Jumper from house batteries to chassis batteries?

[BeltoneMagoo]

Have used a 5 amp Trik-L-Start with good results but wanted a little more to replace the original 15 amp factory unit I had. Trik-L-Start now makes a 15 amp unit and that is what I changed to earlier this year. Very happy with their units. Try Ultra TRIK-L-START Starting Battery Charger/Maintainer to have a look. They are really simple to install.
Good luck and safe travels!

[dieseldale1]

I like the idea of a diode. Your chassis battery would stay charged and never drain with the house batteries. What amp load of diode, wire size, and would it not be good to put an overload relay in series with the diode?

[Old Bounder]

Originally Posted by dieseldale1

I like the idea of a diode. Your chassis battery would stay charged and never drain with the house batteries. What amp load of diode, wire size, and would it not be good to put an overload relay in series with the diode?

A simple diode isolator like this would do the job nicely. We're not talking recharging a dead battery here, 8 or 10 gauge wire would be more than sufficient for a maintenance charge.

[3rd stage]

Originally Posted by loulong

A simple diode isolator like this would do the job nicely. We're not talking recharging a dead battery here, 8 or 10 gauge wire would be more than sufficient for a maintenance charge.

Just be aware that these diodes typically have about a 0.7V forward voltage drop across them. That is, the voltage out of the isolator will be approx 0.7V lower than the input voltage.
What this means is that if your float voltage on the house batteries is set to, say, 13.2V, the voltage presented to the chassis batts through the isloator will be on the order of 12.5V. Last I knew 12.5V is not enough to keep flooded wet cells charged.
It's better to let the Inverter/Charger charge the house batts and add a separate Battery Maintainer (charger) to keep the chassis batts full.
HTH.
Andy

[Old Bounder]

Originally Posted by 3rd stage

Just be aware that these diodes typically have about a 0.7V forward voltage drop across them. That is, the voltage out of the isolator will be approx 0.7V lower than the input voltage.
What this means is that if your float voltage on the house batteries is set to, say, 13.2V, the voltage presented to the chassis batts through the isloator will be on the order of 12.5V. Last I knew 12.5V is not enough to keep flooded wet cells charged.
It's better to let the Inverter/Charger charge the house batts and add a separate Battery Maintainer (charger) to keep the chassis batts full.
HTH.
Andy

It seems to me the chassis battery could not drop below the 12.5 volts. How is this not going to keep the chassis battery charged at least to that level. I would certainly rather find my chassis battery at 12.5v, after two months, than find it dead.

By the way - this is exactly how many high end Monaco's are wired.

[Dr4Film]

Originally Posted by BeltoneMagoo

Have used a 5 amp Trik-L-Start with good results but wanted a little more to replace the original 15 amp factory unit I had. Trik-L-Start now makes a 15 amp unit and that is what I changed to earlier this year. Very happy with their units. Try Ultra TRIK-L-START Starting Battery Charger/Maintainer to have a look. They are really simple to install.
Good luck and safe travels!

This is their 15 amp charger. It's called the Amp-L-Start.

AMP-L-START Starting Battery Charger/Maintainer - Overview Page

The one that your link goes to is the 5 amp unit.

Dr4Film ----- Richard

[94-Newmar]

Originally Posted by Cusn Edy

Our motorhome is going into storage for the winter this weekend and I started to wonder something. Can I place jumper wires between the house battery bank and the chassis battery bank so that the chassis batteries would be maintained by the onboard charger rather than running a second battery tender on the chassis batteries? The coach is plugged in but not in a heated storage area. This seems logical and shouldn't be too much load for the inverter/charger as there would only be a total of five batteries. I don't see how this would be any different than having five house batteries. Any thoughts or insights would be very much appreciated.

Matt

Matt, simple solution. I have installed countless numbers of these, even have one in my rig:Sure Power 1315-200 Battery Separator
Hook one side to your house batteries, the other to the chassis batteries - no other wiring is necessary. It automatically connects the sides together when it senses a charge from either side (voltage over 13.2) and automatically disconnects the two sides if either side drops below 12.6vdc. No tuning, no muss, no fuss, install and forget it. $100.00 or so.

[3rd stage]

Originally Posted by loulong

It seems to me the chassis battery could not drop below the 12.5 volts. How is this not going to keep the chassis battery charged at least to that level. I would certainly rather find my chassis battery at 12.5v, after two months, than find it dead.

By the way - this is exactly how many high end Monaco's are wired.

Not to put too fine a point on it, but a reading of 12.5V does NOT indicate a charged battery. Look at this site for some elementary discussion of charging voltages:

How to charge sealed lead acid batteries for engineers.

I quote from the site:
"Minimum voltage
Anything above 2.15 volts per cell will charge a lead acid battery, this is the voltage of the basic chemistry. This also means than nothing below 2.15 volts per cell will do any charging (12.9V for a 12V battery) However, most of the time a higher voltage is used because it forces the charging reaction at a higher rate. Charging at the miminum voltage will take a long long time. As you increase the voltage to get faster charging, the voltage to avoid is the gassing voltage, which limits how high the voltage can go before undesirable chemical reactions take place. The typical charging voltage is between 2.15 volts per cell (12.9 volts for a 6 cell battery) and 2.35 volts per cell (14.1 volts for a 6 cell battery). These voltages are appropriate to apply to a fully charged battery without overcharging or damage....snip.....Some lead acid batteries are used in a standby condition in which they are rarely cycled, but kept constantly on charge. These batteries can be very long lived if they are charged at a float voltage of 2.25 to 2.3 volts/cell (at 25 degrees C) (13.5V to 13.8V for a 12V battery). " end quote.

Keeping your batteries at 12.5V will significantly shorten their lives. Just because some mfgrs wire this way does not make it right.

Of course, as always, YMMV.

Andy

[Old Bounder]

Originally Posted by 3rd stage

Not to put too fine a point on it, but a reading of 12.5V does NOT indicate a charged battery. Look at this site for some elementary discussion of charging voltages:

How to charge sealed lead acid batteries for engineers.

I quote from the site:
"Minimum voltage
Anything above 2.15 volts per cell will charge a lead acid battery, this is the voltage of the basic chemistry. This also means than nothing below 2.15 volts per cell will do any charging (12.9V for a 12V battery) However, most of the time a higher voltage is used because it forces the charging reaction at a higher rate. Charging at the miminum voltage will take a long long time. As you increase the voltage to get faster charging, the voltage to avoid is the gassing voltage, which limits how high the voltage can go before undesirable chemical reactions take place. The typical charging voltage is between 2.15 volts per cell (12.9 volts for a 6 cell battery) and 2.35 volts per cell (14.1 volts for a 6 cell battery). These voltages are appropriate to apply to a fully charged battery without overcharging or damage....snip.....Some lead acid batteries are used in a standby condition in which they are rarely cycled, but kept constantly on charge. These batteries can be very long lived if they are charged at a float voltage of 2.25 to 2.3 volts/cell (at 25 degrees C) (13.5V to 13.8V for a 12V battery). " end quote.

Keeping your batteries at 12.5V will significantly shorten their lives. Just because some mfgrs wire this way does not make it right.

Of course, as always, YMMV.Andy

I repeat, the OP didn't ask for the optimum method of CHARGING his chassis batteries. He is investigating ideas to keep them from discharging during storage.

Common sense says holding a battery at 12.5vdc is better than letting it discharge further.

If you think that 12.5V won't eventually charge a battery from <12.5, up to 12.5, then you don't understand the subject.

The diode isolator (with a <12.9v output) is infinitely more desirable than a jumper that will allow all batteries to discharge during a power outage.

Total isolation and/or any of the trickle chargers is the better idea, but that's not what the OP asked about.

[Dr4Film]

My older 2001 Xantrex/Trace Inverter/Converter/Charger is a 2000 Watt model RV2012.

There are three stages of charge which are Bulk, Absorption and Float.

From my experience with the Trace and my four GC2 6 VDC House Batteries & one 8D Chassis Battery, they will bulk charge at about 14.3- 14.4 VDC. The next stage, absorption is about 13.8 - 14.1 VDC and the last stage, float, is generally around 13.5 - 13.7 VDC.

If a charger is Floating at 12.7 I would say it's not working.

Dr4Film ----- Richard

[Dunner]

Originally Posted by loulong

I repeat, the OP didn't ask for the optimum method of CHARGING his chassis batteries. He is investigating ideas to keep them from discharging during storage.

Although it is off-topic from what the OP posted, I find in informative and I'm sure others do too. Threads do tend to wander, but when they stay on the general subject, I find no harm is done. You don't have to read it.

[Old Bounder]

Originally Posted by Dr4Film

If a charger is Floating at 12.7 I would say it's not working.
Dr4Film ----- Richard

You are correct, however, the discussion was about the resultant voltage drop through a diode isolator (typically .7V). This could deliver approx. 12.5V from a float voltage of 13.2V. Not an optimum situation, but it would happen.

[Old Bounder]

Originally Posted by Dunner

Although it is off-topic from what the OP posted, I find in informative and I'm sure others do too. Threads do tend to wander, but when they stay on the general subject, I find no harm is done. You don't have to read it.

Don't get too excited there, Dunner. I wasn't disputing the logic of perfection, but simply explaining that my suggestion, while not necessarily my first recommendation, is an acceptable alternative.

I agree that the more suggestions a person can get, the better.

[3rd stage]

Originally Posted by loulong

I repeat, the OP didn't ask for the optimum method of CHARGING his chassis batteries. He is investigating ideas to keep them from discharging during storage.

Common sense says holding a battery at 12.5vdc is better than letting it discharge further.

If you think that 12.5V won't eventually charge a battery from <12.5, up to 12.5, then you don't understand the subject.

The diode isolator (with a <12.9v output) is infinitely more desirable than a jumper that will allow all batteries to discharge during a power outage.

Total isolation and/or any of the trickle chargers is the better idea, but that's not what the OP asked about.

No need to jump on my air hose Mr. loulong. I was responding to the suggestion that proposed putting a diode in between the batteries resulting in the downstream battery being held at about 12.5 volts (not 12.9 as you stated). This will result in severely shortening the battery life by about 30% due to sulphating. If that's OK, go for it.
As I said, YMMV. I offered this info originally to help clarify some mis-conceptions about diodes in charging circuits, not to upset anyone.

Outta here!
Andy