Roadtrek RS Sprinter parasitic drain

gte

2008 RS
I know the subject of parasitic drain has been discussed a lot on the forum. In March I installed new AGM coach and engine batteries. I have not driven it much in the past several months but weekly I check them and I have a battery disconnect switch on the coach batteries. The voltages have remained constant at around 12.8 volts or so. This week I checked and the coach batteries were fine but the engine battery was so low it would not power the engine pre-heater on the diesel. I used my generator to charge the battery, got it started and connected shore power at home for 48 hours. I had the battery load tested and it is fine. When I put the RS back in storage I disconnected the coach batteries and this time I disconnected the engine battery using the disconnect near the accelerator pedal. I also checked the current with a DVM at the disconnect and found it to be 1.4 amps. I know there is a drain on the coach circuit even with the power switch in the coach off but had no idea there was a drain on the engine battery with nothing on at the dash. Is this normal or do I have a short someplace? My old engine battery sat for months at a time and never ran down. Sorry for the long post.
 

icarus

Well-known member
The isolator relay has a significant no load draw~1 amp iirc. Hence the advice to install a positive battery disconnect in the house batteries. I have also seen those cheap relays stick, forcing the vehicle battery to try to energize the house even when the house batteries are disconnectd. I suggest changing out the isolator with a BlueSea mag latch realty that draws no current at stand by.

Icarus
 

gte

2008 RS
The isolator relay has a significant no load draw~1 amp iirc. Hence the advice to install a positive battery disconnect in the house batteries. I have also seen those cheap relays stick, forcing the vehicle battery to try to energize the house even when the house batteries are disconnectd. I suggest changing out the isolator with a BlueSea mag latch realty that draws no current at stand by.

Icarus
Thanks Icarus
The parasitic draw on my coach batteries is about 1.7 amps. This is why I installed the battery disconnect switch. My switch has a removable screw so it is clearly disconnected. I may have installed it incorrectly since I put it on the negative terminal of the coach batteries. Should it be on the positive terminal?

The parasitic drain that surprised me is on the engine battery. This drain was measured after the coach batteries were disconnected.

I assume the isolator you recommend does not draw any or at least much lower current but would not help with the engine battery drain
 

icarus

Well-known member
Negative terminal is proper.

I would disconnect the bwttery isolator and check the current draw on the vehicle battery.

Icarus
 

gte

2008 RS
So I got about 1.4 amps on the engine battery with separator connected and the coach battery disconnected. Are you saying it might be different if I disconnect the separator? I should mention this is a brand new separator I installed a few months ago.

I will try your suggestion as it is an easy thing to do
 

icarus

Well-known member
If you are getting a 1.4 amp draw after you disconnect the relay, clearly something is wrong. The radio has a parasitic draw, and the ECU might as well. You could consider pulling each fuse one at a time and watch the ammeter and find what circuit has the draw, and then go from there.

Icarus
 

gte

2008 RS
No I got 1.4 amps with the separator connected. I will try disconnecting it and measure again.

The strange thing is I had the OEM engine battery for 8 years and never had this problem before. The OEM engine battery never ran down even after 2-3 months in storage with no solar or trickle carger in place.
 

gte

2008 RS
Thanks Icarus. I should have thought of that. I also looked at the Sure Power installation instructions and found the following paragraph:

Checking the Operation:
Start the vehicle or apply a charge to the
main battery. Once the main battery rises to 13.2V* the Battery Separator
should activate(CLICK ON). Turn off the
vehicle or remove the charge to the main battery. The Battery Separator
should disconnect(CLICK OFF) the auxiliary battery once the voltage on the main battery
drops below 12.8V*.

So I should be able to hear it click on and off if I do the above.

I read on one of the other sites something about checking with an ohmmeter to see if the two terminals are connected or not. There would be voltage on the terminals both with the engine off and running. I have never used a DVM ohmmeter on a live circuit so am not sure about this one.
 

gte

2008 RS
I was just wondering if the new separator had more current draw than the old one, perhaps.
The new separator is a Sure Power 1315-200 which is the same as the old one, but who knows.
According to the spec sheet the Quiescent Current is 13 mA and the Relay Drive Current is 1.5 Amps. If the relay is on when the engine is off then I assume it is drawing 1.5 amps. This is consistent with my current measurements at the coach battery of about 1.7 amps.
 

icarus

Well-known member
The new separator is a Sure Power 1315-200 which is the same as the old one, but who knows.
According to the spec sheet the Quiescent Current is 13 mA and the Relay Drive Current is 1.5 Amps. If the relay is on when the engine is off then I assume it is drawing 1.5 amps. This is consistent with my current measurements at the coach battery of about 1.7 amps.
That is why I have always suggested the Bluesea mag latch relays that draw no current on stand by. 1.7 amps for an idle device is crazy on a small battery system. That is 40 ah/day, or about 20% of the toilet battery capacity, or closer to 40% of the 50% suggested depth of discharge for a deep cycle battery!

Icarus
 

RT.SS

Active member
Hi Gary,
At 8 years old, your chassis battery probably is on its last leg and not holding charge as it’s used to be. I tested my Agile and it draws 0.8 amps with the engine off, but I have a Viper alarm that is constantly drawing power from the chassis battery.

Why not test the separator if it is properly functioning. With the engine off, disconnect the coach battery from the separator then check the voltage from the chassis battery separator post to ground, you should get 12 (+) volts and 0 volts to coach battery separator post to ground. To check if it activates, start the engine and wait a few minutes, then check both separator posts to ground for voltage, you should see a reading of 13 (+) volts on both posts...?

The separator is bi-directional, so you would also check if it activates and charges the chassis battery when on shore or generator power. Just reverse the process above by disconnecting the chassis battery to the separator instead.

I have replaced my separator with the Blue Sea ML-ACR after my solar panel installation. The Sure Power separator does activate during solar charging and eats about 1.5 amps of my solar harvest, that’s huge. I like the Blue Sea as it draws very low current (<40mA to monitor terminal voltage) in the ON or OFF states, and draws moderate current for very short time when changing state. I can also manually turn it ON or OFF from a remote switch in the dashboard. You can check the installation pictures here: http://roadtreklife.blogspot.com/2015/12/battery-isolator-upgrade-to-blue-sea-ml.html
 

gte

2008 RS
Hi Gary,
At 8 years old, your chassis battery probably is on its last leg and not holding charge as it’s used to be. I tested my Agile and it draws 0.8 amps with the engine off, but I have a Viper alarm that is constantly drawing power from the chassis battery.

Why not test the separator if it is properly functioning. With the engine off, disconnect the coach battery from the separator then check the voltage from the chassis battery separator post to ground, you should get 12 (+) volts and 0 volts to coach battery separator post to ground. To check if it activates, start the engine and wait a few minutes, then check both separator posts to ground for voltage, you should see a reading of 13 (+) volts on both posts...?

The separator is bi-directional, so you would also check if it activates and charges the chassis battery when on shore or generator power. Just reverse the process above by disconnecting the chassis battery to the separator instead.

I have replaced my separator with the Blue Sea ML-ACR after my solar panel installation. The Sure Power separator does activate during solar charging and eats about 1.5 amps of my solar harvest, that’s huge. I like the Blue Sea as it draws very low current (<40mA to monitor terminal voltage) in the ON or OFF states, and draws moderate current for very short time when changing state. I can also manually turn it ON or OFF from a remote switch in the dashboard. You can check the installation pictures here: http://roadtreklife.blogspot.com/2015/12/battery-isolator-upgrade-to-blue-sea-ml.html
Thanks RT. I replaced my OEM batteries in March just because they were 8 years old. In the 8 years the three batteries worked fine. I had some voltage problems before I replaced the batteries and after many posts decided the issue might be the separator so I replaced it with the same one.
I will test the separator next week although the drain on the coach batteries is about what it should be. However, the 1.4 amp drain on the engine battery is a surprise
 

icarus

Well-known member
Not to belabor what my be obvious, but are you sure you wired the isolator relay the "right" way? In other words the relay normally draws its current off the house batteries. If you wired it "backwards" it would draw current off the vehicle battery. Since the current draw seems to be just about what we know the relay draws, it certainly is worth looking at.

Icarus
 

gte

2008 RS
Icarus
I put the wires from the old separator on the same terminals on the new one, but I will check.
Great suggestion since it is always the little things that getcha
 

BobLLL

Active member
You can easily disconnect the ground terminal of the separator, and that will eliminate any draw by it. If you still have your excessive chassis draw, look elsewhere for the problem.
 

BobLLL

Active member
Also, if the separator has become stuck in the on position, and drawing its 1.5 "drive" current for any length of time, it will be quite warm to the touch.
 

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