# new aux batt dead in 2 weeks :(



## Ziggythewiz (May 16, 2010)

You can stick an ammeter in there to see how much juice is being used, and track down all your phantom loads. Then minimize whatever you can, or identify essential systems that you wouldn't want turned off if the car is sitting for a while, and those can be powered separately from the switch.


----------



## frodus (Apr 12, 2008)

Sure, get a DC-DC converter, so your parasitic load draws off the main pack and won't kill the Aux battery.

Or go through the entire car and eliminate non-essential parasitic loads.

If you have a 50Ah battery, and draw 100mA, it'll last you roughly 20 days. Doesn't seem like a huge load, but when it's running 24-7, it adds up. 100mA will discharge the battery 2.4Ah a day.


----------



## dladd (Jun 1, 2011)

I was having this problem, the main source of the drain in my case appears to be the DC/DC converter itself, it slowly drains the 12v battery when it is not on. The solution I was given on the forums here was to install a relay on the 12v line between the DC/DC and the 12v battery so it's disconnected when not on. As a short term solution I went the other way and just wired my DC/DC to be always on. Problem solved. 

Not sure if your DC/DC is the same (mine is an older IOTA), but I too was having my new 12v battery die over a long weekend, when it really should last a few weeks.

Eventually (I seem to say that a lot...) I'd like to add the relay and rewire the DC/DC to be only on with ignition again, but it's been fine for many months being always on. It seems likely that it will cause earlier DC/DC death though, just since it's being used so much more (24/7 instead of 1hr/day).


----------



## skooler (Mar 26, 2011)

dladd said:


> I was having this problem, the main source of the drain in my case appears to be the DC/DC converter itself, it slowly drains the 12v battery when it is not on. The solution I was given on the forums here was to install a relay on the 12v line between the DC/DC and the 12v battery so it's disconnected when not on. As a short term solution I went the other way and just wired my DC/DC to be always on. Problem solved.
> 
> Not sure if your DC/DC is the same (mine is an older IOTA), but I too was having my new 12v battery die over a long weekend, when it really should last a few weeks.
> 
> Eventually (I seem to say that a lot...) I'd like to add the relay and rewire the DC/DC to be only on with ignition again, but it's been fine for many months being always on. It seems likely that it will cause earlier DC/DC death though, just since it's being used so much more (24/7 instead of 1hr/day).


I had exactly the same issue, almost killed 4 Sinopoly 60AH cells costing about $300-400. 

The solution was to leave it always on. I haven't had an issue with the main pack being drawn down and the 12v accessory battery sits at 14.3ish volts.

You could add a relay between the DCDC and aux but I dont really see the need - Unless ofcourse the parasitic load is not the DCDC converter.

I used a digital clamp meter for about £30 to find the parasitic load. I was really surprised when I saw the output on the DCDC changed to a negative number when I took away the input supply!!


----------



## skooler (Mar 26, 2011)

Forgot to add....

My chennic gets VERY hot under load.

It is a good idea to be always on so that the DCDC doesn't have to catch up with the aux battery when it is first powered up.

A not full aux battery is a (BIG) load for the DCDC converter. Mine gets close to 90 degrees C if I turn it off for several hours

I toyed with the idea of adding an Anderson connector on the input and output so that it can be disconnected for periods where the ca isn't being used.


----------



## socko (Sep 21, 2008)

Hey this is great stuff.. Never would have guessed the DC-DC would be a closet parasite. Shame shame. Must investigate further. 

Thanks much for the feedback!


----------



## onegreenev (May 18, 2012)

I used a DC DC. I am still going to use one but because I have a few extra cells and built a nice 4 cell 100Ah battery. This will be used with a Powerpack as a DC DC converter. I will have 15 volts output, 12 volt output and any other needed. I may even do a 24 because I have a couple smaller 24 volt contactor switches for small loads and to isolate HV from the 12 volt system.


----------



## dtbaker (Jan 5, 2008)

skooler said:


> The solution was to leave it always on. I haven't had an issue with the main pack being drawn down and the 12v accessory battery sits at 14.3ish volts.


agreed..... this way you avoid the big draw as the dc-dc recharges the aux battery, which has been drawing from if the dc-dc and aux are in parallel. 

You really need to either wire with dc-dc + aux in parallel 'always on' powered from main pack, OR use a relay or contactor to disconnect BOTH the main pack and aux battery when you key-off.


----------



## skooler (Mar 26, 2011)

dtbaker said:


> agreed..... this way you avoid the big draw as the dc-dc recharges the aux battery, which has been drawing from if the dc-dc and aux are in parallel.
> 
> You really need to either wire with dc-dc + aux in parallel 'always on' powered from main pack, OR use a relay or contactor to disconnect BOTH the main pack and aux battery when you key-off.


Makes sense either way, except the latter is likely to cause more problems and cost more... 

My advice is to just hard wire it in with the Anderson disconnects on the input and output. if you know the car will be stood for any significant period then disconnect the anderson connectors 

Cheers,

Mike


----------



## dougingraham (Jul 26, 2011)

socko said:


> Hey this is great stuff.. Never would have guessed the DC-DC would be a closet parasite. Shame shame. Must investigate further


Most likely there is a bleeder resistor across the output caps that causes the load.


----------



## dtbaker (Jan 5, 2008)

most of the dc-dc units pull a surprisingly high amount of juice even when just sitting.... Hence, I am a believer in wiring the dc-dc 'always on' powered from the main pack, in parallel with a small 12v aux. Also recommending disconnect of BOTH main pack and aux if vehicle is sitting more than a couple days.


----------

