Parasitic loading of the starter battery

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Parasitic loading of the starter battery

November 10, 2011, 08:58:38 am

Greetings,

My coach has been parked most of this year while repairs and renovations have gone on. I've noted the starter battery charge needs to be topped up fairly regularly. While the battery bay was being made over, I connected an ammeter to both sets of batteries to see what, if anything, the parasitic loading might be with everything off. While the coach batteries showed nothing, the starter battery showed a draw of 75 mA in the cable going to the DC bus in the battery bay. I know the dash clock consumes power. The new in-dash CD player is wired to coach power, as far as I can tell. Can't think what else might be drawing power.

At any rate, it strikes me that this is an issue that needs addressing, especially as I plan to boondock a fair bit. While I can disconnect the battery cable, don't like the idea of a loose cable floating around, nor do I like repeatedly connecting and disconnecting the same terminals. Best I've come up with is to install a battery disconnect switch on the line going from the positive terminal of the starter battery to the DC bus. In this way the parasitic loading is eliminated. It also serves as somewhat of theft deterrent, as the ignition switch draws power through that line, if I'm not mistaken.

I've ordered this marine disconnect switch, rated at 175 amps continuous (way more than enough I should think), ignition protected (ie sealed box), and a luminous label, from Amazon, for $24 --> Amazon.com: Blue Sea Systems 6006 m-Series (Mini) Battery Switch Single Circuit . To facilitate connection, also purchased a preterminated 2/0 battery cable from McMaster Carr ($19). Switch will be mounted on the side wall behind the fibergalss DC bus cover.

Near as I can determine, this won't hurt anything. Does anyone see any issues making this mod? Thanks.

Steve

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Re: Parasitic loading of the starter battery

Reply #1 – November 10, 2011, 09:11:21 am

As long as you don't run the very high amp draw wire to the starter through it, you will be fine.

But, .075a draw is really only an issue when storing the coach-- virtually insignificant compared with other draws when using the coach/boondocking.

The two solutions are to disconnect when in storage OR to charge it. Charging can be done with an Xantrex Echo Charger, Trik L Charge (if you have 120 VAC where you store it), etc or with a solar panel.

You could also start pulling fuses to identify the sources of that .75 amp draw and perhaps just use an inexpensive switch to isolate those items.

Brett

Re: Parasitic loading of the starter battery

Reply #2 – November 10, 2011, 09:39:11 am

My 93 GV has a Ford cruise that is always on. Gave up trying to figure out what else might be on so I just lift up the step and pull off the cable. Store it all winter and it fires right off in the spring.

Bill and Doris
OKC
93 GV (gas)

Re: Parasitic loading of the starter battery

Reply #3 – November 10, 2011, 09:40:02 am

Thanks Brett.

The starter is fed by another cable from the positive terminal of the starter battery. As long as I don't do any switching with the engine running or the levelling system active I should be ok (I think). I also like the idea of the theft deterrent aspects (those old GM ignition switches are easy to get past).

Have been charging the battery periodically, but that's becoming a nuisance (no generator onboard at the moment, and the inverter/charger is not installed yet). Winter's coming, and she'll be parked soon until spring. Am hoping to add solar panels at that point.

Something regarding keeping the starter battery charged - I have read of suggestions of various devices to connect to the starter battery to trickle charge it when camped out. But in the Sping 2011 Motorcader magazine, Mark Harvey wrote an article about testing the boost solenoid, and he indicated that you can use the boost switch to charge both the coach and starter batteries simulataneously when shore power is available or the gennie's running. He also indicated that FT can install a voltage sensitive relay to automatically charge the starter battery during these times, which eliminates using the boost switch.

Have not seen anyone mention or comment on that, but it seems like a simple way to keep that starter battery topped up, without having to do anything else.

Steve

Re: Parasitic loading of the starter battery

Reply #4 – November 10, 2011, 09:42:19 am

Quote from: spoiled122843 – November 10, 2011, 09:39:11 am

My 93 GV has a Ford cruise that is always on. Gave up trying to figure out what else might be on so I just lift up the step and pull off the cable. Store it all winter and it fires right off in the spring.

Bill and Doris
OKC
93 GV (gas)

Thanks Bill.

I remember very recently reading (was it posted here??) about storing batteries in winter. Charge 'em up before storage, and they'll do fine in the cold weather. It's the hot weather that leads to a higher self-discharge rate. Interesting stuff.

Steve

Re: Parasitic loading of the starter battery

Reply #5 – November 10, 2011, 09:47:13 am

Quote from: Merle Hench – November 10, 2011, 09:40:02 am

Thanks Brett.

Something regarding keeping the starter battery charged - I have read of suggestions of various devices to connect to the starter battery to trickle charge it when camped out. But in the Sping 2011 Motorcader magazine, Mark Harvey wrote an article about testing the boost solenoid, and he indicated that you can use the boost switch to charge both the coach and starter batteries simultaneously when shore power is available or the gennie's running. He also indicated that FT can install a voltage sensitive relay to automatically charge the starter battery during these times, which eliminates using the boost switch.

Have not seen anyone mention or comment on that, but it seems like a simple way to keep that starter battery topped up, without having to do anything else.

Steve

Steve,

Yes, the boost/combine switch can activate the boost/combine solenoid to connect the chassis to house battery banks. That allows the converter or inverter/charger which charges only the house battery to charge the chassis battery as well through the connection in the boost/combine solenoid. I see this as a reasonable emergency or short-term solution.

The Xantrex Echo Charger is a high quality "voltage sensitive relay to automatically charge the starter battery during these times" (Battery Chargers | Auxiliary Battery Charger | Xantrex) and IMO would be a much better permanent solution.

Re: Parasitic loading of the starter battery

Reply #6 – November 10, 2011, 09:51:39 am

Steve,

We are at least the third owner of our coach. Hard to think it is almost 20 years old but guess not much to keep the sun from rising and setting. During it's life, there have been numerous changes and component replacements. In our case a simple cable mistake an owner or two earlier made when changing out the isolator coupled with the boost solenoid failure (stuck on) made a huge difference in the way the electrical system worked. Frequently, a new accessory is wired into the most available 12 volt source. Sometimes, these changes can go unnoticed for years but, in your case, could be a mysterious reason why the engine batteries go flat (and don't last as long) when leaving the rig unattended for a length of time. Like Brett said, you can start pulling fuses. Remember the fuses back in the stateroom and there are also a couple in the overhead compartment above the driver. Check the radio 12V source again as most have a volatile memory and use a little juice all the time. Remember the second radio aft. Analog clocks also use a lot more than the new digital ones.

Re: Parasitic loading of the starter battery

Reply #7 – November 10, 2011, 03:05:06 pm

I have left the boost switch on during storage while plugged into shore power at home. I've done that with good results for almost 18 months. Something like the Xantrex Echo Charger would be a superior solution.

I recently added a Battery Tender charger for the chassis battery and no longer leave the boost switch on. The Battery Tender can be plugged into an outlet off the inverter or an outlet among the circuits that are only powered by shore power or generator. It is a solution that might be applicable in some situations. It could keep the chassis battery fully charged from the inverter. That charge would be at the expense of power from the chassis batteries. Plugged to either supply, it will help keep the chassis battery charged if the coach is on shore power or generator power.

The Battery Tender provides an easy solution to maintaining charge of batteries that spend a lot of time "waiting to serve." I have one for each of my motorcycles. They have helped provide good service from batteries that spend a lot of time between starts.

Re: Parasitic loading of the starter battery

Reply #8 – November 10, 2011, 05:59:52 pm

75mA is just 0.075A, this is practically nothing as far as your batteries are concerned. Your internal battery leakage current might be higher. Do the math and calculate how long it would take to discharge your batteries at that rate.

Re: Parasitic loading of the starter battery

Reply #9 – November 10, 2011, 06:35:38 pm

Small tid bit, remember a dome light in a car will kill the car battery in a day or over night.
Most auto batteries drain them selves at approx. 50ma. we set some chargers at 65 ma charge to keep them cheerful over long term, will bring voltage up to 12.90-12.95 VDC after a few months.

Re: Parasitic loading of the starter battery

Reply #10 – November 10, 2011, 07:26:06 pm

Thanks for the replies folks.

I tried disconnecting the "always on" wire to the CD player. No difference. I used the original Sony wire connections - it will not turn on unless coach power is on.

Thankfully neither previous owner mucked with the electrics, save the last fellow who ran coax cable all over the place, which I'm still finding and removing. (Why would he run a coax cable into the engine bay?

)

I didn't think 75ma was a whole lot of current either, but it will drain the battery over a period of several weeks. Going to install the cutoff switch and be done with it. If it will be parked again for any period of time unused, switch off and the battery stays charged. Simple.

Checked out the Xantrex echo charger. Am installing a Magnum Inverter, so checked Magnum's site, and found a Battery Combiner which works in the same manner, but features adjustable setpoints and will divert 25 amps of current vs Xantrex' 15 amps. Planning out the inverter install layout now; guess I'll add one more module. Link --> ME-SBC Smart Battery Combiner

Going to look into this a little more. Thanks again good people.

Steve

Re: Parasitic loading of the starter battery

Reply #11 – November 10, 2011, 07:53:46 pm

Quote

(Why would he run a coax cable into the engine bay? )

He might have at one time had a camera mounted in the engine bay to observe while driving. My guess???

Re: Parasitic loading of the starter battery

Reply #12 – November 11, 2011, 07:26:28 am

I don't think so, but maybe. He coiled it up and tied it off. Terminal was badly oxidized. I found a coax connection in almost every bay, even in the tank drain bay. This guy really liked his TVs, whether inside or out, on both sides of the coach.

Steve

Re: Parasitic loading of the starter battery

Reply #13 – November 11, 2011, 07:32:53 am

Quote

The Xantrex Echo Charger is a high quality "voltage sensitive relay to automatically charge the starter battery during these times" (Battery Chargers | Auxiliary Battery Charger | Xantrex) and IMO would be a much better permanent solution.

Why is this better than a Trik-L-Charge, Btett?

Re: Parasitic loading of the starter battery

Reply #14 – November 11, 2011, 09:16:17 am

Quote from: Duane Budd – November 11, 2011, 07:32:53 am

Quote

The Xantrex Echo Charger is a high quality "voltage sensitive relay to automatically charge the starter battery during these times" (Battery Chargers | Auxiliary Battery Charger | Xantrex) and IMO would be a much better permanent solution.

Why is this better than a Trik-L-Charge, Brett?

Duane,

The discussion was about leaving the boost switch/solenoid on 24/7. Either the Xantrex Echo Charger or Trik-L-Charge are better permanent solutions IMO.

Re: Parasitic loading of the starter battery

Reply #15 – November 11, 2011, 09:18:52 am

Steve, I saw a coax nest in one other FT. The couple lived in it and had a yard mounted dish, he ran cable to all the TVs from the yard dish and it was really a nest. He was surprised when I showed him the permanent hookups for cable etc. Go figure
Gary B

Re: Parasitic loading of the starter battery

Reply #16 – November 11, 2011, 12:22:55 pm

Putting a disconnect switch on a start battery has disadvantages...

The starter's cable post is a relay point for other start battery loads. Since your new disconnect switch will be at battery it will carry starter load, which may self-destruct switch and prevent full current to starter. Also keep in mind that anything that disconnects alternator loads can be damage things.

We and many others have been using a simple to install diode-based $50 Trik-L-Start to keep start battery charged.

Diode based battery bank combiners do not work if batteries are 100 degrees due to hot weather or enclosed battery compartments. Temperature compensated battery chargers will correctly float charge hot GEL house batteries at about 12.9 - 13.0 volts.
Diode based combiners have about a 6/10 of a volt output reduction, so hot start batteries will not get charged.

We ran into this problem last summer in Texas, so I started exploring automatic relay combiners that use voltage logic circuit boards to connect & disconnect at specific voltages.

These relay combiners directly connect both battery banks with the same charge voltages.

My first relay combiner purchase from Magnum caused interference with an Allison supply cable which caused start problems in our coach. I am now looking at another relay combiner that has an ignition isolation feature that can be used to disconnect combiner when engine is running and allow automatic combining when engine is shut off. I will let write-up my findings after I install the relay.

Meanwhile I am manually disconnecting our Magnum relay combiner before starting engine and also using boost switch to keep start battery charged when parked or doing nothing for short stops.

Re: Parasitic loading of the starter battery

Reply #17 – November 11, 2011, 10:28:28 pm

Quote from: Barry & Cindy – November 11, 2011, 12:22:55 pm

Putting a disconnect switch on a start battery has disadvantages...

The starter's cable post is a relay point for other start battery loads. Since your new disconnect switch will be at battery it will carry starter load, which may self-destruct switch and prevent full current to starter. Also keep in mind that anything that disconnects alternator loads can be damage things.

There are two positive battery cables coming off the starter battery in my coach. One goes back to the engine bay/starter/alternator, the other to the DC bus in the battery bay. It is the one going to the DC bus that I am adding the switch to, not the one to the starter. If I am correct, the connection to the DC bus powers the ignition switch. With no power there, the coach cannot start.

The idea is to switch off when parked for storage or if the coach will be idle for a time. The battery stays charged (aside from self-discharge) as there is no load on it. When it's time to climb aboard and head out, you switch on. In normal use the switch stays on all the time. Just seems simpler to eliminate the drain when idle than to keep charging the battery. Or am I missing something?

I'm likely going to get the Magnum combiner to keep the starter battery charged when camped out. Whenever the inverter is charging the coach batteries, the start battery gets topped up if it needs it. Adding a switch or relay is a good idea to disable the combiner when driving. The ignition being on is a good trigger to energize a relay to disable it. More stuff to think about...

Steve

Re: Parasitic loading of the starter battery

Reply #18 – November 11, 2011, 11:23:15 pm

Putting the start battery disconnect switch will work. I don't know what other loads there may be other than those on the bay DC bus. All batteries have some loss of capacity over time even without any loads. Some type of combiner may still be needed after a while.

I don't recommend the Magnum relay combiner any more after it messed with my transmission neutral start relay. Also Magnum Combiner is not weather proof so it cannot be easily added near the isolator or boost solenoid. I like Magnum products, but their tech support was no help with my Combiner problems.

Re: Parasitic loading of the starter battery

Reply #19 – November 12, 2011, 09:46:07 am

Thanks for the feedback Barry.

Am doing a Magnum inverter install under the fridge, where the central vac used to be - right on top of the battery bay. That area is open to ventilation but not likely to get wet. Installing the inverter, gen start module, and battery monitor in there. Was thinking that would also be the spot for the combiner.

Would not want the combiner active when the engine is running and the alternator charging, especially based on what you've mentioned with the neutral start relay. I'd only want it active when parked. A double pole switch which cuts both lines from the combiner to the batteries seems like the simplest way to do it. An automated solution would be nicer, but more complex. Going to see what I can come up with on this.

I do dislike so many exposed electrical connections in the belly of the bus. Spent a fair bit of time cleaning all the corrosion from the battery isolator terminals and posts, and other components in that area. It's the same with my hydraulic HWH levelling system - all the solenoid connections are exposed under the coach. When one solenoid, then another stopped working the fix was again to clean all the connections of corrosion. HWH recommends Krylon 1307 Battery Protector, which I'll be using to seal the connections on everything under there --> Krylon® Battery Protector - Krylon Products Group .

Steve

Re: Parasitic loading of the starter battery

Reply #20 – November 12, 2011, 12:34:23 pm

Steve,

Nice that your electronics are in a dry place. We left the lower side & roof propane fridge vents in place, which means our electric fridge back is open to the weather. Your electronics under the fridge floor could be impacted by a hard rain or overflowing fridge auto defrost evaporation pan. So you may want to seal bottom weather tight and put a piece of plastic under the 'roof' of your under fridge electronics area.

Magnum has a very nice true-sine wave inverter. I think their products are well thought out. Using a Magnum inverter allows you to use the networked version of the Magnum gen start to better integrate auto gen start into your coach 12-volt system. I assume your battery monitor will be Magnum, too.

We have two house batteries and early-on found that one battery was 'open' and did not take a charge or supply power, but it was not obvious as all looked well. Without knowing we had half-capacity, I installed separate shunts on each battery with an inexpensive milli-volt meters so I could monitor how each battery was contributing to house power discharge & charge. To my great surprise, I learned about our dead battery. I am planning to put separate state-of-charge meters to monitor each house battery, replacing my milli-volt. Without separate shunts on each battery, it pretty much is impossible to know how each battery is contributing to the total demand, but a single state-of-charge meter may show that something is lacking.

Your combiner disconnect relay idea could just disconnect one of the three Magnum combiner leads, maybe the ground lead to disable combining. Normally closed relay points with coil transfer on ignition power would make more sense because keeping batteries combined during dry camping (with solar?) would not use any power.

Re: Parasitic loading of the starter battery

Reply #21 – November 12, 2011, 03:37:01 pm

Thanks Barry.

I've wondered about water getting in the fridge side wall vent. Can see bugs getting in, so I screened it from the inside. I did not consider the fridge evaporation pan overflowing. Thank you for bringing that up - will need to make accomodations in how I construct the fridge support floor. Do love that new Whirlpool.

Have already sealed, and insulated the entire fridge bay area. Was going to make an opening near the front of the fridge floor, just above the intake to the Magnum cooling fan. It would draw air in from under the fridge and exhaust it out the opening in the floor in the back and out the roof vent.

It is all Magnum down below, with the advanced remote. I decided on the 2800 watt pure sine wave model. Only $100 more than the 2000 watt model. What the heck... Am hoping to be able to add 4 or more solar panels with charge controller in the spring.

Good call on the combiner. Disconnecting just the ground wire would do it. And a normally closed relay is what I had in mind. For now though, I'm thinking a switch, perhaps in the battery bay next to the other one.

With all the electronics going in, new fridge and roof A/Cs, plus the recording equipment I'm adding, I decided to protect myself against shore power issues, and am now adding a Surge Guard Plus with remote. Good a time as any, as I have to repanel the electrics with the inverter being added. About to go cut a big hole in the end of the bed, and redo it to accomodate two new main breaker panels.

Got that switch installed. Tested it out. Switched off - the ignition relay/solenoid is dead. Nothing happens when you turn the key. No power at all at the dash. Solves the issue. I think it is a good theft deterrent as well, although I don't know that a lot of coaches get stolen(?).

Steve

Re: Parasitic loading of the starter battery

Reply #22 – November 12, 2011, 03:43:50 pm

When you do the fridge compartment, check the wood piece that supports the bottom of the outside opening fridge vent. Mine was rotten from water getting in.

Re: Parasitic loading of the starter battery

Reply #23 – November 12, 2011, 03:46:18 pm

Thanks Pierce. I saw evidence of that too. Scraped the old sealant off around the opening, applied waterproof foil tape all around, and resealed the seam with silicone caulk.

Steve

Re: Parasitic loading of the starter battery

Reply #24 – November 13, 2011, 09:36:19 am

Just wanted to add something regarding the switch installed - I double-checked the DC schematic for my coach. The cable to which I added the switch, which connects to one side of the boost solenoid, also receives the charge current from the alternator via the isolator. Thus the switch should be sized to handle a minimum of the maximum alternator output. My alternator is rated at 160 amps (I think - no more than that). The switch installed is spec'ed at 175 amps continuous, 350 amps intermittent, so is adequate to the task.

BTW - the starter battery had been charged 3 weeks ago. Checked it after the mod, and found it at 11.8 volts. That tiny bit of current will drain the battery completely over 5 or 6 weeks. Might last longer with an 8D, but I have a 27F Optima Yellow top as a starter battery.

Steve

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