Solar panel for engine battery charging?

[PetiteFleur]

I've the old fashioned 1, both 2 battery switch with two batteries which I alternate on a daily basis. Had to buy a new battery last week when in Limehouse basin (Thanks to battery megastore who delivered the next day!). So was thinking on the way home whether to fit a dedicated starter battery(25hp Beta) which is only charged from a solar panel, say a 30 or 50 w panel. What are the disadvantages and has anyone done it?

 

[PaulRainbow]

I've the old fashioned 1, both 2 battery switch with two batteries which I alternate on a daily basis. Had to buy a new battery last week when in Limehouse basin (Thanks to battery megastore who delivered the next day!). So was thinking on the way home whether to fit a dedicated starter battery(25hp Beta) which is only charged from a solar panel, say a 30 or 50 w panel. What are the disadvantages and has anyone done it?

Would be unusual to only charge it from a solar panel. Better bet would be to fit the dedicated battery and to charge it via a split charge device. If you fitted a VSR you could connect a solar panel to the domestic batteries and it would keep them all nicely topped up whilst you were away from the boat, plus add a little power whilst you were onboard.

 

[VicS]

I've the old fashioned 1, both 2 battery switch with two batteries which I alternate on a daily basis. Had to buy a new battery last week when in Limehouse basin (Thanks to battery megastore who delivered the next day!). So was thinking on the way home whether to fit a dedicated starter battery(25hp Beta) which is only charged from a solar panel, say a 30 or 50 w panel. What are the disadvantages and has anyone done it?

As PR says it would be unusual to charge an engine start battery only from a solar panel ...

If you have space for an additional battery and wish to keep the old 1, 2, both selsctor switch the simplest way forward is to parallel the existing two batteries and connect to terminal 2 of the switch. These will form your house battery bank

Connect your new engine start battery , which need be no larger than Beta recommend, to terminal 1.

Fit your solar system with a dual output PWM regulator connected directly to the two battery banks. Or a single output regulator connected to the house battery bank with a VSR / ACR linking in the engine start battery.

Use your 1,2,both switch as follows

When you want to start the engine select battery 1.
Start the engine
Allow the engine start battery to recharge ( a voltmeter and or an ammeter will be a useful guide) then switch briefly to both then to battery 2.

Keep battery 2 in service until you next need to start the engine. ( Or switching everything off when leaving the boat)

DO NOT switch via OFF if the engine is running!​

Only the skipper is allowed to operate the battery selector switch.

If you need to start the engine in a hurry don't mess about switching from domestic battery to engine start battery, just use the domestic bank.

 

[Glenlivet]

Easiest to fit one of these with a VSR (voltage sensitive relay). Solar panel to house batteries through an MPPT controller, house and engine batteries then separated on load but solar/engine charging both and the ability to combine if necessary.
https://www.bluesea.com/products/6011/m-Series_Mini_Dual_Circuit_Plus_Battery_Switch_-_Red

 

[PaulRainbow]

Easiest to fit one of these with a VSR (voltage sensitive relay). Solar panel to house batteries through an MPPT controller, house and engine batteries then separated on load but solar/engine charging both and the ability to combine if necessary.
https://www.bluesea.com/products/6011/m-Series_Mini_Dual_Circuit_Plus_Battery_Switch_-_Red

That's a reasonable arrangement, but it should be noted that if you suffer certain types of battery failure you cannot use the combine feature without first disconnecting the faulty battery.

Best bet is three separate switches, one for each bank and one for emergencies, with the emergency switch connected to the load terminals of the main isolators. This allows the faulty battery to be isolated, then use the emergency switch.

Split charging can be done by a variety of methods, depending on various factors.

 

[MAURICE]

Ive done just that with a 5 watt panel. My set up is 240 watt panel for my domestic battery bank which i have 3 180 A/H batteries and a 100 A/H starter battery My boat is in the med so a lot more brighter days. It was cheaper and easier than the other options. The other thing you may consider is a solar panel controller with outputs for two battery banks.
Maurice

 

[William_H]

Solar panel should be chosen on the basis of what size you can reasonably mount. Larger the better.
VSRs are not always so successful with a small solar panel as while they provide a nice little trickle charge to a battery they do not always raise the voltage enough to activate the VSR. Better is a solar controller with dual output. Or for a smaller solar panel (10w) do not have a controller but fit 2 diodes to direct current to 2 batteries independently with switch off.
ol'will

 

[Topcat47]

+1 for separate isolation switches. I have two small "Maplin" panels which I connect inside my south facing saloon window, one for each battery (I have two). They manage to top up/maintain voltage both batteries even in the depths of winter, if I keep Snark Afloat. Now Maplin's gone I'd look to e-bay for replacements.

 

[vyv_cox]

As VicS says, I have had a dual bank PWM charger by SunWorks for many years. One of these https://sunworks.co.uk/product-category/solar-charge-controllers/dual-battery-charge-controller/ although mine is only 9 amps. Has always worked perfectly, keeps the starter battery voltage up even though we rarely switch to it.

 

[VicS]

I've the old fashioned 1, both 2 battery switch with two batteries which I alternate on a daily basis. Had to buy a new battery last week when in Limehouse basin (Thanks to battery megastore who delivered the next day!). So was thinking on the way home whether to fit a dedicated starter battery(25hp Beta) which is only charged from a solar panel, say a 30 or 50 w panel. What are the disadvantages and has anyone done it?

Vyv's post reminds me of another way of managing a two bank battery system without a change to multiple switches, but which lends itself to use with a 1,2, both switch.

Wire the batteries as I suggested in #3 with the two original batteries connected in parallel to one terminal of the switch and the new battery to the other.

Fit a VSR and your solar panel with a dual output controller to both banks . ( or with a single output controller to just the two battery bank , allowing the VSR to keep the other battery charged from both solar and engine.)

Dub the two battery bank the "main" battery and the single battery the "emergency start" battery.

Use the "main" battery bank for all purposes, including engine starting.

Switch to the "emergency start battery" only if/when necessary or to occasionally test it

This is basically the system preferred in N America and is I believe described in Calder's book.

 

[PetiteFleur]

Thanks for all the answers, it's given me food for thought. I've spoken to Photonic Universe who supplied a 50w panel and a dual battery controller which I fitted before my trip. They suggested I have a separate engine battery and parallel the two existing batteries as a domestic bank, and with the dual battery controller, one output to the engine battery, say 30% and 70% to the domestic bank. I have room for another 30w panel making 80w in total. If the engine battery is fully charged, all the output goes to the domestic bank. I also have room for 2 x 20w panels if the 80w is insufficient. As I've fitted one new domestic battery, I will probably fit another new one so they are of the same age.
Beta recommend a 70ah battery of cc450 capacity but I only have room for a smaller capacity of 60ah and 480cc which I suspect will be fine as the engine always starts immediately. My VW Touran was twice the size and I replaced that battery in February this year and that lasted 10 yrs!

 

[VicS]

Thanks for all the answers, it's given me food for thought. I've spoken to Photonic Universe who supplied a 50w panel and a dual battery controller which I fitted before my trip. They suggested I have a separate engine battery and parallel the two existing batteries as a domestic bank, and with the dual battery controller, one output to the engine battery, say 30% and 70% to the domestic bank. I have room for another 30w panel making 80w in total. If the engine battery is fully charged, all the output goes to the domestic bank. I also have room for 2 x 20w panels if the 80w is insufficient. As I've fitted one new domestic battery, I will probably fit another new one so they are of the same age.
Beta recommend a 70ah battery of cc450 capacity but I only have room for a smaller capacity of 60ah and 480cc which I suspect will be fine as the engine always starts immediately. My VW Touran was twice the size and I replaced that battery in February this year and that lasted 10 yrs!

It's the CCA that matters for a starting battery . The Ah capacity is of little relevance if the CCA is adequate

If space is tight you could consider a Red Flash 1100 which has a CCA of 500, but a capacity of only 43 Ah, and measures only 250 x 97 x 206 high and also being an AGM battery can be laid on its side.

http://www.dmstech.co.uk/downloads/DMS_data_redflash_highrate_web.pdf