Engine battery drain

Topic: Engine battery drain (Read 1722 times) previous topic - next topic

Engine battery drain

May 31, 2020, 07:41:05 pm

The coach has an echo battery tender that doesn't seem to keep up. For some reason the batteries aren't staying up. Today we took the negative cable off the engine battery and connected a DVM between it and the the negative post. With the key off it was drawing what showed to be 16.2 amps. I don't know how it didn't pop the fuse in my meter. What could be drawing that much with the key off? Or ami reading/using my meter wrong?

Re: Engine battery drain

Reply #1 – May 31, 2020, 07:51:34 pm

Possible alternator or isolator

Re: Engine battery drain

Reply #2 – May 31, 2020, 08:07:01 pm

No, μ, the letter Mu; stands for "micro" or "one millionth". It's Greek.

Pierce

Re: Engine battery drain

Reply #3 – May 31, 2020, 08:22:23 pm

Quote from: Pierce & Gaylie Stewart – May 31, 2020, 08:07:01 pm

No, μ, the letter Mu; stands for "micro" or "one millionth". It's Greek.

Pierce

Thanks Pierce, I see the giant orange capital A two clicks over now. 🤯 I was using a different one earlier today at the house on my Jeep because it decided it wants to do the same thing. It sparked pretty good when I touched the lead to it. I'll go back tomorrow and check it again properly.

Re: Engine battery drain

Reply #4 – May 31, 2020, 09:34:00 pm

There went all my credibility. I thought it was strange it was exceeding the maximum of 10a without any pops or smoke.

Re: Engine battery drain

Reply #5 – June 01, 2020, 08:43:49 am

Quote from: DJ and Jane – May 31, 2020, 09:34:00 pm

There went all my credibility. I thought it was strange it was exceeding the maximum of 10a without any pops or smoke.

Cheap learning experience. You rally don't want to know how much the quick blow fuse in a Fluke multimeter costs.

If your battery tender doesn't keep up, it's because the internal leakage in the battery is too high. Disconnect the ground terminal from the battery and check again after 24 hours.

Expanded:

Lead acid battery voltage measurements are only valid after 3 hours of rest due to the sluggishness of the battery chemistry. So disconnect the negative cable to isolate your battery from the load, wait 3 hours and measure the voltage. Wait 24 hours and measure the voltage again. If the battery resting voltage has changed for the worse buy a new battery. If not buy a new RV. Or find out where the electricity is going.

Re: Engine battery drain

Reply #6 – June 01, 2020, 10:15:50 am

Quote from: Old Toolmaker – June 01, 2020, 08:43:49 am

Cheap learning experience. You rally don't want to know how much the quick blow fuse in a Fluke multimeter costs.

If your battery tender doesn't keep up, it's because the internal leakage in the battery is too high. Disconnect the ground terminal from the battery and check again after 24 hours.

Expanded:

Lead acid battery voltage measurements are only valid after 3 hours of rest due to the sluggishness of the battery chemistry. So disconnect the negative cable to isolate your battery from the load, wait 3 hours and measure the voltage. Wait 24 hours and measure the voltage again. If the battery resting voltage has changed for the worse buy a new battery. If not buy a new RV. Or find out where the electricity is going.

Thank you. I didn't think to check the voltage yesterday when I disconnected it. I did exactly that on my Jeep yesterday. I did stop by this morning and check the draw with the DVM on the correct setting and I got .173A and the voltage is at 12.24. I'll check again tomorrow. How much draw is acceptable with the key off?

Re: Engine battery drain

Reply #7 – June 01, 2020, 11:41:03 am

Quote from: DJ and Jane – June 01, 2020, 10:15:50 am

...... the draw with the DVM on the correct setting and I got .173A and the voltage is at 12.24. I'll check again tomorrow. How much draw is acceptable with the key off?

Draw can be from alarm system, radio memory, keyless entry, etc. so it varies with individual vehicles.

One amp = 1000 milliamps. You have 173 milliamps. This sounds like double what is considered high if your reading is accurate. I do not know what you are powering. You might check your owners manual for the vehicle. I remember having one vehicle., manual said to turn off keyless entry if parked more than two weeks. No easy answer to your question. I hope this helps.

"A normal amount of parasitic draw for newer cars is between 50-milliamp to 85-milliamp current draw. A normal amount of parasitic draw for older cars is a reading less than 50-milliamp. Anything past these amounts indicates an electrical issue and should be addressed by a mechanic."

Re: Engine battery drain

Reply #8 – June 01, 2020, 01:43:18 pm

Thanks Jack it does help, I had it on the big orange capital A this time. I held the leads on there close to a minute I'd say to see if it would go lower. When I do it on my Jeep it will be at 1-200 milliamps then within a few seconds it will drop off to about 30 or maybe less even. I will start looking for something that's drawing that shouldn't be. Does the ecm draw all of the time?

Re: Engine battery drain

Reply #9 – June 01, 2020, 02:41:42 pm

The ECM generally gets power from the ignition switch being activated.

My solution to your same issue was to put in a new AGM, Odyssey battery. Afterwards I installed a battery cutoff to totally protect my new battery.

So maybe look at the Odyssey, or something like the best AGM battery from Napa, Oriellys, Interstate, or Autozone. They will run approx $200.

https://www.autozone.com/ignition-tune-up-and-routine-maintenance/battery

Re: Engine battery drain

Reply #10 – June 01, 2020, 03:16:04 pm

Quote from: DJ and Jane – June 01, 2020, 01:43:18 pm

. Does the ecm draw all of the time?

Yes, Both engine and transmission memory in the ECM use power unless you unhook the batteries

Mike

Re: Engine battery drain

Reply #11 – June 01, 2020, 04:27:07 pm

The electric system for the engine is not optimized for a AGM. The float voltage is as I understand it is different for a a flooded cell versus an AGM.

Probably why the oem alternator had and adjustable voltage that Wolfe has mentioned adjusting to be at 13.6 volts float.

RSL(run, start, lighting) batteries are normally higher voltage than agm's.

Bmw's come with AGM batteries. The float voltage as I understand it is set lower than flooded cells used in other cars.

Running higher voltage into agm's may be overcharging them over the long run.

This info came from my Lexus boards as to why Lexus did not equip my 12 year old model with an AGM versus a sealed VRLA battery.

Like I posted this maybe why the adjustable voltage alternator was being used?

Food for thought

Re: Engine battery drain

Reply #12 – June 01, 2020, 05:19:11 pm

Quote from: Pamela & Mike – June 01, 2020, 03:16:04 pm

Yes, Both engine and transmission memory in the ECM use power unless you unhook the batteries

Mike

My 96 U320 has the engine and transmission connected directly to the battery. Disconnecting the Neg cable from coach's chassis ground will not disconnect the control modules if they are connected directly to the positive negative battery terminals.

Re: Engine battery drain

Reply #13 – June 01, 2020, 08:14:13 pm

Quote from: TGordon – June 01, 2020, 05:19:11 pm

My 96 U320 has the engine and transmission connected directly to the battery. Disconnecting the Neg cable from coach's chassis ground will not disconnect the control modules if they are connected directly to the positive negative battery terminals.

I put a cutoff switch on the negative battery cable.
With it on off, nothing passes from the batteries.

I did this when I replaced my batteris with Exide AGM grp 34 Edge batteries. I am very happy with these. Exide changed the name now to Exise Max.

I added a short, stiff, extension cable and the following switch, which did not require a mounting bracket. The Blue Sea switch has 1/2 inch studs and is rated for 600 amps since the starter could posibly draw over 400 amps.
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Re: Engine battery drain

Reply #14 – June 01, 2020, 09:47:11 pm

Quote from: Jack Lewis – June 01, 2020, 08:14:13 pm

I put a cutoff switch on the negative battery cable
With it on off, nothing passes from the batteries.

That's what my brother is telling me to do. I like the idea of it. I would have to run a longer cable and do away with one of the grounds. MOT put another one on there trying to help the starter out. You have to get up underneath the coach to get to the batteries. It's not very convenient. At the same time I feel like the batteries shouldn't drain that fast. Also, we've got the red top optimas which are agm also. Have been in there about two years now I think.

Re: Engine battery drain

Reply #15 – June 02, 2020, 09:02:00 am

DJ and Jane wrote: "...... the draw with the DVM on the correct setting and I got .173A and the voltage is at 12.24."

010 You could install a suitably rated master control relay with a toggle switch and a red guard.

Let's do the math. With labels.

.173A(1 Hour) = .173 Amp Hour.

A BCI Group 31 battery holds about 100 amp hours. If we set a lower limit of 50 amp hours then

50 amp hours divided by .173 amp hour = 289 hours after you cancel out the amp labels.

Since I'm feeling snarky this morning, although the coffee is nearly ready, 289 hours divided by the 24 hours in a standard* day gives us 12 days.

GOTO 010

* Listening to scientists, especially astronomers can really mess up your mind, from, the earth's got the jitters, to the earth moved in relationship to the sun and the stars while spinning about its axis.

Re: Engine battery drain

Reply #16 – June 02, 2020, 01:35:33 pm

Running a start battery down at all unless designed to be deep cycle will quickly damage it.

Hence the industry wide use of auto combiners for battery banks

I have found no other way to 100% reliably charge the engine batteries.

Had 2 different chassis batteries chargers fail. Two sets of batteries killed dead

Re: Engine battery drain

Reply #17 – June 02, 2020, 01:57:24 pm

Agree, battery combiners are one option.

So are low amp, stand alone 120 VAC smart chargers dedicated to the chassis battery bank. Yes, only if you have 120 VAC where you store the coach.

Either option will keep them charged.

Re: Engine battery drain

Reply #18 – June 02, 2020, 02:05:45 pm

As I said I had 2 dedicated 110 volt chargers fail. One was a trickl charger. Green light on. No output.

Too expensive if you are using nice batteries

Re: Engine battery drain

Reply #19 – June 02, 2020, 02:07:54 pm

Quote from: wolfe10 – June 02, 2020, 01:57:24 pm

Agree, battery combiners are one option.

So are low amp, stand alone 120 VAC smart chargers dedicated to the chassis battery bank. Yes, only if you have 120 VAC where you store the coach.

Either option will keep them charged.

I actually did end up putting a 110v battery tender on there and it was keeping up pretty well. But no power where it's at.

Re: Engine battery drain

Reply #20 – June 02, 2020, 02:09:16 pm

I'm gonna run over today and see what the voltage is down to. The more the wheels turn in my head, where it doesn't have power the cutoff would be best

Re: Engine battery drain

Reply #21 – June 02, 2020, 02:12:18 pm

If you have the ability to keep the battery charged (120 VAC, solar, etc) that IS preferable to disconnecting them.

The transmission and engine computers prefer to have their memory lead (notice TWO fuses to Allison ECU-- the 5 amp one for memory) stay hot.

Re: Engine battery drain

Reply #22 – June 02, 2020, 02:29:54 pm

Quote from: wolfe10 – June 02, 2020, 02:12:18 pm

If you have the ability to keep the battery charged (120 VAC, solar, etc) that IS preferable to disconnecting them.

The transmission and engine computers prefer to have their memory lead (notice TWO fuses to Allison ECU-- the 5 amp one for memory) stay hot.

I thought of a solar panel too. I would like to keep them up.

Re: Engine battery drain

Reply #23 – June 02, 2020, 03:10:24 pm

I checked the voltage on the engine batteries. They're at 12.20v. Yesterday when I disconnected them they were at 12.24.

Re: Engine battery drain

Reply #24 – June 02, 2020, 03:13:03 pm

Those readings show a 50% discharged battery (assuming they are on good condition.

Time to recharge!

Worse case, use the boost switch and shore power or generator to power the inverter/charger.

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