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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
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  #1  
Old 10-18-2013
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Solar Battery Charging

My boat has two 80 watt solar panels (total 160 watt) that feed a charge controller. This charges the 225 amp hour AGM house battery. That all works fine.

I also have a Costco starting/deep cycle lead acid battery I use to start the engine (this battery is new). The engine alternator will charge this battery.

The house and engine start battery can be connected together via a battery switch. When the engine battery started to go bad, I could start the engine using the switch which would connect the house and start batteries.

Since I have no trickel charger on the engine battery, can I leave the house and engine battery connected to keep a full charge? I understand the charge characteristics between the batteries are different so not sure if this is a no no. I do see that the charge voltage for the house AGM battery is 14 volts or more- this seems high, but all has run well for 6 years so assume all is well.
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Old 10-18-2013
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Re: Solar Battery Charging

Yes, you could do that, but it's not the optimum solution.

AGM and flooded battery charging profiles are almost identical, so no problem there.

However, in the (somewhat unlikely but not impossible) event that a short developed in either battery bank, or a load was inadvertently left on (bilge pump continuous running?) you could flatten both banks.

A better solution is to use a voltage follower device like the Xantrex EchoCharge or the Balmar DuoCharge to keep the starting battery topped off.

These devices work by sensing a charging voltage on the house batteries and, when it is present, drawing off enough current to just top off and maintain the start battery. All automatic. No switches required. You don't have to remember to switch anything.

In your situation, the EchoCharge would be appropriate. It costs about $140 and is very easy to install. Mine has worked 24/7 for the past nine years, and I've installed a bunch of them on client's boats....all without issue so far as I know.

IMHO, these devices are better than "combiners" because there are no mechanical relays to go bad and they allow regulated current to flow in only one direction: from the house batteries to the start battery.

Keep in mind that the typical start battery requires VERY LITTLE CHARGING to keep it topped off. But, flooded LA batteries do need to be kept at a high state of charge to slow the sulfation process.

BTW, both AGM and flooded batteries like to be charged at over 14 VDC. Lifelines like 14.4-14.8VDC, while the Trojan T-105s like 14.6-15.0VDC during the absorption phase. I assume you have a smart controller for those panels?

Bill

Last edited by btrayfors; 10-18-2013 at 05:57 PM.
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Re: Solar Battery Charging

Quote:
Originally Posted by btrayfors View Post
Yes, you could do that, but it's not the optimum solution.

AGM and flooded battery charging profiles are almost identical, so no problem there.

However, in the (somewhat unlikely but not impossible) event that a short developed in either battery bank, or a load was inadvertently left on (bilge pump continuous running?) you could flatten both banks.

A better solution is to use a voltage follower device like the Xantrex EchoCharge or the Balmar DuoCharge to keep the starting battery topped off.

These devices work by sensing a charging voltage on the house batteries and, when it is present, drawing off enough current to just top off and maintain the start battery. All automatic. No switches required. You don't have to remember to switch anything.

In your situation, the EchoCharge would be appropriate. It costs about $140 and is very easy to install. Mine has worked 24/7 for the past nine years, and I've installed a bunch of them on client's boats....all without issue so far as I know.

IMHO, these devices are better than "combiners" because there are no mechanical relays to go bad and they allow regulated current to flow in only one direction: from the house batteries to the start battery.

Keep in mind that the typical start battery requires VERY LITTLE CHARGING to keep it topped off. But, flooded LA batteries do need to be kept at a high state of charge to slow the sulfation process.

BTW, both AGM and flooded batteries like to be charged at over 14 VDC. Lifelines like 14.4-14.8VDC, while the Trojan T-105s like 14.6-15.0VDC during the absorption phase. I assume you have a smart controller for those panels?

Bill
Aloha and thanks for that great information.

Yes the AGM battery is charged by a Xantrex C series charger. It seems to work well, but is not water proof. So far no water damage. The charger does not have the battery temperature monitor included, I could easily add it if needed.
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Re: Solar Battery Charging

Another thought,
What about installing say a 20 watt solar panel and just connect directly to the engine start battery to keep topped up (no charge controller). Would that be ok?
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Old 10-18-2013
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Re: Solar Battery Charging

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Originally Posted by casey1999 View Post
Another thought,
What about installing say a 20 watt solar panel and just connect directly to the engine start battery to keep topped up (no charge controller). Would that be ok?
No. you need a controller. The battery voltage without one will be too high.

I like Bill's Echo Charge solution, I install many as well without problems. Ideally I would change the alternator output to the house bank - and any other charge sources as well. That way all batteries will be fully charged automatically.
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