Solar bat charging

[Ramona]

Because of battery draw down while parked w/out shorepower, I purchased a Renogy 100w Solar suitcase w/Voyager controller. Hooked it up to the just the house batteries (2 in parallel) and was literally stunned how well it worked—it even charged the engine battery (some kind of transfer switch enabled this?). Charge was brought up from 12.4v to about 14v in 2 hours.

But because of where the solar panels have to be located, the system dosen't get enough sun to go through it's entire cycle—bulk, boost, float—during the day (not sure that matters).
Anyway, the solar charger keeps both the house and chassis at the same voltage. I can't check it at night, but I think that they are getting back down to 12.3 or so every night before being brought back up to over 13v everyday.
I know that the deep cycle house batteries are meant to charge, de-charge, etc., many times.
Here's the question: Does this same charging, de-charging, and re-charging everyday while parked harm the engine battery? If yes, how do I avoid charging the engine bats while trying to charge the house batts?
Thanks.

[Holiday1]

Doesn't your house batteries and engine batteries have individual disconnect switches

[Ramona]

Originally Posted by Holiday1

Doesn't your house batteries and engine batteries have individual disconnect switches

Nope. Only House disconnect and it is disconnected while charging—if not, even the 100w solar charger dosen't keep up, at least not where solar is currently located.

[Crasher]

I find it hard to believe that a 100 watt panel with recharge two house batteries and the chassis battery during the day. It will only put our 6 amp/hour at the peak sun exposure. Generally about 30 -35 amps per day. It just doesn't compute unless you are not using any 12 volt power.

[twinboat]

If they are dropping to 12.3 volts every night, either to much stuff in on or the batteries are bad. Batteries should hold 12.6 volts for a few days.

It is using up capacity in any battery, dropping and recharging every night, even deep cycle.

If you can get to the unit every day, leave the solar off one night and check the voltage in the morning. The batteries will drop to 12.6 volts, that normal resting volts.

If they are dropping more the that, see what's on.

[Ramona]

Originally Posted by Crasher

I find it hard to believe that a 100 watt panel with recharge two house batteries and the chassis battery during the day. It will only put our 6 amp/hour at the peak sun exposure. Generally about 30 -35 amps per day. It just doesn't compute unless you are not using any 12 volt power.

I said I was stunned. And it did it in just a few hours. (GOOD sun in ABQ) And I am using 12v power otherwise i wouldn't need the solar panels at all

[Ramona]

Originally Posted by twinboat

If they are dropping to 12.3 volts every night, either to much stuff in on or the batteries are bad. Batteries should hold 12.6 volts for a few days.

It is using up capacity in any battery, dropping and recharging every night, even deep cycle.

If you can get to the unit every day, leave the solar off one night and check the voltage in the morning. The batteries will drop to 12.6 volts, that normal resting volts.

If they are dropping more the that, see what's on.

Agreed. Wondering if bats are bad (on brand new coach). We have turned everything off that we can. Before solar, Engine batt was holding about 12.5 for 2-3 days, but House down to 12.2 after 4 days. Spoke to our dealer and Newmar "expert" and both said that this was "normal" or even "good" (in other words less draw down than expected).

So you are saying this way of charging is bad for BOTH house and engine batts?

[oscarvan]

OK, some misconceptions here.... a lead acid battery that is FULLY charged and then at rest for an hour or so will be 12.6V NEVER MORE. It's the laws of chemistry and physics.

What you are seeing is a charge voltage.

When you disconnect the charger and let the battery settle down and then it reads 12.3 it means that it's about 70% charged. 12.1 is about 50%

So.... you're not really getting them fully charged which is why they settle down at less than 12.6

Also, at rest means NO LOAD. Any kind of load will lower the voltage.

Still, you're doing pretty good. As long as you don't discharge them past 50% (12.1-12.2) you're not hurting them.

If you truly want to play the solar boon docking game by the numbers you need a battery condition monitor. You can control what you can measure. This one is IMO the best deal out there....

https://www.amazon.com/victron-batte...attery+monitor

By means of a "shunt" (google that) it measures amps flowing in or out. You fully charge the battery and set it to 100% Now as you charge/discharge you will keep a real time count of what goes in and out and it will calculate the SOC (state of charge) continuously.

[wingnut60]

There are a limited number of charge/discharge cycles in any battery. Every time you discharge it to any extent and recharge it, there is a reduction in total life expectancy. Somehow, don't think you are getting a real charge to the higher voltage you mention, and need to check only the 'at rest' voltage. Or, get a battery monitor that will give you the actual SOC--State of Charge. Victron makes several good ones.

[Ramona]

Originally Posted by oscarvan

OK, some misconceptions here.... a lead acid battery that is FULLY charged and then at rest for an hour or so will be 12.6V NEVER MORE. It's the laws of chemistry and physics.

What you are seeing is a charge voltage.

When you disconnect the charger and let the battery settle down and the it reads 12.3 it means that it's about 70% charged. 12.1 is about 50%

So.... you're not really getting them fully charged which is why they settle down at less than 12.6

Still, you're doing pretty good. As long as you don't discharge the past 50% (12.1-12.2) you're not hurting them.

Oh yes, I understand that that 13.x or 14.x is the charging voltage and that once the charger goes into Float mode, it'll drop to 12.7 or 12.6.
Was just wondering if all that up and down was bad for the Engine batt.
You say no, as long as above 12.1 or 12.2 . I like that answer.

Just have to go with it at some point and see what happens.
Thanks oscarvan

[Crasher]

What oscarvan said. When I have our coach parked without shore power, the voltage will read 13.3 volts while solar charging, but 2-3 hours after the charging stops it will settle to 12.7 volts or 100% SOC. I have everything turn off, so in the morning it is still at 12.7 volts with 900 amps of storage and 620 watts of solar. With two house batteries, you are probable close to 225 amps of storage capacity. If they were @ 50% or 12.1 volts with no load, then a 100 watt solar panel could add 35 amps on a good day. That would get the batteries up to about 65%. If your capacity is 225 amps, then a 100 watt solar panel can replace 15% of the used capacity. All measurements need to be taken after the batteries have set for a couple hours after use or charge.

[twinboat]

Cycling the start battery, is going to use it up, and wear it out in less then a year.

Every time you discharge and recharge any battery it loses some life.
Deep cycle batteries have about 1000, 50% cycles in them.

Start batteries have less then 100, 50% deep cycles in them.

[oscarvan]

Originally Posted by Ramona

Was just wondering if all that up and down was bad for the Engine batt.

"Bad" is a relative term. It won't like it as much as a deep cycle battery. But it won't send it off the cliff in a few months either.

I've played the game with starting batteries that lasted several years.

[Ramona]

Originally Posted by wingnut60

There are a limited number of charge/discharge cycles in any battery. Every time you discharge it to any extent and recharge it, there is a reduction in total life expectancy. Somehow, don't think you are getting a real charge to the higher voltage you mention, and need to check only the 'at rest' voltage. Or, get a battery monitor that will give you the actual SOC--State of Charge. Victron makes several good ones.

Good info. Thanks wingnut60