Discuss Current limited charge relay in the Electrical Forum area at ElectriciansForums.net

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Hi there, I am looking to charge an auxiliary windlass battery (130Ah lithium) that is located 35 feet away from my main bank (1030Ah lithium). My charging input will range from to 40 to 100 Amps, but I need to keep the wire size to a maximum of 6AWG. Do you know of any current limited charging relays similar to the "Mastervolt 83304002 Charge Mate Pro 40", which has a maximum output of 40A? Are there cheaper ways to achieve the same result, perhaps by combining a separate relay and dc-dc converter? Please keep in mind this is for boat and the installation needs to be worthy of the marine environment. Thanks in advance!
 

Lucien Nunes

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You don't mention the system voltage, I'll assume it's 12V. A total circuit length of 2 x 35 = 70' of #6 wire will have a resistance of about 30 milliohms. At 100A the drop along this run will be 3V, which on a 12V system is more or less unworkable without voltage boost conversion. I.e. the windlass battery would probably never see a 100A charge rate. I think the Mastervolt unit will limit the charge rate by functioning as a buck converter (that also serves as an active reverse current gate) but won't boost it.

There are products that will take an unregulated input voltage (in your case typically low due to the significant voltage drop in the cable) and buck/boost it into a chemistry-specific charging cycle for the auxiliary battery. They are essentially DC-powered battery chargers, a.k.a 'battery-to-battery' chargers, for example see this unit that does up to 120A: Sterling B-2-B

If you want to avoid the complication / cost / power loss of a boost converter, you might have to re-assess the #6 maximum cable choice or your maximum charge rate.
 
The reason why a windlass is often powered by it's own close-by battery is to avoid a large cable running from the main house bank that is often at the other end of the boat... So allowing for a charging cable that'll carry 100A is kinda defeating the purpose.

Sterling do a 'Battery Maintainer' that outputs 3A... this may form part of a better solution. If it draws say 4A... allowing for a 3% voltage drop... gives 7AWG cable ?
 
I would also have said Sterling is the most likely manufacturer of the device you want. Ring is another also Durite or Gordon equipment but these are all UK and it seems you are USA so not sure what you have over there?
 
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