I replaced the alternator and the replacement came with a charge sensing wire to connect to the positive side of the battery. I would like to add a battery charger to the boat and have been reading about frying to diodes. I also read about using a combiner over an isolator. One person said to connect a on/off switch to the charge sensing wire so to disconnect the circuit while charging the battery. I was hoping that anyone mayhave a detailed "how to" on this as I don't want to blow the alternator!!
Connecting a battery Charger to 1977 Hunter 27 with Yanmar 2qm15
- Thread starter sailermania
- Start date
We really need to know more about the specific devices, especially the brand, size, and model of the alternator and the charger. Also important is what type of batteries you have.
The battery sensing wire is used by the regulator in the alternator to adjust the field current on the alternator so that the battery is not over charged. There is no need to disconnect or put a switch on that wire and it will have no effect on the battery charger.
The battery sensing wire is used by the regulator in the alternator to adjust the field current on the alternator so that the battery is not over charged. There is no need to disconnect or put a switch on that wire and it will have no effect on the battery charger.
There’s generally no risk in having multiple charging sources. The alternator will see the battery being charged and just think it’s a *really* charged battery. The alternator will reduce its field current to just keep the voltage at its set point. Two or more charge sources can usually work together to just push extra current into the bank, especially when it’s at a low state of charge.
Alternators get blown out when their load drops too suddenly. If the load drops faster than the sense wire can reduce the field current then the voltage inside the coil spikes and the diodes can blow out. Having a second charge source usually doesn’t cause that.
The alternator output carries a large current and therefore may have a notable voltage drop along its cable length. By connecting the sense wire directly to the battery post the alternator is able to read the actual battery voltage and modulate its output to keep the voltage exactly at the set point, rather than feeding the bank a lower voltage than it thinks it is.
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,804
Hi. You use the terms
Here is a helpful link. It also has video discussions about charging multiple batteries.
Just to clarify:
- How many batteries are being used to provide power on the boat?
- You want to add a charger. Do you plug your boat into AC power at a dock?
- Combiner’s and Isolator’s of different things. What have you been reading about them that cause you to want to choose one over the other?
Here is a helpful link. It also has video discussions about charging multiple batteries.
On Diana I have a shore-power battery charger (Pro Mariner 12/2) and a 200a solar panel with a Blue Sky controller. I have (at present) no alternator. Both these were installed with OCD-level forethought and attention to detail. One battery starts the engine. The other two are wired as one 12VDC bank for the ‘house’. Both banks are charged (sometimes simultaneously) by both sources. Each bank has its own ‘on-off’ switch. They share chargers but there’s no way to combine them (for loads) directly. The batteries are 3-4 years old now and are always topped off at 13.6-14.4 VDC. No problem at all.
The general rule is to never combine batteries for charging or discharging unless they are the same size, same age, and same type. Most combiners and isolators these days resolve the ‘same type’ part because motorboat mentality states that one must preserve the ‘house’ battery as an emergency backup in the event of primary-battery failure (or, more likely, depletion, because of the accessories they connect to the starting bank). The ‘1-both-2-off’ switch has been the bane of battery health since the 1960s. If you have one, I strongly recommend requiring to be rid of it.
I have pics and explanation on my site - dianaofburlington.com.
‘Simplify, simplify, simplify. Then add lightness.’ - Colin Chapman (Lotus Cars)
The general rule is to never combine batteries for charging or discharging unless they are the same size, same age, and same type. Most combiners and isolators these days resolve the ‘same type’ part because motorboat mentality states that one must preserve the ‘house’ battery as an emergency backup in the event of primary-battery failure (or, more likely, depletion, because of the accessories they connect to the starting bank). The ‘1-both-2-off’ switch has been the bane of battery health since the 1960s. If you have one, I strongly recommend requiring to be rid of it.
I have pics and explanation on my site - dianaofburlington.com.
‘Simplify, simplify, simplify. Then add lightness.’ - Colin Chapman (Lotus Cars)
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When designing critical systems on a boat, redundancy is important. Having the start battery serve as a reserve battery for critical systems is good electrical design.
There are failure modes beyond the poor battery management practices that you cite. Simple equipment like switches and connectors can fail at most inopportune times, leaving the boat without navigation or communication capability. This level of redundancy and safety is required on commercial vessels inspected by the USCG.
A simple solution is the Blue Seas CP+ switch. This is allows 2 separate circuits to be controlled by one switch and in an emergency the 2 circuits can be paralleled. One note of caution, early models of this switch had a design flaw which would allow them to literally fall about without notice rendering them in operable.
There are failure modes beyond the poor battery management practices that you cite. Simple equipment like switches and connectors can fail at most inopportune times, leaving the boat without navigation or communication capability. This level of redundancy and safety is required on commercial vessels inspected by the USCG.
A simple solution is the Blue Seas CP+ switch. This is allows 2 separate circuits to be controlled by one switch and in an emergency the 2 circuits can be paralleled. One note of caution, early models of this switch had a design flaw which would allow them to literally fall about without notice rendering them in operable.
Thank You all for your posts. I apologize as I was away. This Hunter 27 has nothing on it electronically except for a VHF Radio. To summarize some of the comments:
1. First I accidentally connected a battery backwards (it was dark out and I was stupid) and it fried the diodes instantly! I replaced the alternator and it came with the sensing wire.
2. The boat needs new circuit panels as the previous owner chopped them up so I plan on putting in new ac/dc panels.
3. I would like to add the battery charger so when I am at a dock I can have shore power and charge batteries when needed.
4. I did actually just buy a regular battery switch since the existing one is no good either. A regular 1 2 both off switch.
5. lastly my main concern was not frying the diodes again and the sensing wire affecting the diodes if switching the power on and off.
I will have to look at the invoice for the alternator I bought. I know it was a replacement for the Hitachi and is 35 amps.
1. First I accidentally connected a battery backwards (it was dark out and I was stupid) and it fried the diodes instantly! I replaced the alternator and it came with the sensing wire.
2. The boat needs new circuit panels as the previous owner chopped them up so I plan on putting in new ac/dc panels.
3. I would like to add the battery charger so when I am at a dock I can have shore power and charge batteries when needed.
4. I did actually just buy a regular battery switch since the existing one is no good either. A regular 1 2 both off switch.
5. lastly my main concern was not frying the diodes again and the sensing wire affecting the diodes if switching the power on and off.
I will have to look at the invoice for the alternator I bought. I know it was a replacement for the Hitachi and is 35 amps.
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,804
It is smart to do a power worksheet identifying the amount of amp hours you will consume each day. This gives you a measure of how much battery storage you need. That number gives you the amount of generation power you need. If you have a 100 amp hour FLA battery you should only use 50% (50 amp hrs) before recharging. This is the recommended level of discharge to get the maximum life out of the battery. A 35 amp rated alternator is expected to provide 50% of its rated power (17.5 amps). That means you will need to run your engine for about 3 hours to recharge 50 amps you consumed. That’s ok if your powering for 3 hours but not good if your only using the engine for 30 minutes to get in or out of the marina.
When you start to set up your batteries and power systems it is best to think of the whole system. Generation, storage, and consumption, as you design the parts of the system.
John,
Thanks, That is a great response. And all the others as well. Also part of that is why I would want to have a battery charger when and if I am ever docked at a marina. It's an old Hunter that the wiring is a mess (where the original panels were) and i want to remove them from down at the bilge level and relocate them higher up. I will take you advice and think about the total consumption if i add devices. Thanks again!
Thanks, That is a great response. And all the others as well. Also part of that is why I would want to have a battery charger when and if I am ever docked at a marina. It's an old Hunter that the wiring is a mess (where the original panels were) and i want to remove them from down at the bilge level and relocate them higher up. I will take you advice and think about the total consumption if i add devices. Thanks again!
Found the alternator I purchased. It was from DB Electrical:
Alternator - Yanmar 1GM, 2GM, 3GM, 3HM, 4GM, 4JH2L-HTNE All 400-44041 | DBE
Alternator - Yanmar 1GM, 2GM, 3GM, 3HM, 4GM, 4JH2L-HTNE All 400-44041 | DBE