12 VDC Batteries and Charging

[wolfe10]

Tools needed: Digital Voltmeter (start under $20 from Sears, Radio Shack, etc).

There is a lot of confusion about batteries and what charges them. There are some conventions followed by all manufacturers, but there are enough differences that one can not categorically say “They are all like this.â€

All coaches do have two battery banks, HOUSE and CHASSIS. House batteries are/should be deep cycle and supply the 12 VDC needs of house items like lighting, water pump, fans, furnace, refrigerator PC board, water heater PC board, etc. Generally made up of multiple batteries��" either 12 VDC batteries wired IN PARALLEL or 6 VDC batteries wired IN SERIES (or pairs in series wired in parallel��"4, 6 etc batteries). Think of 6 volt batteries wired in series as “a 12 volt battery in two cases,†as all house functions are 12 VDC. Generally the house battery starts the generator, but a few use the chassis battery or have a separate generator battery.

The chassis battery starts the engine and in a few, the generator as well. They are starting batteries, not deep cycle batteries.

So, how do they get recharged-- two ways on most coaches��"from the alternator when the engine is running and from the converter, charger or inverter/charger when 120 VAC is available from shore power or generator.

With the engine running, most coaches charge BOTH battery banks. This is generally done through a battery isolator so that the two battery banks are not left connected when the engine is not running which would run down both banks. The isolator can be a diode-based isolator, a simple solenoid (large relay) or a smart relay. All do virtually the same thing, allow both battery banks to be charged from the alternator but separate them when the engine is not running.

You should periodically VERIFY that indeed the wiring and “isolation device†are working and that both battery banks are being charged by the alternator. Start by disconnecting from shore power/generator for several hours. At the batteries, check voltage. If you have 6 VDC batteries, check from the positive terminal with cable going to house to negative with cable going to house, not the positive/negative with cable that just goes from one battery to the other. Do the same for the chassis battery bank. Voltages should be between 12.2 VDC (50% discharged battery) and 12.7 VDC (fully charged battery). Anything above 12.7 is surface charge and will quickly go away with even light loads. Note the voltages.

Now, start the engine. If you have the feature, go to high idle (same as you do to warm up the engine after 30 seconds at low idle). Go back and read voltage at the batteries. Both banks should be higher than the last reading and if the batteries are not deeply discharged, between 13.5 and 14.5 VDC. If this is not the case, you will need to troubleshoot your charging/isolation system.

With 120 VAC from shore power or generator, the converter, charger or inverter/charger should also charge the house bank and on many the chassis batteries as well. To verify, disconnect from shore power/generator for several hours. Read voltage at house and chassis batteries. Plug in/turn on generator. Read voltage. Voltage at any battery receiving a charge should go from under 13 VDC to 13.2-14.2 VDC. If it remains the same, that bank is not being charged. Many coaches do not charge the chassis battery from shore power��" a serious problem with all the parasitic loads on today’s chassis battery. IMO, this should be corrected. Xantrex Echo charger, a separate “small smart charger for chassis bank, solar panel, or even wire from house positive to chassis positive all work to keep the chassis battery charged. If using a wire from positive to positive, BOTH ends must have a fuse, since touching any metal or ground terminal with either end would cause a dead short. Do NOT use a wire if one bank is deeply discharged and the other fully charged, as small wires are not designed to handle the rapid transfer of large amounts of current��"this is for maintaining a charge only.

You also have a battery boost/combine switch. This allows the two banks to be combined, with house battery assisting the chassis battery in starting the engine or the chassis battery assisting the house battery in starting the generator. To verify its functioning, disconnect from shore power/generator for several hours. Turn on some 12 VDC loads to slightly discharge the house battery. Read battery voltage at each battery��"all you are really looking for is that they are different. Now, with someone activating the boost switch, verify that both batteries are at exactly the same voltage. If not, you need to troubleshoot and determine if the switch/wiring or solenoid is faulty.

If the battery voltages were not the same with the boost switch activated, locate the combine solenoid. It should be near the batteries and have a large cable going to each battery bank. Recheck voltage from each large lug to ground��"with solenoid working, they should be exactly the same. It will also have either one or two small wires to it. If two, one will be the signal wire and the other a ground. If one small wire, it will be the signal wire from the dash switch, and the solenoid grounds directly from metal to metal contact. With your voltmeter or even a test light, check for 12 VDC/light at the small signal wire lug to ground. If present, but the voltage at the two large lugs is not the same (i.e. batteries not combined), the solenoid is defective. If you did not get 12 VDC/light from the signal terminal with boost switch activated you need to check the dash switch and wiring and you still need to verify that the solenoid is working. With a small wire (will only be carrying less than one amp) go from either large lug to the small signal wire lug (not ground lug). If the solenoid is functioning, you should hear a loud “click†and the two large lugs should read the same voltage.

[peepafox]

All:

I have been reading what Wolfe states on battery charging both coach and house. I would like to add my experiences on this subject. On my Monaco Windsor I have replaced the isolator relay (when it was under warranty) 4 times with the White-Rodgers solenoid PN 586-10511-3 12 volts continuous (Monaco supplied). The fault of these relays is that they would pull in when the relay coil was activated but the contact resistance was too high to connect the batteries as they were close in voltage so only low current would be flowing. Now that the warranty is over I replaced that relay with a Napa PN 85-120. It has been working correctly for about 18 months now.

My coach system for activating the isolator relay is somewhat more complex that I have read in the forums.

On the coach power control circuit board (located in a cabinet in front of the left front wheel there are two relays in series. The first is a time delay relay that activates about 60 seconds after the engine is running. This is to be sure that the alternator is charging the chassis batteries. In between it and the isolation relay is a second relay that in its normally closed position allows the first relay to active the isolation relay. This second relay is active when the generator or shore power is available and turns off the isolation relay so the inverter and alternator do not fight each other.

Just to say that the isolation relay is subject to fail at conducting current between the two battery systems.

Larry

[joemar1112@yahoo.com]

Tools needed: Digital Voltmeter (start under $20 from Sears, Radio Shack, etc).

There is a lot of confusion about batteries and what charges them. There are some conventions followed by all manufacturers, but there are enough differences that one can not categorically say “They are all like this.â€

All coaches do have two battery banks, HOUSE and CHASSIS. House batteries are/should be deep cycle and supply the 12 VDC needs of house items like lighting, water pump, fans, furnace, refrigerator PC board, water heater PC board, etc. Generally made up of multiple batteries��" either 12 VDC batteries wired IN PARALLEL or 6 VDC batteries wired IN SERIES (or pairs in series wired in parallel��"4, 6 etc batteries). Think of 6 volt batteries wired in series as “a 12 volt battery in two cases,†as all house functions are 12 VDC. Generally the house battery starts the generator, but a few use the chassis battery or have a separate generator battery.

The chassis battery starts the engine and in a few, the generator as well. They are starting batteries, not deep cycle batteries.

So, how do they get recharged-- two ways on most coaches��"from the alternator when the engine is running and from the converter, charger or inverter/charger when 120 VAC is available from shore power or generator.

With the engine running, most coaches charge BOTH battery banks. This is generally done through a battery isolator so that the two battery banks are not left connected when the engine is not running which would run down both banks. The isolator can be a diode-based isolator, a simple solenoid (large relay) or a smart relay. All do virtually the same thing, allow both battery banks to be charged from the alternator but separate them when the engine is not running.

You should periodically VERIFY that indeed the wiring and “isolation device†are working and that both battery banks are being charged by the alternator. Start by disconnecting from shore power/generator for several hours. At the batteries, check voltage. If you have 6 VDC batteries, check from the positive terminal with cable going to house to negative with cable going to house, not the positive/negative with cable that just goes from one battery to the other. Do the same for the chassis battery bank. Voltages should be between 12.2 VDC (50% discharged battery) and 12.7 VDC (fully charged battery). Anything above 12.7 is surface charge and will quickly go away with even light loads. Note the voltages.

Now, start the engine. If you have the feature, go to high idle (same as you do to warm up the engine after 30 seconds at low idle). Go back and read voltage at the batteries. Both banks should be higher than the last reading and if the batteries are not deeply discharged, between 13.5 and 14.5 VDC. If this is not the case, you will need to troubleshoot your charging/isolation system.

With 120 VAC from shore power or generator, the converter, charger or inverter/charger should also charge the house bank and on many the chassis batteries as well. To verify, disconnect from shore power/generator for several hours. Read voltage at house and chassis batteries. Plug in/turn on generator. Read voltage. Voltage at any battery receiving a charge should go from under 13 VDC to 13.2-14.2 VDC. If it remains the same, that bank is not being charged. Many coaches do not charge the chassis battery from shore power��" a serious problem with all the parasitic loads on today’s chassis battery. IMO, this should be corrected. Xantrex Echo charger, a separate “small smart charger for chassis bank, solar panel, or even wire from house positive to chassis positive all work to keep the chassis battery charged. If using a wire from positive to positive, BOTH ends must have a fuse, since touching any metal or ground terminal with either end would cause a dead short. Do NOT use a wire if one bank is deeply discharged and the other fully charged, as small wires are not designed to handle the rapid transfer of large amounts of current��"this is for maintaining a charge only.

You also have a battery boost/combine switch. This allows the two banks to be combined, with house battery assisting the chassis battery in starting the engine or the chassis battery assisting the house battery in starting the generator. To verify its functioning, disconnect from shore power/generator for several hours. Turn on some 12 VDC loads to slightly discharge the house battery. Read battery voltage at each battery��"all you are really looking for is that they are different. Now, with someone activating the boost switch, verify that both batteries are at exactly the same voltage. If not, you need to troubleshoot and determine if the switch/wiring or solenoid is faulty.

If the battery voltages were not the same with the boost switch activated, locate the combine solenoid. It should be near the batteries and have a large cable going to each battery bank. Recheck voltage from each large lug to ground��"with solenoid working, they should be exactly the same. It will also have either one or two small wires to it. If two, one will be the signal wire and the other a ground. If one small wire, it will be the signal wire from the dash switch, and the solenoid grounds directly from metal to metal contact. With your voltmeter or even a test light, check for 12 VDC/light at the small signal wire lug to ground. If present, but the voltage at the two large lugs is not the same (i.e. batteries not combined), the solenoid is defective. If you did not get 12 VDC/light from the signal terminal with boost switch activated you need to check the dash switch and wiring and you still need to verify that the solenoid is working. With a small wire (will only be carrying less than one amp) go from either large lug to the small signal wire lug (not ground lug). If the solenoid is functioning, you should hear a loud “click†and the two large lugs should read the same voltage.

Wolfe, this was a nic e post. But, being new to motorhoming, I am still confused. I have been having some trouble starting my coach. The chassis battery seems to be running down and not putting out enough juice to turn the motor. I have it on a drip charger through the shore power connection. Some days it start without a problem, then others i have to get a jump. ( i have access to a service truck with a generator). When hooked up to the mobile jump, it starts instantly. Also, I ran it 2 days prior when i filled the LP tanks up,and drove about 9 miles. My chassis battery also starts the generator.

Here are my questions:

1. Does the drip charger charge the chassis battery ?

2. With the Chassis Battery switch off, would there be any type of draw off the chassis battery, to run it down?

3. Could a couple of cold nights have drained the battery

4. Will drip charger eventually replenish the chassis battery, assuming the battery is still good, which i believe it is.

Thanks for any thoughts you may have

[wolfe10]

.

Here are my questions:

1. Does the drip charger charge the chassis battery ?

2. With the Chassis Battery switch off, would there be any type of draw off the chassis battery, to run it down?

3. Could a couple of cold nights have drained the battery

4. Will drip charger eventually replenish the chassis battery, assuming the battery is still good, which i believe it is.

Thanks for any thoughts you may have

1. There are too many ways that converters, chargers or inverter/chargers can be set up to be able to tell you how yours is wired. But with a digital voltmeter (start under $20 at Radio Shack, Sears, etc) you can tell very quickly what is happening on your coach. With shore power on, check voltage at each battery bank. Over 13.0 indicates a battery is being charged.

2. Again, too many ways for these to be wired. Easy answer is to use a 12 VDC ammeter to check for draw with the switch OFF.

3. Shouldn't. But your battery may be bad-- deeply discharging them is REALLY hard on any battery, particularly starting batteries. You should completely charge them and have them load tested (most places that sells batteries will do it for free).

4. You need to tell us what charger you have. "Drip Charger" is not a term I know. Do you have a converter, charger or inverter charger for your house battery charging? Do you have a second charger for the chassis batteries? And yes, a trickle charger, Xantrex Echo charger, etc will keep the chassis battery bank up if working and properly wired.

BTW, be sure to check battery water level. If the plates are exposed, it is another sign that the batteries are on their last legs.

Brett

[joemar1112@yahoo.com]

1. There are too many ways that converters, chargers or inverter/chargers can be set up to be able to tell you how yours is wired. But with a digital voltmeter (start under $20 at Radio Shack, Sears, etc) you can tell very quickly what is happening on your coach. With shore power on, check voltage at each battery bank. Over 13.0 indicates a battery is being charged.

2. Again, too many ways for these to be wired. Easy answer is to use a 12 VDC ammeter to check for draw with the switch OFF.

3. Shouldn't. But your battery may be bad-- deeply discharging them is REALLY hard on any battery, particularly starting batteries. You should completely charge them and have them load tested (most places that sells batteries will do it for free).

4. You need to tell us what charger you have. "Drip Charger" is not a term I know. Do you have a converter, charger or inverter charger for your house battery charging? Do you have a second charger for the chassis batteries? And yes, a trickle charger, Xantrex Echo charger, etc will keep the chassis battery bank up if working and properly wired.

BTW, be sure to check battery water level. If the plates are exposed, it is another sign that the batteries are on their last legs.

Brett

Brett thanks for the input. I call the trickle charger a drip charger. I am pretty certain that the trickle maintains both, chassis and house. As the house batteries are fully charged and the chassis battery seems to be gaining some amps, sinc eyesterday.

I will keep you posted.

Here's another rookie question. Since, my house batteries charge off the engine alternator, is there any reason to run the generator while driving. Wouldn't the engine alternator handle the house batteries as they supply the internal appliances and whatever else is drawing?

[wolfe10]

Brett thanks for the input. I call the trickle charger a drip charger. I am pretty certain that the trickle maintains both, chassis and house. As the house batteries are fully charged and the chassis battery seems to be gaining some amps, sinc eyesterday.

I will keep you posted.

Here's another rookie question. Since, my house batteries charge off the engine alternator, is there any reason to run the generator while driving. Wouldn't the engine alternator handle the house batteries as they supply the internal appliances and whatever else is drawing?

Normally a trickle charger maintains the chassis battery, with the "main" charger, converter or inverter/charger taking care of the house batteries.

And VOLTS are what you measure to determine battery charge (yes, amps can be used, but require monitoring with some higher end equipment such as the Xantrex Link products).

Basically, if battery is 13.2 to 13.5 VDC, they are being charged. Readings up to about 14.2 are OK if the batteries are deeply discharged (bulk mode).

And your alternator should charge BOTH house and chassis batteries while the engine is running-- they always charge the chassis battery, or you could not drive very far without running them down. Again all you need to do is check voltage at both battery banks with engine running. With shore power off and engine running, voltage should be 13.5 VDC to 14.2 VDC.

Brett

[lebjdixon]

Having trouble finding the PN Napa 85-120 Isolator Relay! Did you order it or buy it directly from NAPA, THANKS PEEPAFOX, I think I may need one, cause it's hard finding the White Rodgers, I have a 1998 Holiday Rambler

[dickandlois]

lebjdixon,

Welcome to the forum!

The NAPA part number comes back as a Battery Charger.

I have tried different variations of the number and not found any reference to relays. So I'm going to play with the OEM number to see what comes up.

OK the part is an 80 to 120 Amp rated unit from White Rogers.

This is a link to a solenoid that should handle the current. The thing is they come in so many configurations.

There are different size terminals and some solenoids are internally wired to isolate different wires or the unit itself from ground.

http://www.supplyhouse.com/White-Rodgers-586-105111-Solenoid-SPNO-12-VDC-Isolated-Coil-Normally-Open-Continuous-Contact-Rating-200-Amps-Inrush-600-Amps-14829000-p

Rich.

[carlpeterson]

Brett- thanks for your in depth answer to all technical questions. We all appreciate your answers. Carl Peterson

[liedtkekla]

I have an electrical problem.

I purchased in 2013, a 2014 Thor Tuscany XTE, and since purchased, I had to replace the EMS board four (4) times.

My rear A/C after a specific time, just telling me on the control panel, rear A/C off.

The blower still works, but the compressor is not turning on again.

It is frustrating, as it is a recurring problem.

What can be done to fix it? Or what could be the reason for have to happen that so many times?

ANY help would be appreciated.

Thanks

[dickandlois]

liedtkekla,

Welcome to the FMCA Forum!

Question: do you use shore power most of the time? or run the generator frequently?

Do you turn of your AC units and other loads before connection to shorepower or starting the generator?

If the above questions are a yes then.

The fact that you have had to replace the EMS 4 times, kind of makes me think, bad connections or wiring between the coach and shorepower cables.

Possible loose or corroded connections at the transfer relay / solenoid. Bad ground connections.

Do you have a multimeter to work with?

Rich.

[gbrinck]

The a/c blower is also 120v powered, so if the fan is running you have 120v power and the EMS should not be involved. Fan on but no compressor is often a problem with a failing hard start capacitor and its associated "run" module. At least, that's the first thing I would investigate.

What brand and model is your EMS. Are we talking about the device that sheds loads to keep within a 30A power budget, or some other device. Thanks to some confusing product names from Progressive Industries, the acronym "EMS" is sometimes applied to shore power monitors instead of the load management type of unit, e.g. INtelletec.

[huffypuff]

Since this thread about solenoids came back to life one in my coach died. Well not all the way it still work as a battery boost from the cockpit but not allowing the house batteries to charge while driving. I don't think it like the steady vibration while the engine is running as would not connect the two batteries banks even though it had voltage. I found a solenoid that is named a bear for it is very strong. I replace the bad solenoid with the one nickname bear and it works great. Below is a link to it.

http://shopping.murcal.com/Catalog/Bear-DC-Contactor-Family/114-1211-020

[desertdeals69]

Having trouble finding the PN Napa 85-120 Isolator Relay! Did you order it or buy it directly from NAPA, THANKS PEEPAFOX, I think I may need one, cause it's hard finding the White Rodgers, I have a 1998 Holiday Rambler

I have used the NAPA relay and had it fail. They come with a lifetime warranty so it was replaced. I found another relay which will work on ebay. Look up an electric golf cart relay. Its continuous duty and they sell for about $10. The relay from NAPA is about $45. I carry a golf cart relay so I can use it when the NAPA one fails, until I can find a NAPA store.

[jleamont]

Anyone know what this solenoid is labeled as that has caused so many to become stranded, no starts etc. I carry one as a spare but when I open up my power distribution bay there are several back there. I was thinking battery cutout but not sure.