# voltage sag



## dexion (Aug 22, 2009)

Need a bit more. What are the battery amps you are pulling (not the motor amps) and what is the internal resistance of the batteries? Keep in mind paper is theoretical and doesnt take into account lessening the life of the pack. You can do 15 but you may not want to because of the life shortening properties of going below 50% dod depending on the type of battery you are using.


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## TheSGC (Nov 15, 2007)

We need more information, the model/brand of the batteries, what you have for a charger, your pack capacity (Ah) and your AMP draw and also how old is the pack.


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## alvin (Jul 26, 2008)

The batteries are everstart 27dc-6 12 volt 115 ah.
The pack is 120 volt. Don't know resistance. The batteries have been cycled 5 or 6 times. I am using a bonn charger. After charging and resting
for 24 hrs each battery is at 13.12 volts The amp draw at that sag is 200.
Alvin


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## TheSGC (Nov 15, 2007)

alvin said:


> The batteries are everstart 27dc-6 12 volt 115 ah.
> The pack is 120 volt. Don't know resistance. The batteries have been cycled 5 or 6 times. I am using a bonn charger. After charging and resting
> for 24 hrs each battery is at 13.12 volts The amp draw at that sag is 200.
> Alvin


You are getting some serious sag and drawing too much AMPs for those batteries this soon. They need a good 20 or so cycles of low AMP draw to properly break in. I have a set of Everstart MAXX29 125Ah and I keep them below 85 AMPs for cruising and try to stay under 180 AMPs for accelerating. My sag when I draw 200 AMPs is 92 volts without breaking in my batteries yet. My last set would only sag down to 95 volts when drawing 200 AMPs after braking in the batteries with 40 cycles.


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## alvin (Jul 26, 2008)

Thanks for your response. I have been keeping it under 100 amps most of the time. That's with very little pedal. It may not have been all the way 
down to 90 volts just glancing down athe meter. I'll make sure I keep it down till I get more cycles. What's all the jamesbattery posts.
Thanks 
Alvin


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## chansen (Mar 13, 2009)

I have a 120V FLA nominal system. Ten Trojan 1275 batteries. 120Ahr. I charge them to about 142V. I'm at about 100 cycles. Russco charger. Its a slow charger but that is good for batteries and it can charge them overnight so i fine with that.

After a full charge they float at 132V. After ten miles they float around 125V and sag to 120V with 100AMP load. After 25 miles they float at 120V and sag to 110V at 100AMP load.

At 30 miles I try to be home because they are closing in on 80% discharge and I have a long hill to my house


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## alvin (Jul 26, 2008)

Thanks for telling me how yours sags. I really did not know what might be normal. Yesterday I made the effort to not get above 100 amps.
I drove to the closest town , for the first time , about 12 miles round trip.
I would barely press the pedal and kept it about 50 to 75 amps. Then I drove another 4 or 5 miles. When I parked in the garage I was down to about 119 volts. Thats all the range I have. The truck weighs around
3300 lbs. 
Alvin


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## chansen (Mar 13, 2009)

You are getting lower range than I would expect for pack based upon a 115 Ahr battery. Even at 3000+ lbs. I dont have any experience with the Everstarts. You should be getting 25-30 miles/chrg especially when you are not drawing more than 100AMPS.

What is the final charge voltage on your pack? You may try to equalize the pack for a while. Is it cold where you live?

Try to feel around all of the connections you made (carefully) to feel for heat for a bad connection (the thinking here is that the sag is from a high resistance outside of the batteries themselves). I expect you used 2/0 or similiar cable?


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## alvin (Jul 26, 2008)

Hi. My voltage is about 131.xx. After a run I get out and feel for heat on everything. Every lug is cold except B- and M- but that is from the mosfets I guess. And they are just barely warm. My batteries have been
.01 to .02 volts after 24 hrs after charge. 2 /0 welding cable with hammer 
crimp lugs. I have had some acid mist shorting . maybe I am loosing something there. Temp high 60's. When I calculate range I use 400 watt per mile number.
About 15.5 miles.
Thanks
Alvin


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## alvin (Jul 26, 2008)

I found a lug that the cable was not tight in so I fixed that. I took it around the block , a little over 3 miles , the sag is a lot less. Now I am 
wondering about all the lugs. But the lugs never did get hot.


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## chansen (Mar 13, 2009)

With that voltage sag you are seeing, there is a lot of watts being dumped in the system, so you would have noticed if it all the watss were being lost in one place. So the poor lug theory sounds feasible since the heat would be distributed throughout the pack. I have screw terminals on my batteries and put the novalux compound on them and have very little measurable voltage loss over the terminals after 3 months of use.


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## hardym (Apr 2, 2008)

I have a great way to detect the resistance in the battery series connections... measure it while you are charging:

While putting about 10-20 A during the charging cycle, use a volt meter to measure the voltage between adjacent terminal posts. If you see more than 10mV, and 5mV per foot of 2/0 cable you probably have some resistance somewhere. Dig in and test each connection point. 

Easy ones to fix are betwen the lug and terminal post, fixed with cleaning and conductive grease.

Interestingly, Ive found that sometimes the 2/0 cable has resistance between the cable and the lug. This can be fixed by soldering the cable to the lug with a plummers blowtorch. If you dont fix this, it will heat up and melt your lugs. (believe me!!)


Mark

PS: I belive the gassing during FLA charging is highly corrosive, and causes resistance points in the cabling to form. Also causing corosison on battery compartment electrical items like throttle rheostats and fuse connectors.


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## dimitri (May 16, 2008)

hardym said:


> While putting about 10-20 A during the charging cycle, use a volt meter to measure the voltage between adjacent terminal posts. If you see more than 10mV, and 5mV per foot of 2/0 cable you probably have some resistance somewhere. Dig in and test each connection point.


Ditto, excellent advise!

I had one terminal noticeably warmer than others recently and there was voltage drop on that cell on Paktrakr display. After cleaning and tightening that connection the voltage drop disappeared and its not warming up any more than others.

I measured about 15mv drop during 20 amp charging on that connection, compared to 5mv or less on others.

I still can't explain how this happened over 3 months considering that connection was never loose, although probably not as tight as it should have been


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## alvin (Jul 26, 2008)

It is charging right now at 5 amps . The front 4 batts 13.34 to 13.36.
The back 6 are 13.31 to 13.39 . Over the week end I had cleaned every
connection and put CONTAX on them . Thats what I had. As far as torque
I don't know . I don't want to break them. I did want to solder them 
but was afraid I would melt the cover.
Thanks
Alvin


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## alvin (Jul 26, 2008)

I removed every cable on the vehicle and hammered the lugs down
tight. That fixed the sag. After a short test run I felt every lug for heat all
were cool except the neg. on the motor it was too hot to touch. The lugs 
I have are too large for my post. I made a copper washer for that one and that fixed it. Now on all of the neg. post on the batteries are too small for these lugs too. And when I tighten these down they feel like they may twist out of the battery. I'm thinking about using auto type battery clamps on the neg side. Anyone have an opinion on this? I would like to
hear it.
Thanks
Alvin


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## tj4fa (May 25, 2008)

Automotive style crimp on battery terminals like these below work great. 

Please note that the postive terminal battery posts are larger than the
negative so you would need both positive and negative terminal lugs to do it right.

This eBay seller sells both types and has free shipping.

http://cgi.ebay.com/ebaymotors/2-0-...1998994QQptZBoatQ5fPartsQ5fAccessoriesQ5fGear


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## alvin (Jul 26, 2008)

Thanks for link. They have lots of stuff there. Is there any reason
why autozone stuff would not work?


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## tj4fa (May 25, 2008)

Autozone stuff might work but the crimp-on style lugs would be better than the standard battery terminals with the bolt clamps.
Crimp-on lugs when done right will likely never corrode inside the crimp sockets and heat shrink over the cable/lug. Can't say that for the exposed wires under the clamp.

Plus when you look at Autozone or other hardware suppliers prices, you might reconsider.

I paid $3.69 for a small pkg of assorted heat shrink tube the other day and it amounted to only about 8" of usable heat shrink tube.

Convenience costs...


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## Guest (Nov 1, 2009)

alvin said:


> Thanks for link. They have lots of stuff there. Is there any reason
> why autozone stuff would not work?


Here is a good reason: Have a look!

http://greenev.sytes.net/electricvw/Electric_VW/The_Albums/Pages/Damaged_Brass_Connector.html 


Pete


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