# the missing 35 volts puzzle



## Elanimal28 (Nov 18, 2013)

I’m missing 35 volts. My battery voltage is 98v fully charged and when I applied it thru the 750 ohms 25 watt resistor, it took almost 24 seconds to reach 90v at the controller( *Curtis 1231C* 96-144VDC 500A). Then I let the battery drain for a couple of days and tried to pre-charge the controller. Now the battery reads 91v, but the voltage after the pre-charge resistor only goes up to 56v and it stops there. Where did the 35v go?
 I will note that the resistor gets warm to the touch and I wasn’t happy with a 20 sec wait time for pre-charging.
Could my resistor be defective?
I’m thinking of trying a 500 ohm 25 watt resistor to solve the missing 35 volts puzzle and to cut down my pre-charge time by 33 % (compared to the 750 ohm)
Here’s my math: 98v / 500 ohm= 0.196 amps . 
0.196 x 98 = 19.208 watts 
Ideas, comments and suggestion?


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## major (Apr 4, 2008)

> Here’s my math: 98v / 500 ohm= 0.196 amps .
> 0.196 x 98 = 19.208 watts


You do realize that you math relates to the instantaneous values when you first connect the resistor?

I think you can benefit from a better understanding of pre-charge. This is a good paper: http://liionbms.com/php/precharge.php


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## Elanimal28 (Nov 18, 2013)

major said:


> You do realize that you math relates to the instantaneous values when you first connect the resistor?
> 
> I think you can benefit from a better understanding of pre-charge. This is a good paper: http://liionbms.com/php/precharge.php


Thanks for the link. It was very informative, but I still can’t figure out why the pre-charge voltage stops charging the capacitor at 56v if my battery voltage is 91v and if its 96-98v the pre-charge voltage to the capacitor goes up to what I think is normal voltage ( 90v or 94v).


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## major (Apr 4, 2008)

It is obvious that the precharge resistor has the 35 Volt drop across it and that means that there is 46 mA flowing. I don't understand your concern. You don't need or even want to charge to 100%. Precharge eliminates the initial arc and get the voltage somewhat close then close the main contactor and forgetaboutit.

Why is your battery only at 91V where it was at 98V fully charged


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## Elanimal28 (Nov 18, 2013)

I thought I was supposed to precharge to 80% of the battery voltage.
I was worry about the 35v difference being too high of a volatge difference for the contactor.
Oh and the voltage dropped down to 91 because my dc-dc stays on all the time.


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## major (Apr 4, 2008)

Elanimal28 said:


> I thought I was supposed to precharge to 80% of the battery voltage.
> I was worry about the 35v difference being too high of a volatge difference for the contactor.
> Oh and the voltage dropped down to 91 because my dc-dc stays on all the time.


So you worry about a few percent on the precharge and not that you're killing your battery with DC/DC drain 

I don't know about the specifics on that controller and precharge resistor. Ask your dealer. It isn't something which would bother me. Generally speaking, guys use way to high an Ohmic value resistor. And beats me why you even attempt to precharge with a low battery like that. What is the low voltage cutout for your controller? What is the normal standby current draw for your controller?


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## Elanimal28 (Nov 18, 2013)

major said:


> So you worry about a few percent on the precharge and not that you're killing your battery with DC/DC drain
> 
> I don't know about the specifics on that controller and precharge resistor. Ask your dealer. It isn't something which would bother me. Generally speaking, guys use way to high an Ohmic value resistor. And beats me why you even attempt to precharge with a low battery like that. What is the low voltage cutout for your controller? What is the normal standby current draw for your controller?


I am in the testing phase and so for now I have left the dc-dc on because it's built in to the charger delta-q 1kw. I would have to pre-charge the battery charger as well if I connect/disconnect it because it has two big capacitors as well. 
The controller's recommended resistor by the manufacture is 750 ohm 25 watt
The cutoff voltage is 64v. and the normal standby current is less than 20 mA


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## major (Apr 4, 2008)

drai


Elanimal28 said:


> I am in the testing phase and so I for now I have left the dc-dc on because it's built in to the charger delta-q 1kw. I would have to pre-charge the battery charger as well if I connect/disconnect it because it has to big capacitors as well.
> The controller's recommended resistor by the manufacture is 750 ohm 25 watt
> The cutoff voltage is 64v. and the normal standby current is less than 20 mA


Then why isn't the recommended working for you? Have you inquired of the dealer from whom you bought the controller? If it isn't precharging to the low voltage cutoff for the controller, then the controller will not start, will it?* Why does it draw 46mA when normal is less than 20mA?

How long before you kill your battery by leaving your equipment drain it?

edit * I'll answer that question. Yes, it will start when you energize the main contactor.


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## Elanimal28 (Nov 18, 2013)

major said:


> drai
> 
> Then why isn't the recommended working for you? Have you inquired of the dealer from whom you bought the controller? If it isn't precharging to the low voltage cutoff for the controller, then the controller will not start, will it?* Why does it draw 46mA when normal is less than 20mA?
> 
> ...


I keep an eye on the batteries every day, but I have an extra Albright relay that I'm planning on using to connect and disconnect the charger/dc-dc converter.

I purchased the controller used and my "dealer" said it was working fine. If the battery pack's voltage is 96v or better, the capacitors charge up to 90v. I trying to figure out if the 35v drop occurs because the controller/ capacitors are not able to draw more than 56v across the resistor because the battery has only 91v instead of the 96-144v that the controller is design for? 

I don't know why it is drawing 45ma. How did you calculate the draw to be 45ma?


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## major (Apr 4, 2008)

Elanimal28 said:


> I keep an eye on the batteries every day, but I have an extra Albright relay that I'm planning on using to connect and disconnect the charger/dc-dc converter.
> 
> I purchased the controller used and my "dealer" said it was working fine. If the battery pack's voltage is 96v or better, the capacitors charge up to 90v. I trying to figure out if the 35v drop occurs because the controller/ capacitors are not able to draw more than 56v across the resistor because the battery has only 91v instead of the 96-144v that the controller is design for?
> 
> I don't know why it is drawing 45ma. How did you calculate the draw to be 45ma?


Circuit voltage always adds up to zero and Ohm's Law always applies. So you have a 91V battery and 56V at the controller, 35V must be across the resistor. You said the resistor was 750Ω. The only way the resistor can drop 35V is to have 46mA current through it.

Are you damaging your battery to have it at 91V? Like I was saying, that concerns me more than the stupid precharge. So it was an used controller you bought. Maybe it does not conform to spec any more and has a higher idle current drain. Also like I said, most guys use to large precharge resistors. I like to go low Ohmic and fast. Like 50Ω.


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## frodus (Apr 12, 2008)

Don't connect and disconnect the charger. It's meant to stay connected. There's really no reason to disconnect with an Albright contactor. 

Enable and disable the dc-dc like I told you.... Several times now.


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## Elanimal28 (Nov 18, 2013)

major said:


> Circuit voltage always adds up to zero and Ohm's Law always applies. So you have a 91V battery and 56V at the controller, 35V must be across the resistor. You said the resistor was 750Ω. The only way the resistor can drop 35V is to have 46mA current through it.
> 
> Are you damaging your battery to have it at 91V? Like I was saying, that concerns me more than the stupid precharge. So it was an used controller you bought. Maybe it does not conform to spec any more and has a higher idle current drain. Also like I said, most guys use to large precharge resistors. I like to go low Ohmic and fast. Like 50Ω.


This is what I figured out; you where correct about the controller drawing 45ma. At some point last week I decided to wire the controller KSI directly to the main contactor post without using a separate relay or switch as illustrated in the Curtis wiring schematic. See the picture bellow. When I disconnected the KSI, the controller charged up to the same battery voltage.
Thanks for helping me troubleshoot this (self-created ) problem. I was focused on the resistor being the problem, but when you suggested that the controller was drawing the 45ma, I took a look at the wiring diagram and figured it out.


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## Elanimal28 (Nov 18, 2013)

frodus said:


> Don't connect and disconnect the charger. It's meant to stay connected. There's really no reason to disconnect with an Albright contactor.
> 
> Enable and disable the dc-dc like I told you.... Several times now.


I was going to contact you after I figured out this problem because this is what I have notice. The charger is still connected like you told me, but in 3 days it drains the batteries down to 91v from 98v. The only thing connected to the battery pack is the charger. The batteries are not losing the charge on their own because they kept the same voltage for 2 months while I was building the back end of my vehicle where they were going to be installed. The drain from the charger can’t be minimal if it drains the battery down that much. 



frodus said:


> 1) The spark is fine, and it can and will happen. Its just charging the CAPS. If you want, you can "precharge" using a resistor similar to what you'd use for a controller to precharge the caps before connecting. .


I was thinking of pre-charging because you said it was ok. I know it's adding more complication to my set up but if I don’t have another choice.

What do you think I should do?


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## frodus (Apr 12, 2008)

Elanimal28 said:


> I was going to contact you after I figured out this problem because this is what I have notice. The charger is still connected like you told me, but in 3 days it drains the batteries down to 91v from 98v. The only thing connected to the battery pack is the charger. The batteries are not losing the charge on their own because they kept the same voltage for 2 months while I was building the back end of my vehicle where they were going to be installed. The drain from the charger can’t be minimal if it drains the battery down that much.


You need to disconnect everything on the ALWAYS ON of the DC-DC, so there's nothing draining the battery! Wire accessories or non-essential items to the SWITCHED OUTPUT like I outlined to you several times. If you have anything connected to the DC-DC, you are indirectly draining the battery through the DC-DC. Put all loads that don't require constant power on the SWITCHED OUTPUT, and enable/disable as I have previously outlined.



Elanimal28 said:


> I was thinking of pre-charging because you said it was ok. I know it's adding more complication to my set up but if I don’t have another choice.
> 
> What do you think I should do?


Don't precharge. You only do that the first time you connect to the batteries, and its only because you don't want the spark. The chargers are built to handle this.

Do what I have told you. This will be the last time I explain this, as I can't help it if you do not want to listen or implement.
http://www.diyelectriccar.com/forums/showpost.php?p=476513&postcount=6


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## Elanimal28 (Nov 18, 2013)

There is nothing connected to the charger. I don't have any accessories to connect as my project is not completed. The only things wired are the battery, controller and charger and one relay for precharing.

I have done as you said but, you think is OK that the charger is discharging the batteries with nothing plugged in on the dc-dc side?


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## frodus (Apr 12, 2008)

Draw out how everything is wired. It should not drain much at all unless it was damaged somehow. The wattage draw is very low with no load attached. 

Do you even know if it is actually draining the pack? Have you measured any current coming out of the pack going into the Charger? How do you know its the charger and not the batteries settling a little?


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## Elanimal28 (Nov 18, 2013)

frodus said:


> Draw out how everything isit,,,,ired. It should not drain much at all unless it was damaged somehow. The wattage draw is very low with no load attached.
> 
> Do you even know if it is actually draining the pack? Have you measured any current coming out of the pack going into the Charger? How do you know its the charger and not the batteries settling a little?


Everything is wired according to the schematic above. The charger is connected to the batteries and that's it. The relays are not connect permanently to the dc out put because I haven't received the Anderson connectors yet. So the only thing permanently connected to the batteries is the charger. There for i concluded that the charger is draining the batteries. I don't have any measuring device other than a 500 amp analog gauge but I don't think it will register a small load, so I haven't connected it.
As for the batteries settlings, they are used from a Chevy volt. I think they are settle already
Also when they sat for 2 months with nothing connected they held the same voltage 96.01
And when I disconnected the charger , they kept the same voltage while the charger was disconnected ( about 4 days).

The specifications for the charger doesn't say what the load is for the dc-dc. So when you say the wattage draw is minimal, how much are we talking about? And isn't a draw on the batteries however minimally going to kill them if the car is left unattended?


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