This topic has been covered many times over the years but in my opinion, technology, prices, knowledge, and parts availability changes frequently so it's worth a revisit.
Fast forward through a Michigan winter and here I am again trying to figure out an additional way to charge our 470Ah (4x GC2) lead acid house bank so we aren't tied to being plugged in at a marina every night.
Currently the original 51A alternator charges the dedicated group 27 engine battery only. The battery charger charges the house bank when on shore power. There is a combiner switch that will connect the engine battery and house bank but I've never attempted to use it. Last summer I installed much-needed fusing and purchased and installed an ACR but after reading multiple posts about frying original alternators charging the 4x golf cart banks like mine, I didn't make the final ACR connections.
We mostly day sail but we would like to take a two week trip go "up north" as we say in Michigan. It's usually difficult to get last-minute transient slip reservations to work around weather and lake conditions so having the ability to anchor for as much as three nights is a must.
Based on my extensive 72-hour energy budget spreadsheet, I estimate 120-150Ah use in a 24 hour period with the fridge mostly empty. With our family of five, the fridge will be completely full so there's a possibility my estimate could be low. (My estimate comes from watching trends on my cheap $20 voltmeter/watt counter and shunt combo from Amazon.) That puts us at 50% SOC sometime during the second night, assuming our batteries are actually relatively healthy. To get amps back in the bank, I see four options:
1. Utilize existing alternator but closely monitor SOC to stay above an unknown threshold that the alternator can handle.
2. Upgrade alternator to 90A or 105A with external smart regulator.
3. Add 2x 200W rigid solar panels on a frame above the bimini. I figure this is about the maximum I could reasonably add.
4. Bring our 3500W generator along. It's noisy, smelly and I don't know where we'd put it or the gasoline but we'd have battery charging, air conditioning, and the kids would have TV.
With options 1, 2, or 3, the big unknown for me is the math of the charging sequence for deep cycle batteries. This is especially true with the solar option where the available amps varies by time of day. I've read (a few times) the thread about battery acceptance but I'm still not clear on the math behind it. Google wasn't much help either. There's lots of information out there about discharging but not much on what's actually happening in the three charging states and what the ideals are.
Reference screenshots of the spreadsheet show two days based on leaving the dock in the morning on day 1 100% charged. One column shows estimated available amp hours without solar and one shows estimated available amp hours with solar and 80% charging efficiency.
Here's an excellent thread on alternators for this type of house bank: https://c34.org/bbs/index.php/topic,9773.0.html
Fast forward through a Michigan winter and here I am again trying to figure out an additional way to charge our 470Ah (4x GC2) lead acid house bank so we aren't tied to being plugged in at a marina every night.
Currently the original 51A alternator charges the dedicated group 27 engine battery only. The battery charger charges the house bank when on shore power. There is a combiner switch that will connect the engine battery and house bank but I've never attempted to use it. Last summer I installed much-needed fusing and purchased and installed an ACR but after reading multiple posts about frying original alternators charging the 4x golf cart banks like mine, I didn't make the final ACR connections.
We mostly day sail but we would like to take a two week trip go "up north" as we say in Michigan. It's usually difficult to get last-minute transient slip reservations to work around weather and lake conditions so having the ability to anchor for as much as three nights is a must.
Based on my extensive 72-hour energy budget spreadsheet, I estimate 120-150Ah use in a 24 hour period with the fridge mostly empty. With our family of five, the fridge will be completely full so there's a possibility my estimate could be low. (My estimate comes from watching trends on my cheap $20 voltmeter/watt counter and shunt combo from Amazon.) That puts us at 50% SOC sometime during the second night, assuming our batteries are actually relatively healthy. To get amps back in the bank, I see four options:
1. Utilize existing alternator but closely monitor SOC to stay above an unknown threshold that the alternator can handle.
2. Upgrade alternator to 90A or 105A with external smart regulator.
3. Add 2x 200W rigid solar panels on a frame above the bimini. I figure this is about the maximum I could reasonably add.
4. Bring our 3500W generator along. It's noisy, smelly and I don't know where we'd put it or the gasoline but we'd have battery charging, air conditioning, and the kids would have TV.
With options 1, 2, or 3, the big unknown for me is the math of the charging sequence for deep cycle batteries. This is especially true with the solar option where the available amps varies by time of day. I've read (a few times) the thread about battery acceptance but I'm still not clear on the math behind it. Google wasn't much help either. There's lots of information out there about discharging but not much on what's actually happening in the three charging states and what the ideals are.
Reference screenshots of the spreadsheet show two days based on leaving the dock in the morning on day 1 100% charged. One column shows estimated available amp hours without solar and one shows estimated available amp hours with solar and 80% charging efficiency.
Here's an excellent thread on alternators for this type of house bank: https://c34.org/bbs/index.php/topic,9773.0.html