Charging a battery that's different type than the house bank

[drewcathell]

From my reading and experience to date a charging system should be charging a single type of batteries, and when possible, similar age and condition. Our current setup uses an echo charger to keep our starting battery topped off between starts.

We have recently purchased an electric snooba dive system for use cleaning our boat and other recreational activities. When using it near the boat we simply connect the leads to the house bank.

However, we would like to use the snooba for diving from our dinghy which would require a separate battery. Inevitably this battery would be a different type and need to be charged from a state of fully discharged. Ideally we would like to be able to recharge it reasonably quickly. Our goal is to use the yanmar to do this but don't know how to isolate this charging task from the regular charging of the house bank.

Any suggestions. I would rather not buy a generator to accomplish this.

[mbartosch]

The common solution is to use a battery to battery (B2B) charger, such as

https://www.victronenergy.com/dc-dc-...ion-tr%20smart
or
https://sterling-power.com/collectio...ttery-chargers

Regarding the Victron Orion: make sure to pick the charger, not the converter if you actually want to charge a battery (instead of simply providing a different DC voltage)

[drewcathell]

Thanks, that gives me a place to start.

[mcon12000]

Definitely the Victron DC to DC Charger. I use one to charge my start only battery from the house bank. Two different chemistries and the house bank is a lower voltage than what the AGM Start battery requires. Not a problem with the Victron and its all accomplished and monitored via your phone.

[sailorboy1]

It all depends on what you mean by different "type" of battery. What it really comes down to is the charging voltages. As long as the new battery you are talking about doesn't need a lot lower charge voltage to prevent damage just connect it to you house system and charge it. As an example I used to have open trojan batteries that called for a voltage of 14.8, but had sealed start battery that only should have 14.4V absorption voltage. Charging at 14.8V boiled out the start battery with time. If it calls for a higher charge voltage than the house it will charge with time bit not get as well mixed, but be fine for your application.

So ...................... what are the battery types we talking about here?

[mbartosch]

Originally Posted by sailorboy1

So ...................... what are the battery types we talking about here?

Doesn't really matter if the goal is to charge an auxiliary battery quickly from a house bank which may not sit at 100 % SoC. If the batteries are simply paralleled, it will take the pack (both batteries) a long time to collectively reach 100 % if the larger battery was at a lower SoC than the smaller one.
Charge inefficiency (e. g. if the house bank is a lead acid battery) may significantly worsen that problem.

So in order to quickly charge a dinghy, snooba or whatever auxiliary battery from a house bank not sitting at 100 % SoC requires a B2B charger with the possibility to step up voltage (both the Victron and the Orion have this feature. For example the Balmar Digital Duo and - if I am not mistaken - the Xantrex Echo do not step up voltage.)

An alternative is to disconnect the house bank from the house bank when charging the auxiliary battery, so that the charging algorithm of the charger(s) can handle the aux battery directly. Only works fine if the charging profile matches both battery types.

[sailorboy1]

It most certainly matters if you plan to quickly CHARGE it and notjust connect it to a house battery that isn't charging.

But it matters little to me.

[mbartosch]

Originally Posted by sailorboy1

It most certainly matters if you plan to quickly CHARGE it and notjust connect it to a house battery that isn't charging.

Compatible battery chemistry is the precondition to proper charging of any batteries in (logical) parallel from the same charging source (otherwise only one battery of the parallel pack will be charged correctly).

Simply connecting the batteries without an active charging source will result in stray currents between the batteries (if connected at different SoC) and unwanted draw from both batteries from any loads attached.

With an active charging source paralleled batteries of the same chemistry the lowest SoC battery will draw down pack voltage, resulting in charge current mostly directed to the lower SoC battery. Upon reaching the same SoC level, both batteries will accept a fraction of the charge current roughly proportional to their capacities, from that on both batteries will reach 100 % SoC at the same time - as a pack. That means in the „parallel“ scenario there is no way to quickly charge one battery at the cost of charging the other battery slower.

Adding a charge isolator (based on diodes or a „diode simulation“ consisting of MOSFETs protects the batteries and attached consumers from each other (only allowing current draw from one branch of the isolator). In the charging situation the pack still looks like it is paralleled, resulting in identical charge time.

An „echo charger“ type device is slightly more intelligent than simple diodes or MOSFET diode simulations in terms that it switches based on voltage levels. It does not provide a battery individual charging profile to the aux battery voltage and thus does not help to solve the OP‘s problem.

This is why there are two solutions to QUICKLY charging an aux battery in addition to another battery:
1. Disconnect the larger battery from the charging source while charging the aux battery
2. Use a B2B charger for the aux battery

In case 1 it is advisable to have the same battery chemistry.
Case 2 does not care, you program the B2B charger according to the aux battery specifics.

[RaymondR]

Why is it inevitable that the battery would be of a different type?

It appears to be the easiest solution that it not be??

[Reefmagnet]

Trivial to do. You're doing it now when you charge your phone, laptop or cordless tools onboard. Use a battery charger specific for the purpose.

In this case, as already mentioned, a battery to battery (aka DC to DC) charger of the required type and capacity is the most likely solution; although if you use a generator or inverter frequently onboard then just a suitable regular mains powered charger will work also.

[drewcathell]

To add some missing info, I was thinking of going with a lithium ion battery for the snooba and yes I would want to fully charge it right away.

[drewcathell]

It is not inevitable it is just likely. My house bank are new AGM. Buying an AGM for the snooba would provide much less energy for the same weight and size.

Originally Posted by RaymondR

Why is it inevitable that the battery would be of a different type?

It appears to be the easiest solution that it not be??

[drewcathell]

I think charging my phone, laptop etc is a completely different affair. I have a 110v strip plugged into a110v outlet running off a small inverter. None of this affects the charging of the house bank.

Originally Posted by Reefmagnet

Trivial to do. You're doing it now when you charge your phone, laptop or cordless tools onboard. Use a battery charger specific for the purpose.

In this case, as already mentioned, a battery to battery (aka DC to DC) charger of the required type and capacity is the most likely solution; although if you use a generator or inverter frequently onboard then just a suitable regular mains powered charger will work also.

[drewcathell]

Thanks for all the ideas. I appreciate you all taking the time to answer. Lets try this a different way. I have a two main disconnect switches, one for the house bank and one for the starter battery. If I turn them both off and simply connect a small jumper set to the main leads coming off the alternator and run the engine into the battery is charged, is there a problem?

[Reefmagnet]

Originally Posted by drewcathell

I think charging my phone, laptop etc is a completely different affair. I have a 110v strip plugged into a110v outlet running off a small inverter. None of this affects the charging of the house bank.

Ok, perhaps my explanation was a bit too technical for you. In layman's terms, you can charge battery "b" via battery "a" via the engine charging system without having to worry that battery "a" will suck all the charge and deprive battery "b" of a charge or that battery "a" will somehow overcharge or that the chemistry is mismatched. The magic is using a dc to dc charger between battery "a" and battery "b".

If that idea doesn't appeal to you, then install a second alternator on your engine. Just don't forget to connect battery "b" to this alternator whenever running the engine to avoid the risk of blowing its diodes.