! hence the need for accurate pack voltage in addition to 'fuel meter', unless components have internal protection....

so, do curtis controllers and curtis 1400 dc-dc convertors have built-in protectin of some kind? i.e. if they sense voltage sag, do they limit amps?

d


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## elevatorguy (Jul 26, 2007)

dtbaker said:


> aha! hence the need for accurate pack voltage in addition to 'fuel meter', unless components have internal protection....
> 
> so, do curtis controllers and curtis 1400 dc-dc convertors have built-in protectin of some kind? i.e. if they sense voltage sag, do they limit amps?
> 
> d


The 1400 specs claim operational range or 65 to 115% of nominal so it should be ok. The controllers will self limit at low voltage conditions, I think it is pretty low at 64 volts or so for the 1231C 144 volt version


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## dtbaker (Jan 5, 2008)

whew, ok, once again I am glad that KTA specced out components that are keeping me out of trouble.


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## PatricioIN (Jun 13, 2008)

update:...from what little driving I've done thus far, my dc/dc hooked directly to my 12v batt + term is working fine. 12v batt stays charged as it should and all power accessories work.. though some things like the power windows are SLOW... they work, just slow. Of course, my dc/dc is only 25amps. I wil probably replace it eventually with one capable of much more output.


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## tj4fa (May 25, 2008)

PatricioIN said:


> update:...from what little driving I've done thus far, my dc/dc hooked directly to my 12v batt + term is working fine. 12v batt stays charged as it should and all power accessories work.. though some things like the power windows are SLOW... they work, just slow. Of course, my dc/dc is only 25amps. I wil probably replace it eventually with one capable of much more output.


Hmmm...that explains why my windshield wipers are slower than normal. I didn't even think of the DC/DC converter output as the cause.


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## Jimdear2 (Oct 12, 2008)

tj4fa said:


> Hmmm...that explains why my windshield wipers are slower than normal. I didn't even think of the DC/DC converter output as the cause.


Something I have never seen mentioned when reading threads about DC-DC converters is the actual regulated output voltage of the converter(I may have just misses it). I'm an old car guy and I know that everything in the car is really designed to work at about 14 volts alternator output.

I'm assuming that the DC-DC converters are being set up to produce 14+- 0.5 volts output and are current regulated to prevent overcharging the auxillary battery. Am I correct? 

If they are set to 12.2 +-0.5 volts, everything will work slower and weaker.

I haven't asked this question or researched this before because I won't be using a converter in my setup. But now my curiosity is aroused.

Jim


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## tj4fa (May 25, 2008)

Jimdear2 said:


> I'm assuming that the DC-DC converters are being set up to produce 14+- 0.5 volts output and are current regulated to prevent overcharging the auxillary battery. Am I correct?
> 
> Jim


EVA said to adjust mine to 13.5V. I believe it's a 350W converter and figured the setting was to recharge the battery. 

If it seems too slow after driving in the next rain, I might tweak it up to 14V and see if that makes any difference.

In Florida, you're s'posed to have your headlights on when it's raining so that will be an additional drain.

Edit--->
Hmmm...this guy has the same DC/DC converter I do and had some issues with it in his S-10.

http://www.sparky-ev.com/EV/EV_DCDC.php


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## PatricioIN (Jun 13, 2008)

Jimdear2 said:


> Something I have never seen mentioned when reading threads about DC-DC converters is the actual regulated output voltage of the converter(I may have just misses it). I'm an old car guy and I know that everything in the car is really designed to work at about 14 volts alternator output.
> 
> I'm assuming that the DC-DC converters are being set up to produce 14+- 0.5 volts output and are current regulated to prevent overcharging the auxillary battery. Am I correct?
> 
> ...


mine is supposed to put out 13.7 volts.. haven't tested the output, but keep in mind that I've had the PS pump and heater working all the time too! When the heater/fan is turned off, the windows work at normal speed.


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