# BMS Supplying When Car Plugin and Run (Ignition On)



## mizlplix (May 1, 2011)

I use a DC/DC converter like in your option #2. It charges the aux battery during charging or while driving both.

I get about 53 miles if the DC/DC converter only runs during charging.

I get 48 miles or so if the DC/DC runs while driving too.

(I have a relay to isolate it from pack and aux batteries when I want to turn it off to prevent any parasitic drains).

Miz


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## iruraz (Sep 4, 2012)

@mizlplix thanks for your response. If I use option2 aux battery charges from main battery. And car's 12V system uses aux. batt. when the car is parked. Under this conditions does battery charging time increase? Or Does this condition bring new problems about bms or battery?

What do you think about option1? It seems reliable.

Regards.


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## mizlplix (May 1, 2011)

If I have a battery charging time increase, it is not really measurable to me. I am sure it is some.

With option 1, you will still need a 12VDC system for car systems and controls. Running it off of a DC/DC converter leaves you nothing as a back up if the converter fails while out on the road. You will be stranded. An aux. 12VDC battery is cheap insurance and redundancy to assure you can get home.

Use a battery, DC/DC converter (Instead of a power supply) and a small, onboard, 12VDC SLA battery. 

My opinion. It works for me.

Miz


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## Siwastaja (Aug 1, 2012)

Using a battery in the 12V system also allows you to size the DC/DC based on the average consumption of the 12V devices. Without a battery, you need to consider the peak power (lights when turning and braking at the same time and vacuum pump running, etc.)


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## iruraz (Sep 4, 2012)

> With option 1, you will still need a 12VDC system for car systems and controls. Running it off of a DC/DC converter leaves you nothing as a back up if the converter fails while out on the road. You will be stranded. An aux. 12VDC battery is cheap insurance and redundancy to assure you can get home.





> Using a battery in the 12V system also allows you to size the DC/DC based on the average consumption of the 12V devices. Without a battery, you need to consider the peak power (lights when turning and braking at the same time and vacuum pump running, etc.)



Option1 and option2 only plugin conditions. If we consider working conditions you are right about aux. battery. And what do you recommend about its connection? Is connection (below) right? I thought that aux. battery supplies 12V system everytime and when the main contactor is on main battery charges aux. battery through dc-cd converter and converter supplies 12V system continue working. Is dc-dc converter enought to supply 12 system and to charge lead-acid battery?

Thanks again.

Regards.


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## frodus (Apr 12, 2008)

Here's a couple different links that might help.

This explains a few different situations:
http://liionbms.com/php/wp_ignition_conundrum.php

Here's how Orion interfaces, they use a 100-240VAC power supply:
http://www.orionbms.com/charger-integration/interfacing-elcon/
http://www.orionbms.com/charger-integration/manzanita-micro/

Here's how Elithion interfaces, they use a 100-240VAC 12V charger and an aux battery:
http://lithiumate.elithion.com/php/brusa.php
http://lithiumate.elithion.com/php/zivan.php
http://lithiumate.elithion.com/php/elcon.php


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## TEV (Nov 25, 2011)

Basically you have to decide on a BMS first.


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## iruraz (Sep 4, 2012)

@frodus thanks for links. 

http://lithiumate.elithion.com/php/elcon.php

in the link above they refer to use supercap as a solution. But If we consider case of dc-dc converter failure we need to aux. battery for 12V accessories. How do we overcome this problem? 

@TEV we decided to use Orion BMS. with Elcon charger.

Regards.


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## frodus (Apr 12, 2008)

Use an aux battery if you want redundancy. If a DC-DC fails, a DC-DC only or DC-DC + Supercap solution will fail and kill the 12V system. If you want it to work ALWAYS, use a DC-DC + battery solution.


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## iruraz (Sep 4, 2012)

frodus said:


> Use an aux battery if you want redundancy. If a DC-DC fails, a DC-DC only or DC-DC + Supercap solution will fail and kill the 12V system. If you want it to work ALWAYS, use a DC-DC + battery solution.


@frodus I think I should use DC-DC + aux. battery. But I have some doubts about aux. battery connection. Have you any idea about DC-DC + aux. battery connection (or wiring)? Thanks.


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## frodus (Apr 12, 2008)

Connect the input of the DC-DC to your traction pack (with fuse on positive), the output of the DC-DC goes to the battery terminals (fuse the positive output of the DC-DC). Also connect the 12V system to the battery. Pretty much like the liionbms.com illustrations I posted.


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## iruraz (Sep 4, 2012)

frodus said:


> Connect the input of the DC-DC to your traction pack (with fuse on positive), the output of the DC-DC goes to the battery terminals (fuse the positive output of the DC-DC). Also connect the 12V system to the battery. Pretty much like the liionbms.com illustrations I posted.


I think you mean that connection below?




Another question : Is dc-dc converter sufficient to supply lead-acid battery or should I use charger for lead-acid battery and 12V system?


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## frodus (Apr 12, 2008)

Can you post the image, it's blocked for me.

Whether the DC-DC is sufficient to supply the LA battery + load, depends on the DC-DC.

The DC-DC IS the charger in this situation, it charges off the main pack.... so you only have to charge the main pack.


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## frodus (Apr 12, 2008)

Regarding the image below, that's exactly what I was thinking.

The "12V charger" here, is a DC-DC converter that is set for the charge voltage of a Lead acid battery. Something like 13.8V or so is what I normally see.

It needs to disconnect from the traction pack if voltage of the pack goes too low, or you need to disconnect if you leave it for long, as the DC-DC will discharge the pack over long periods.


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## iruraz (Sep 4, 2012)

@frodus thanks for your answer. In this case 12V system is supplied over lead-acid batt. or dc charger when ignition on? I mean does lead-acid supplies the 12V system and traction pack charges the lead-acid through dc charger?



frodus said:


> It needs to disconnect from the traction pack if voltage of the pack goes too low, or you need to disconnect if you leave it for long, as the DC-DC will discharge the pack over long periods.


I take notice of your warnings. 

Regards.


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## frodus (Apr 12, 2008)

Both the 12V battery and DC-DC converter supply power to the 12V system when ignition is on. Connect as above and you'll be fine.


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## iruraz (Sep 4, 2012)

@frodus thanks for your help. After completing high voltage and 12V system schematic, I want to ask advice from you.

Regards.


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